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GML SVG WFS

GML SVG WFS
GML SVG WFS

Abstract.The objective of this paper is to address two issues of current Internet Geographic Information Systems (GIS)programs –interoperability and graphic image output issues –using standard-based technologies,speci?cally,the Geography Markup Language (GML),Scalable Vector Graphics (SVG)and the OpenGIS Web Feature Service (WFS)Implemen-tation Speci?cations developed by the OpenGIS Consortium (OGC).A strategy is proposed to use GML as a coding and data transporting mechanism to achieve data interoperability,SVG to display GML data on the Web,and WFS as a data query mechanism to access and retrieve data at the feature level in real time on the Web.Two case studies are reported to implement this strategy.Our case studies show that the combination of GML,SVG,and WFS has an immense potential to achieve interoperability while not requiring considerable changes to existing legacy data.Data can be in their original formats and still be retrieved using WFS and transformed into GML in real time.SVG can produce superior quality vector maps on a Web browser.More research is needed to explore the full potential of these new standards and to test them in real-world situations.

Key words:Geographic Markup Language (GML),Scalable Vector Graph-ics (SVG),OpenGIS Web Feature Service (WFS),Internet GIS,Interoper-ability.

1Introduction

The Internet and the World Wide Web (WWW)have been widely recognized as an important means to disseminate information (Rohrer and Swing 1997;Doyle and Dodge 1998;Carver 2001;Pundt and Bishr 2002).It has The authors would like to thank Mr.Nathan Guequierre for editing the manuscript,as well as three anonymous reviewers for their valuable comments and suggestions.The authors are entirely responsible for the contents of the paper.

J Geograph Syst (2004)6:95–116

DOI:

10.1007/s10109-004-0129-0

scalable vector graphics (SVG),and Web feature service (WFS)speci?cations in the development of Internet geographic information systems (GIS)

Zhong-Ren Peng 1and Chuanrong Zhang 2

1

Director,Center for Advanced Spatial Information Research (CASIR),

Associate Professor,Department of Urban Planning,University of Wisconsin-Milwaukee,PO Box 413,Milwaukee,WI 53201-0413,USA (e-mail:zpeng@https://www.doczj.com/doc/3e11221978.html,)

2Ph.D.Candidate,Department of Geography,University of Wisconsin-Milwaukee,PO Box 413,Milwaukee,WI 53201-0413,USA (e-mail:czhang@https://www.doczj.com/doc/3e11221978.html,)

96Z.-R.Peng and C.Zhang increasingly been recognized that future developments in geographical information systems(GIS)will center on Internet GIS,accessing geospatial data and conducting geospatial analysis on the Internet(Plewe1997; Peng1999;Green and Bossomaier2001;and Peng and Tsou2003).There is active interest from researchers,practitioners,and vendors in exploiting Internet GIS and?nding ways to improve accessibility to spatial data and spatial data processing services over the Web(David et al.1998).Most,if not all,GIS vendors have created their own Internet GIS software,such as ESRI’s ArcIMS,Intergraph’s Geomedia Web Map,Autodesk’s MapGuide, MapInfo’s MapXtreme,GE SmallWorld Internet Application Server,and ER Mapper’s Image Web Server.These Internet GIS software programs provide proprietary ways to allow users to access,display and query spatial data over the Web(Plewe1997;Green1997;Stand1997;Su et al.2000; Kowal2002).

This trend has emerged to overcome several limitations of popular desktop GIS software packages.The?rst limitation of desktop GIS is that every user has to purchase a desktop GIS software package,prohibiting widespread use by the general public and small organizations who may have resource constraints in obtaining desktop GIS software and training.Moreover,the users would have to purchase the full desktop GIS package even though they may require and will use only a small percentage of the functions provided in the software.The second limitation is the inaccessibility to the Desktop GIS from locations other than the computer on which the desktop GIS software is installed.For example,GIS users cannot access the GIS data and analysis tools from remote conference sites or from the?eld.The third limitation of desktop GIS is the steep curve for learning to use the software.Due to the necessarily complicated user interface,it is di?cult for general users to quickly acquire the necessary training to conduct even a simple task such as?nding the shortest path from point A to point B.The fourth limitation of desktop GIS is proprietary technology and the lack of interoperability. Once the user makes a decision about purchasing GIS software from a particular vendor,it is very di?cult and expensive to switch to another vendor product.

Due to these limitations,access to GIS technology is limited to a few trained GIS professions,and has not reached its potential for use by other non-GIS professionals who have more limited needs from and access to GIS technology.The proprietary nature of the current GIS software products also limits the sharing of data and technology among di?erent departments even within the same organization.Since as much as80percent of public and private decision-making is based upon spatial analysis of one sort or another (Dessard2002),it is clear that desktop GIS will not su?ce to meet increasing needs for such analytical tools.Particularly,as in-car navigation systems and location-based services become popular,traditional desktop GIS is not equipped to serve the demands of the public.

Internet GIS has emerged to overcome these limitations and take advantage of the widespread use of Internet technologies.Internet GIS,or distributed GIS,is an Internet-centered GIS technology that uses the Internet as the primary means to access data,conduct spatial analysis,and provide location-based services(Peng1999;Peng and Tsou2003).Internet GIS has unique characteristics and advantages over desktop GIS.First,users

The roles of geography markup language(GML)97 have access to geospatial data and spatial analysis tools in any place with Internet access at any time.GIS usage is not limited to the o?ce as with Desktop GIS software.This greatly increases the accessibility of GIS data and tools,for GIS professionals,non-GIS professionals,and the general public.Second,the simple and friendly Web interface greatly reduces learning time and thus attracts more non-GIS professionals.The World Wide Web is nearly ubiquitous,and thus learning to use a Web-based GIS interface may be more intuitive for non-professionals.Third,users needn’t purchase full-blown GIS software.Internet GIS provides component-based geographic information https://www.doczj.com/doc/3e11221978.html,ers can potentially pay,at the time of use,only for the services(functions and data)they utilize.No signi?cant additional costs are required.With the popularity of Internet services,in-car navigation systems,and Internet-enabled mobile devices such as Personal Digital Assistants(PDAs)and cellular phones,Internet GIS and mobile GIS will play an important role in the lives of the general public and the future development of GIS technologies.

Current Internet GIS technologies rely on two major Web technologies: the Hypertext Markup Language(HTML)and the Hypertext Transfer Protocol(HTTP).However,neither HTML nor HTTP is designed to handle spatial data on the Web.HTML is a markup language that shows how each element in a text should be displayed on the Web browser,including information such as the font and the size of the text.It cannot be used to code spatial features like a point,a line,or a polygon.It is also static in that the user cannot change it once it is presented on the Web.HTTP is a communication protocol between the Web browser and the Web server.It is stateless,meaning that the Web server treats every request as a new request, so the user cannot de?ne two points on the Web browser before sending out the request to the Web server.Therefore,for Internet GIS relying on HTML and HTTP alone,it is impossible to draw a circle or a square directly on the Web browser(Plewe1997).

To overcome the limitations of the static HTML and stateless HTTP,some client-side applications have been developed,such as plug-ins,ActiveX Controls,and Java applets(Peng1999).With these client-side applications, users can work with spatial data in the form of maps,make queries,select spatial features,and draw lines and polygons just as they can do on desktop GIS.These Internet GIS applications give the general Internet-enabled public access to both GIS technologies and data.With the increased availability,previous criticism of GIS as an elitist technology(Pickles1995) may no longer be valid.We are now beginning to witness the popularizing of GIS,at least within information technology circles(Carver et al.1998).Most of these Internet GIS provide basic GIS functions and can handle client requests by allocating tasks to speci?c Map Servers.They also provide additional GIS analysis functions such as spatial query,bu?ering,address matching/geocoding,labeling,thematic displays,and distance measure-ments.Some Internet GIS applications not only handle two-dimensional spatial information,but also deliver multi-dimensional geo-referenced data (Lin et al.1999;Huang and Lin2002).These Internet GIS applications make it possible for the public to use GIS functions without purchasing desktop GIS software.

98Z.-R.Peng and C.Zhang Client-side browser add-ons also have speci?c limitations.The output received by the end-user from many current Internet GIS programs is in the form of raster image?le formats such as JPEG and GIF.Therefore,the output maps lack cartographic quality and?exibility(Cecconi and Galanda 2002).This is because most of the user requests are handled by a map server at the server end.The output image?le format is embedded in HTML pages and sent back to the Web client.In comparison with vector data,a raster format image has several disadvantages.First,raster map images tend to be of fairly low quality.The quality of the raster image is degraded as it usually has a low resolution in order to reduce the?le size.Therefore,when the user zooms for greater detail,the graphic image becomes blurred as the image’s pixel structure is magni?ed.As mentioned by Dash and Lawton(1996),a major problem with raster images is overlapping lines.A line or series of overlapping rectangles become blurred in a raster image.The second problem of raster images is that they require a large amount storage space, especially for high-resolution images.The large image data volume also slows down the data transfer speed between the Web server and the client. This is a serious problem for Internet GIS applications in terms of performance and responsiveness,as slow responses frustrate Internet users, and discourage them from using the technology.Server-side processing requires that every user request be transported to the server,thus creating high volumes of network tra?c and reducing the responsiveness of the system(Peng1999).

Another important limitation of current Internet GIS programs is that they are not interoperable.Each of these commercial Internet GIS programs has its own software design architecture and depends on speci?c database structures and formats.The mapping and geoprocessing resources distrib-uted over the Web by these Internet GIS programs cannot be shared and interoperated.Although commercial Internet GIS products are making progress in performance improvement and ease of use,they have not yet made dramatic or revolutionary changes in Web mapping(Randy2002), particularly in the area of standard-based system interoperability.A challenging task for the development of Internet GIS is to enable interoperability among heterogeneous systems and geospatial data. Proprietary client-side applications work only with their respective servers and di?erent client-side applications are unable to communicate with each other.The client-side applications cannot access data at the feature level directly from other data servers in real time(Peng2003).This is unsuitable for many applications needing real-time access to data that are located on di?erent remote servers,and often in di?erent formats.For example, emergency response services need simultaneous access to many distributed GIS databases for a particular spatial feature(such as building information at the assessor’s o?ce in Oracle database,transportation data at the department of transportation’s o?ce in the GeoMedia format,environmen-tal data at the environment agency in Shape?le format)(Peng2003).Current Internet GIS programs cannot satisfy the time requirements for these kinds of online GIS services.

To enable interoperability,approaches using distributed object technolo-gies like CORBA have been proposed(Zhu2001),but their implementation has only slowly been adopted.Open GIS Consortium(OGC)has initiated

The roles of geography markup language(GML)99 Web mapping interoperability initiatives and speci?cations(OGC2003a), including the Catalog Services Implementation Speci?cation,the Web Map Service Implementation Speci?cation,the Geography Markup Language (GML)Implementation Speci?cation,and the Web Feature Service Imple-mentation Speci?cation(OGC2003b).The OGC has organized two Web Mapping Testbeds to evaluate those speci?cations.The OGC speci?cations can potentially make the Internet an open system and extend the Internet through a new generation of standards based on Extensible Markup Language(XML)(Randy2002).The OGC Web mapping speci?cations o?er a standard way for users to search for maps and geoprocessing sources over the Web from di?erent map servers and di?erent vendors(Limp2002). But to make these OGC speci?cations work,more applications needs to be developed and more tests need to be done to verify the validity and e?ciency of these speci?cations.

This paper addresses two issues of current Internet GIS programs–interoperability and graphic image output–by using these OGC Web mapping interoperability speci?cations,particularly,the GML and the OpenGIS WFS Implementation Speci?cations(OGC2003b),in addition to the SVG,a W3C speci?cation(W3C2001).The idea is to use GML as a coding and data transporting mechanism to achieve data interoperability,to use SVG to display GML data on the Web,and to use WFS as a data query mechanism to access and retrieve data at the feature level in real time on the Web.The purpose is to test the applicability and e?ciency of integrating di?erent standard-based technologies like GML,SVG,and WFS in promoting interoperability of Internet GIS programs and improving cartographic quality of Internet GIS visualization on the Web.This is necessary because the OGC’s speci?cations were developed in a rather fragmented manner.The case studies will test whether these speci?cations can work together e?ectively and e?ciently.The following sections will introduce the concept of GML,SVG,and WFS,together with two case studies that implement these concepts.

2GML,SVG and WFS

The Geography Markup Language(GML)is‘‘an XML grammar written in XML Schema for the modeling,transport,and storage of geographic information including both the spatial and non-spatial properties of geographic features’’(OGC2003c).It is developed as an implementation speci?cation by the Open GIS Consortium to foster data interoperability and exchange between di?erent systems.GML2.1is based on the OGC Abstract Speci?cation(OGC2003d)that models the world in terms of features.A feature is an abstraction of a real world phenomenon;a geographic feature is any real-world object that is associated with a location.GML2.1models the world in terms of simple features,which are‘‘features whose geometric properties are restricted to’simple’geometries for which coordinates are de?ned in two dimensions and the delineation of a curve is subject to linear interpolation’’(OGC2001a).GML3.0can represent real-world phenomena using more complex feature types,‘‘including features with complex,non-linear,3D geometry,features with2D topology,features with temporal properties,dynamic features,coverages,and observations’’(OGC2003

100Z.-R.Peng and C.Zhang p.18).In addition,GML3.0also conforms to the ISO standards,including ISO DIS19107Geographic Information–Spatial Schema,ISO DIS19108 Geographic Information–Temporal Schema,ISO DIS19118Geographic Information–Encoding,and ISO DIS19123Geographic Information–Coverages.GML o?ers standard ways to describe these spatial features and their corresponding properties in terms of GML Schemata,including schemata to describe features,coordinate reference systems,geometry, topology,time,units of measure,and generalized values.GML applications that follow these GML Schemata standards can be interoperable.Further-more,GML provides XLink and XPointer mechanisms to make geospatial data interoperable.Through XLink and XPointer,di?erent features and feature collections,which may be located remotely,can be associated together at the feature level(Peng2003).

GML is based on XML,a data description language with strict hierarchical data structures to facilitate data search and discovery on the Web.GML is very?exible and extensible in encoding geographic features.It allows users to de?ne their own tags or elements to describe features.This is in contrast with HTML,with limited and?xed tags to describe contents. Furthermore,like XML,GML is only concerned with the representation of geographic data content.It does not specify how GML data should be presented.To represent the geospatial features in the form of maps,GML data have to be transformed through Extensible Stylesheet Language Transformations(XSLT)to style the GML geographical contents into one of the graphical formats,such as Scalable Vector Graphics(SVG),Vector Markup Language(VML)or the Extensible3D(X3D)Graphics speci?ca-tion.This process speci?es how each element in the GML data should be displayed;for example,a red dot can be used to represent a point feature,or a blue line to represent a stream.Figure1illustrates the simpli?ed process of displaying GML data on the Web browser.

Scalable Vector Graphics is an XML-based language used to describe an image,especially for display in the Web browser.It is a standard developed by the W3C(World Wide Web Consortium).As the name indicates,SVG is a vector graphic,which is di?erent from the raster image formats such as GIF,JPEG,and PNG.A vector graphic uses mathematical statements to describe the shapes and paths of an image.A raster graphic is a description

illuminate

of a bit pattern using a grid of x and y coordinates and display or Array Fig.1.The GML map making process

The roles of geography markup language(GML)101 information in monochrome or color values on a display space.The use of the word‘‘scalable’’in SVG has two meanings.First,vector graphic images can easily be made scalable,i.e.,not being limited to a single and?xed pixel size.This means SVG format can be displayed on any device of any size (whether a cell phone or a19’’computer monitor)and any resolution without changing the image clarity.This contrasts with raster image?les, which are di?cult to modify without loss of information.Second,a particular technology can grow to a larger number of?les,a large number of users,and a wide variety of applications on the Web(W3C2001).

Other characteristics of SVG include a smaller?le size and searchable text information.An SVG?le is usually smaller than a raster?le for the same map resolution and thus can be transferred across the Internet more quickly. Text information inside SVG is still text and can be searchable,while text information inside the raster?le becomes integrated into the image and is no longer recognized as text.SVG is also particularly suitable for displaying intelligent maps,because geometric objects such as points,lines,and polygons are recognized as such and are identi?able.Raster images on the other hand contain information about every pixel,and points,lines and polygons that are no longer recognizable.Therefore,the user can directly work with spatial features on an SVG but not on a raster graphic image. SVG is also based on XML and therefore conforms to other XML-based standards and technologies,such as XML Namespace,XLink,and XPoint-er.XLink and XPointer allow for linking from within SVG?les to other?les on the Web,like a GML data element,HTML pages,or other SVG?les (Boye1999).

For the development of Internet GIS,SVG has the potential to play an important role for three reasons.First,it reduces the size of the map images by allowing complex scalable cartography in a highly compressed form. Second,as an XML application,SVG provides hyperlinks to many other ?les and vector and raster graphics.It can also work directly with other XML-based technology.Third,since an SVG?le is an XML?le,it o?ers superior portability(George2001).That is,an SVG?le could be edited and displayed in any environment regardless of computer operating systems and Web browsers.The combination of these three characteristics means that SVG can play an important role in the development of Internet GIS. While GML provides a means to encode and transport geospatial features into XML,SVG provides a means to display these GML-coded geospatial features into vector maps on the Web.One issue of concern is how to conduct queries and extract features from the database to respond to user requests.The Web Feature Service(WFS)Implementation Speci?cation has been developed by the Open GIS Consortium(OGC)to serve this role. The WFS is an OpenGIS implementation speci?cation(OGC2002)that allows a client to retrieve geospatial data encoded in GML from multiple Web Feature Services.The WFS is written in XML and uses GML to represent features,but the database(or datastore in OGC’s term)could be in any format.In fact,the structure of those databases should be opaque to client applications.Any access to the database should be through the WFS interface.The data retrieval process using WFS is shown in Figure2.The client application sends a request in XML to the WFS,which connects with the datastore,processes the requests,and sends the response back to the

client.The communication between the client application and the WFS uses HTTP as the distributed computing platform.

The WFS allows the client applications to access,query,create,update,and delete data elements from the GML feature database server.The WFS provides interfaces for four basic data manipulation operations on GML features;creating,deleting,or updating a feature instance,or retrieving and querying features based on speci?ed spatial and non-spatial restraints.Client applica-tions can post request for feature level data in XML.The request includes query or data transformation operations,which can be applied to one or more features in one or more datastores,locally or remotely.The WFS server reads and parses the request and returns the result in the form of GML.

GML,SVG,and WFS are standard technologies,each of which has a unique role on the Web and Internet https://www.doczj.com/doc/3e11221978.html,bining them provides a greater potential to the development of Internet GIS.Two examples are now presented to test the feasibility of using GML,SVG,and WFS together to create a new kind of Internet GIS which is open,standard-based,interoperable,and with true vector graphics capabilities.

The ?rst case study shows the encoding of spatial features in GML and displaying the encoded GML data on the Web in the form of maps using SVG.This case study illustrates the basic concepts of GML and SVG,as well as the process of GML encoding,transformation,and SVG display.The second case study uses WFS to access and query existing data (in ESRI’s Shape?le format)at the feature level from the data server,and displays the query results in the form of SVG on the Web browser.The purpose of the second case study is to illustrate how WFS couples with GML and SVG for feature level data retrieval from di?erent data servers.

3Case study one –Encoding geospatial features in GML

and displaying the GML data as SVG on the Web browser

This case study uses GML to encode basic spatial features (points,lines,and polygons)and display them in SVG on the Web browser.The working procedure of this case study is illustrated in Fig.3.First,we encode the

spatial Fig.2.Simpli?ed WFS architecture

(Source :OGC 2001b)

102Z.-R.Peng and C.Zhang

features into GML (also called a GML feature data instance)and its corresponding GML Schema.Second,we write a Style sheet to de?ne symbols used to represent the spatial elements in the GML spatial feature data.The style sheet de?nes the symbol representing a point,line,and polygon elements.Third,we transform the GML ?le,GML Schema,and the Style sheet into the SVG format.This is done with an XSLT processor.Currently there are two popular XSLT Processors —Xalan (Apache 2003)and Saxon (Kay 2003).With the help of the Saxon XSLT processor,the GML data and the Style sheet are transformed or ‘‘styled’’into the SVG ?le for display.Finally,on the Web client side,the Adobe SVG Viewer plug-in is downloaded and installed to display the SVG ?le on the Web browser in the form of maps.

Only three real-world phenomena (or objects)are used in this case study:a building,a road,and a lake.These three spatial objects are coded in GML based on the simple feature model.That is,the building is coded in GML as a point feature,the road as a line feature and the lake as a polygon feature.These three features are viewed together as a feature collection in GML.Two types of ?les are needed to encode the spatial features in GML:a GML application ?le and one or more GML Schema ?les.The GML application ?le is also called the Feature data Instance ?le of GML,which store the feature data instance.The GML Schema ?les are created to de?ne the speci?c tags and elements used in the Feature data ?le,including geometry,topology,time,units of measure,and so on.

The following is an example of the GML codes to describe a simple point feature,the building element:

Point example <=gml :description >

Shorewood Post Office <=gml :name >

2030E :Greenway Road <=address >

377;296

<=gml :coordinates >

<=gml :Point >

<=gml :location >

<=Building >

Fig.3.Working process of GML encoding of spatial features

and SVG display

The roles of geography markup language (GML)103

104Z.-R.Peng and C.Zhang

The corresponding feature schema?le is shown as follows:

<=sequence>

<=extension>

<=complexcontent>

<=complexType>

As is shown,the above GML application instance?le and the GML feature schema do not store information about the display of the spatial feature.A Style sheet needs to be created to properly display it.

However,the Style sheet cannot be directly read by the SVG viewer(or SVG plug-in).As such the Style sheet and the GML were transformed into a SVG?le as shown below:

rule:nonzero;fill:#EBF322;stroke:#000000;stroke-miterlimit:4;}

d?}M68:262;74:51H0:5V37:255h67:762V74:51z}=>

<=g>

<=defs>

scalee2T}=>

<=svg>

Finally,the SVG?le is interpreted by the SVG plug-in on the Web browser on the client side in the form of an SVG map as shown in Fig.4.

4Case study two–Feature-level data query and retrieval using WFS

This case study uses WFS to access and retrieve existing data?les at the feature level and display them in SVG on the Web browser.The data used in this case study come from the Waukesha Transit Trip Planning Project,an

online bus trip-planning Website for the City of Waukesha,Wisconsin,which is available at https://www.doczj.com/doc/3e11221978.html,/waukesha/.The data include a bus stop ?le,a bus route ?le,and a landmark/facility ?le that are located in three di?erent servers.The ?les are originally in the ESRI Shape?le format.The working process of this case study is illustrated in Fig.5.

The ?rst step is to select and install a Web Feature Server.Currently there are several commercial WFS software programs available,such as Map-Server,developed by the University of Minnesota which has WFS support (MapServer 1996),the Ionic Web Feature Server (Ionic 2001),GeoServer (GeoServer 2002),and GeoServerLite (Rosyada 2003).GeoServerLite was chosen for this case study because it is open-source software,has a graphic client,and all other supporting software is also open-source.

GeoServerLite is a simple Web Feature Server written in the PHP scripting language,using the freely available MySQL as its backend database.GeoServerLite also has a Geoclient to be used together with GeoServerLite as a client interface on the Web browser.Both GeoServerLite and

Geoclient Fig.4.A SVG map displayed on the Web browser

The roles of geography markup language (GML)105

are developed under the GeoServer Project (GeoServer 2002)and can be downloaded from the Website at https://www.doczj.com/doc/3e11221978.html,/~amri/.

To work with GeoServerLite and Geoclient,the environment must be properly con?gured.This includes installing and con?guring an Apache HTTP Web Server (Apache 1999);installing the PHP software (PHP 2001),which is a widely used general-purpose scripting language that is especially suited for Web development;and setting up the MySQL database for GeoServerLite.These required environment setups are unique to GeoServ-erLite and Geoclient.Other WFS servers may require other setups.

The second step is to prepare the GML and SVG data.The format of the original data ?les (Bus Stop,Bus Route,and Facilities)is in Shape?le.To setup the WFS server,these Shape?le data need to be converted into the GML and SVG format.Two methods can be used.The ?rst is using ToWKT,an extension for ArcView developed by the Geoclient project.ToWKT can export the Shape?le ?les into a MySQL database in the ‘‘well known text’’format.It can also transform the Shape?le data into GML data format or SVG data format.The PHP-based GeoServerLite can connect to the MySQL database,or the GML data,or the SVG data to serve them.The second method is using FME software and Visual Basic codes to convert the Shape?le data into GML data.The GML data are then converted into SVG ?les with the help of the XSLT processor and Style sheet.The second method is more ?exible,while the ?rst is easier.To display GML ?les on the Web,an SVG or a Java Applet is needed because the GML ?le cannot specify visualization elements and legends,such as how to display a point (a red dot or a star)or a line (a red solid line or a dashed line).

The GML data with SVG format are now ready to be published to the Web by GeoServerLite.The next step is to set up the GeoServerLite server and GeoClient,and placing the GML and SVG data into the corresponding directory.This step allows the WFS server to serve data to the

clients.

Fig.5.Working process of feature-level data retrieval using WFS

106Z.-R.Peng and C.Zhang

The roles of geography markup language(GML)107 On the Web client side,the GeoClient is utilized for user interactions.But before the GeoClient can be displayed,the Adobe SVG Viewer plug-in has to be installed(Adobe2001).Alternatively,a Java applet could be written to display the GML or SVG data without GeoClient.With the GeoClient,the user can browse and analyze GML data in the form of maps on the Web browser.Figure6shows the graphic interface of GeoClient.Currently,there are only very basic map manipulation tools available in GeoClient,including zooming in,zooming out,and panning SVG data;displaying x and y coordinates as the mouse moves;displaying the legend;labeling a feature automatically according to its attribute?eld;and switching on and o?di?erent map layers.In addition,users can query the data as shown in Fig.7, which illustrates one query result.Some importation transaction operation functions de?ned in WFS implementation speci?cations have not yet been implemented in GeoServerLite.

GeoServerLite publishes GML data in two ways:static GML data with SVG formatting(static GML data serving)and dynamic GML data in real-time(dynamic data serving).The di?erence lies in that serving static GML data requires the data to be pre-converted into GML and SVG,while serving dynamic GML data does not require this data pre-conversion.The?rst procedure requires that GML data are converted into SVG format on the server side by using the XSLT processor method(method2in Fig.5)or using the toWKT method(method1in Fig.5).When the client requests the data,GeoServerLite interprets the client request and sends back the converted SVG Data(with GML attributes and coordinates)and the related documents to the client.After receiving the SVG data,the client can display

computer.

the data and perform GIS analysis with the data on his/her Array Fig.6.The graphic user interface of the GeoClient

Figure 8illustrates the static GML data transfer process between the client and the server.

The other method involves dynamically publishing the GML data on the ?y.This way,a client can access and retrieve GML data at the feature level in real-time on the Web.First,the client sends a series of requests (for example GetCapatibility,DescribeFeatureType,GetFeature,GetExtendedProject-Descriptor,GetStyledLayerDescriptor,GetExtendedLayerDescriptor)to the server.These requests are posted in the XML format.After receiving the requests,the server ?rst parses these requests,then transfers the data stored in the MySQL database,which are converted by ToWKT

from Fig.7.An example of a query result using

GeoClient

Fig.8.Static GML data transfer process between client and server

108Z.-R.Peng and C.Zhang

Shape?le into the GML format on the ?y.Next,the server produces corresponding documents with GML and sends back the query results to the client in XML.The Web client then generates the SVG on the ?y with the posted XML data.Finally,the client displays the SVG data and the user performs GIS analysis with the help of Adobe SVG Viewer.Figure 9illustrates the dynamic GML data serving process.

5Discussion

In the process of conducting the case studies integrating GML,SVG,and WFS,we have shown that these three standards are compatible and hold great promise in the future development of Internet GIS.The advantage of this standard-based approach is interoperability.No proprietary client-side applications are required;only the generic SVG plug-in is needed.Data in their original formats were retrieved using WFS and transformed into GML on the ?y.Thus,the end user can retrieve information at the feature level from di?erent data sources with di?erent data formats.Nevertheless,there are some limitations and issues to be resolved.Below is a summary of the lessons learnt so far.

5.1Standards and interoperability

GML,SVG,and WFS are standards and thus are built upon an open system.As a result,an Internet GIS program that is based on GML,SVG,and WFS is created to be compatible with other standards including XML,XSLT,Document Object Model (DOM),SMIL,HTML 4.0,and XHTML 1.0.It also has su?cient accessibility options per the W3C’s Web Accessibility Initiative (WAI)(W3C 2003).In our case studies,we found almost all

open Fig.9.Dynamic GML data transfer process between the client and the server

The roles of geography markup language (GML)109

110Z.-R.Peng and C.Zhang standards and application program interfaces(APIs)can be used to develop the Internet GIS applications.We did not have to be restricted to one language or one software program.

Because of the use of open standards,the greatest potential advantage of this standard-based Internet GIS approach is that it can access,query,and retrieve geospatial data at the feature level from di?erent data sources, locally or remotely.Theoretically,the open standards provide the foundation for the Web client to communicate with any server that conforms to the WFS Implementation Speci?cations.Moreover,both GML and SVG support XLink and XPointer,which can be used to directly link data elements at the feature level at di?erent data locations.Through XLink and XPointer, di?erent features and feature collections can be associated together, regardless of locations.GML makes it possible to link geospatial data from other departments,other cities,counties,states,or across the globe(Peng 2003).Furthermore,both GML and SVG can link geospatial data with a wide variety of non-spatial data types including text,business transactions, graphics,audio,voice,and more.

Several demonstrations are available illustrating the implementation of interoperability of this standards-based approach.GML Relay Demonstra-tion(Laser-Scan2003),which was conducted by several organizations (Laser-Scan,Intergraph,Oracle,and Snow?ake Software)in2002,and the OpenGIS Web Mapping Testbed activities(OGC1999),are two good examples of testing the interoperability of GML.These examples have demonstrated the interoperation capability of building services that combine data from di?erent sources in a seamless client user interface(Watson2001 and Lessware2000).For example,Watson(2001)allowed an Ionic client to visualize a combined map output of imagery served from an MIT server, roads from a Laser-Scan server,and hospitals from an Object/FX server.But the client side of the GeoClient has not yet implemented the mechanism to communicate with other similar WFS-compliant servers in other locations, and it cannot communicate with other WFS servers at this moment.

On the other hand,there is a potential problem in implementing GML in terms of interoperability.GML provides a standard yet extensible language to encode geospatial features in the real world,along with their associated geometries and topologies.This extensibility is a strength,but it may bring about problems in data interoperability,particularly in the use of extensible schemata.GML is extensible in that it can extend the GML applications to encode di?erent features,feature collections,geometries,and topologies. Unlike HTML,GML can create unlimited tags or elements to describe spatial objects.However,this great?exibility and extensibility could also create interoperability issues as the di?erent implementation may cause confusion about semantics,a problem demonstrated in the GML Relay(GIS Monitor2003).

5.2SVG and vector map display

Our case studies showed that SVG can deliver better and higher quality maps over the Web than raster systems.Unlike raster-based images–such as GIF and JPEG formats–SVG is a standard vector format that o?ers very high quality maps at any https://www.doczj.com/doc/3e11221978.html,ers can zoom in on any portion of SVG

data without any degradation and can view and print the high-quality maps on the Web client.There are no ‘‘staircase’’e?ects as seen when printing raster-based GIF and JPEG images.

Furthermore,because SVG conforms to the Document Object Model (DOM),it becomes possible to implement straightforward and e?cient vector graphics animation via scripting.In addition,an SVG object can be assigned to a rich set of event handlers such as on_mouse_over and on_click,which makes SVG more dynamic and interactive.

In addition,since GML separates contents from the presentation,it o?ers the user more ?exibility to display data.With the XSLT processor,users can convert GML data into di?erent graphical presentations.For example,we may style the same GML data into two di?erent SVG ?les so that the displayed maps have di?erent presentations,as shown in Figure 10.It should be noted that there are other methods besides SVG to display GML data into maps.For example,we have written a Java applet to read GML data and display GML data directly on the Web browser in another project.However,since di?erent Java applet codes may have di?erent ways to display GML data,the output may not be as interoperable as the standard SVG codes.

5.3Performance

The standard-based GML+SVG+WFS approach is a client-side applica-tion.That is,the GML and SVG data are sent to the Web https://www.doczj.com/doc/3e11221978.html,ers interact with the GML and SVG data directly on the Web client without requiring a return to the server for every operation.This is in contrast with the server-side approach,where every user operation,even a simple zoom or pan operation,has to go back to the server for processing (Peng 1999).Furthermore,this client side approach has important implications for performance.

GML data are text-based,therefore they are easier to transport over the network than images.But when GML-coded geospatial data are trans-ported,all the markup elements that describe spatial and non-spatial features,geometry,and spatial reference systems of the data are

also Fig.10.Style the same GML data into di?erent presentation graphics

The roles of geography markup language (GML)111

transported to the recipient.This is important for data interoperability, because the GML-coded data could be saved and used by any other client-side applications that can read GML data.One shortcoming of using GML as a means of transporting data is its https://www.doczj.com/doc/3e11221978.html,pared with some binary GIS data format,the size of GML and SVG data?les is large(see Table1).For example,the size of the street?le of the City of Waukesha increased from 3000Kb in Shape?le format to about9000Kb after being converted into the GML format,and to more than8000Kb after being transformed into the SVG?le.The bigger?le sizes of GML and SVG?les may hinder their use as a means of data transport over the Internet if the whole?le needs to be transported to the client at once.

The size of the GML and SVG?les is related to map resolution.By reducing the precision from millimeter to centimeter resolution,a smaller number of vertices is necessary and the GML and SVG?le size is reduced by more than50%.The size of the images,which are used by ArcIMS to transfer the spatial data,is relatively smaller(ranging from7kb to60kb for above test data)and is relatively insensitive to the data content.But the resolution of the JPEG image in the above test is only about90m(the whole map is about 540km2).For the same resolution,the JPEG image?le would be even larger than the SVG and GML?le.Therefore,there is a tradeo?between the size of the?le and the resolution precision.With GML and SVG data?les,the user can always get the full resolution map no matter how closely the user zooms in anywhere on the SVG map.But with raster image?les,the image becomes blurred when the user zooms in to the details of the map image.

Table1also shows the response time between Geoclient and ArcIMS image servers.Geoclient downloads SVG?les in full to the client while ArcIMS image server downloads the map images from the server to the client.Hence,when the?le size is small(less than200kb for the SVG?le), the initial download of the SVG?le by Geoclient is faster than by ArcIMS. But when the?le size is large(larger than200kb for the SVG?le),the performance of Geoclient deteriorates rapidly compared with ArcIMS, because ArcIMS downloads only the map images rather than the vector data.Once the SVG data are downloaded from the server,the client side Table1.File size and performance comparison

Size of shape ?le(kb)Size of GML

?le(kb)

Size of SVG

?le(kb)

Initial

download

time

by Geoclient

(second)

Operation

response

time by

Geoclient

(second)*

Initial image

download

time by

ArcIMS

(second)

Operation

time by

ArcIMS

(second)

63190.820.4 3.42 1.03 66210.840.4 3.44 1.17 431141080.880.4 3.38 1.30 60205180 1.640.4 3.56 1.18 61188171 1.950.4 3.50 1.14 135479409 2.990.4 3.47 1.16 224777660 4.910.4 3.55 1.14 5361851155910.750.4 3.56 1.85 9693208272819.520.4 3.72 1.95

*approximate

112Z.-R.Peng and C.Zhang

The roles of geography markup language(GML)113 operation by the user is very fast for Geoclient,much faster than the ArcIMS operation.This is because Geoclient works directly with SVG data on the client side while every operation in ArcIMS has to go back to the server for processing.

There are two basic means to improve the performance of SVG and GML. The?rst method is to use compression.Both GML and SVG data?les are text-based,which are much easier to compress than other formats.In fact,a compressed SVG?le format is already available.More research is needed to explore e?cient ways to compress the GML and SVG data?les on the server side and decompress them on the client side on demand.But compression and decompression may not solve the problem if the original?le size is very large.For example,if the original GML?le size is5000kb,a compression of 90%would still result in a compressed?le size of500kb.

Another way to improve the performance is to send the GML and SVG data to the client in stages or progressively.That is,send out only part of the data to the client site initially.When the client requires more data,the client then goes back to the server to retrieve other parts of the data.The size of each part would be reasonably small.This will greatly reduce the size of each downloaded dataset and improve the Web application performance.With the implementation of WFS,it is feasible for the user to extract only a small amount of data at the feature level on demand.For example,the user can only extract a few roads,or even only a road segment rather than the whole area as in the case of other commercial Internet GIS programs like ArcIMS. In summary,the standard-based GML+SVG+WFS approach to Inter-net GIS o?ers a signi?cant performance advantage on the client side.The client-side approach makes the application more responsive to user https://www.doczj.com/doc/3e11221978.html,ers can interact with the SVG viewer,conduct GIS analysis and get most responses locally rather than always having to go back to the server.Since spatial features in SVG are intelligent,they are more responsive to user requests than the traditional server-side approach.In our experience, this interaction with the GML and SVG?les is faster than the current desktop GIS programs once the initial GML and SVG?les are downloaded (seamlessly)to the local machine.But it does take more time for the initial downloading of SVG?les from the server.This performance issue can be resolved by the combination of a better compression mechanism and the progressive downloading of SVG data.

5.4Security issues in GML

GML is text-based,and can be opened using a simple text editor such as Notepad or any word processor.GML?les are therefore easy to understand, edit,maintain,and update.Like HTML?les,the user can right click the mouse to see and save the source codes of the GML and SVG?les,which can then be imported,viewed,and modi?ed in di?erent environments.Security, however,is a drawback associated with text-based formats.Because GML and SVG?les are text-based,and can be opened in any word processor,it is easy for users to accidentally alter the data.Fortunately,some XML editors have appeared on the commercial market that can prevent the accidental deletion of GML elements.Another drawback is that if some data are copyrighted,the data in GML format can be easily stolen.An encryption

114Z.-R.Peng and C.Zhang mechanism must therefore be developed to protect copyrighted or sensitive data.

6Conclusions

By using the combination of GML,SVG,and WFS,this research has addressed two major issues impacting current Internet GIS programs: interoperability and the presentation of static raster images.Our studies show that the combination of the three standard technologies has great potential to address these two issues and more.GML is an e?ective means to encode,store,and transport geospatial data.It is also an e?cient means to foster data portability and interoperability.SVG produces high-quality graphics on the Web,which is ideal for displaying spatial data and making intelligent maps.The OpenGIS Web Feature Service works well with querying and retrieving GML data from di?erent servers.

The greatest advantages of GML,SVG,and WFS are that they are open standards,and that they are based on XML.Therefore,they can work with any other XML technologies and other standard APIs.We see the possibility that they will play an important role in fostering interoperable and distributed GIS in https://www.doczj.com/doc/3e11221978.html, and Web Services framework.Conformance with XLink and XPointer,along with the use of other standards like Simple Object Access Protocol(SOAP)makes GML and SVG a great means to deliver and access component-based Internet GIS processor and geospatial data.This is a great step toward implementing truly interoperable geo-processing applications and data over the Web.

However,there are still many issues to be resolved before this can be accomplished.The three standards are all relatively new;more research and experiments are needed to test these concepts.For example,the compression of GML and SVG?les is an immediate need and probably the easiest issue to be resolved.More sophisticated client-side SVG user interfaces and data processing tools should be developed to assist users as they interact with GML data and conduct spatial analysis.

The integration of standard-based programs represents the future direction of Internet GIS,which is most likely to be Web Geoprocessing Services (WGSs)(Limp2002;Hecht2002).That is,the creation of a wide range of services that can be accessed across the Web,and Web services that can perform actions and return the outcome in a standard format to the client. GML,SVG,and WFS show great promise and could become key standard technologies to facilitate the development of Web Geoprocessing Services. By delivering geoprocessing services in the Internet’s open,standards-based environment,it will make access to and use of geodata and geoprocessing resources much easier and less expensive.In the future,WGSs combined with a wide range of scienti?c and business models could provide GIS profes-sionals and non-technical users convenient tools to perform complex analysis and build what-if scenarios on the Web based on spatial and non-spatial information.This open and standard-based Internet GIS would allow GIS technology to play an even greater role in society.Increased access to GIS analysis tools and data will certainly help both policy makers and the public to make better-informed decisions.

物质的属性与特性

物质的属性与特性 在初中物理教学中,学生往往很难分清物质的属性与特性有什么不同。其主要原因是对这两个概念本身的含义没搞清和对物理量的物理意义的理解不够深刻。 属性是所有物质共有的性质。如质量,质量是物质的量,是物体所含物质数量的多少,所有物体都有质量。物体的质量有大有小,因所含物质的多少而不同。不同物质组成的物体的质量是完全可以相同的。我们无法用质量来区分物质的不同。一桶水的质量可以是10千克,一块铁的质量也可以是10千克,我们从质量大小无法区分它们。把物质往小里分,最终都是质子、电子、中子等粒子组成的,质量实质就是它们所含的质子、电子、中子等粒子的数量不同。 特性,是一种物质特有的性质,是一种物质区别于其他物质的性质。在这种性质上每一种物质都与别的不一样。例如密度,密度反映的是同体积的不同物质其质量是不相同的,也就是不同物质的质量的疏密程度不同(特殊情况除外)。这种不同是由物质内部质子、电子、中子等粒子组成的内部结构形式不同而造成的。水的密度是1000kg/m3它的含义是每一立方米水的质量是1000kg。1000kg/m3是水所特有的。反过来说,如果有一种物质(纯净物)它的密度是1000kg/m3,我们就可以说它是水。每种物质都有自己的密度(个别除外,例如煤油和酒精,因为他们内部粒子组成的内部形式类似)。再如,2700kg/m3是铝所特有的,是铝区别于其他物质的性质。通过比较物质的密度是不是2700kg/m3,可以判断它是不是铝。 正确理解比热容。比热容也是物质的一种特性。每种物质都有自己的比热容(个别除外),用它可以鉴别物质。那么比热容反映的是物质的那一种性质呢?它反映的是同样质量的不同物质,升高(或降低)相同温度时,吸收(或放出)的热量不同。或者说不同物质容热能力不同。例如水,1kg的水,升高1℃需要吸收4200J的热量,而同质量的煤油温度升高1℃只需要2400J 的热量。反之,1kg的水,降低1℃能够放出4200J的热量,而同质量的煤油降低1℃只放出2400J,这说明水所能容热的本领大(把物体比喻为一个容器)。从这个意义说,比热容反映的是物质的容热能力,或者说是容热本领。 二十多年前的物理学中密度叫比重。现在改为密度,除纠正不是比重量的错误外,更能反映这个物理量的本义,既物体质量的疏密程度。虽然不比不知它们的不同,但是不比它们也是客观存在的,不是一个过程量,所以改掉“比”字具有深刻的意义。比热容所反映的是物质容热的本领,也是在不比较的时候同样存在,不是只有比较才存在的,似乎把它改叫热容度或热容量更能与这个物理量物理意义相符合。

权重的确定方法汇总

一、指标权重的确定 1.综述 目前关于属性权重的确定方法很多,根据计算权重时原始数据的来源不同,可以将这些方法分为三类:主观赋权法、客观赋权法、组合赋权法。 主观赋权法是根据决策者(专家)主观上对各属性的重视程度来确定属性权重的方法,其原始数据由专家根据经验主观判断而得到。常用的主观赋权法有专家调查法(Delphi法)、层次分析法(AHP )[106-108]、二项系数法、环比评分法、最小平方法等。本文选用的是利用人的经验知识的有序二元比较量化法。 主观赋权法是人们研究较早、较为成熟的方法,主观赋权法的优点是专家可以根据实际的决策问题和专家自身的知识经验合理地确定各属性权重的排序,不至于出现属性权重与属性实际重要程度相悖的情况。但决策或评价结果具有较强的主观随意性,客观性较差,同时增加了对决策分析者的负担,应用中有很大局限性。 鉴于主观赋权法的各种不足之处,人们又提出了客观赋权法,其原始数据由各属性在决策方案中的实际数据形成,其基本思想是:属性权重应当是各属性在属性集中的变异程度和对其它属性的影响程度的度量,赋权的原始信息应当直接来源于客观环境,处理信息的过程应当是深入探讨各属性间的相互联系及影响,再根据各属性的联系程度或各属性所提供的信息量大小来决定属性权重。如果某属性对所有决策方案而言均无差异(即各决策方案的该属性值相同),则该属性对方案的鉴别及排序不起作用,其权重应为0;若某属性对所有决策方案的属性值有较大差异,这样的属性对方案的鉴别及排序将起重要作用,应给予较大权重.总之,各属性权重的大小应根据该属性下各方案属性值差异的大小来确定,差异越大,则该属性的权重越大,反之则越小。 常用的客观赋权法[109-110]有:主成份分析法、熵值法[111-112]、离差及均方差法、多目标规划法等。其中熵值法用得较多,这种赋权法所使用的数据是决策矩阵,所确定的属性权重反映了属性值的离散程度。

java复习题

1、下列选项中关于Java中封装的说法错误的是()。 A、封装就是将属性私有化,提供共有的方法访问私有属性 B、属性的访问方法包括setter方法和getter方法 C、setter方法用于赋值,getter方法用于取值 D、包含属性的类都必须封装属性,否则无法通过编译 2、Java中,如果类C是类B的子类,类B是类A的子类,那么下面描述正确的是() A、C不仅继承了B中的成员,同样也继承了A中的成员 B、C只继承了B中的成员 C、C只继承了A中的成员 D、C不能继承A或B中的成员 3、分析选项中关于Java中this关键字的说法正确的是() A、this关键字是在对象内部指代自身的引用 B、this关键字可以在类中的任何位置使用 C、this关键字和类关联,而不是和特定的对象关联 D、同一个类的不同对象共用一个this 4、以下关于布局的说法,错误的是() A、BorderLayout是边框布局,它是窗体的默认布局 B、null是空布局,它是面板的默认布局 C、FlowLayout是流布局,这种布局将其中的组件按照加入的先后顺序从左向右排列,一行排满之后就转到下一行继续从左至右排列 D、GridLayout是网格布局,它以矩形网格形式对容器的组件进行布置。容器被分成大小相等的矩形,一个矩形中放置一个组件 5、以下用于创建容器对象的类是()(多选) A、Frame B、Checkbox

C、Panel D、TextField 6、以下关于抽象类和接口的说法错误的是() A、抽象类在Java语言中表示的是一种继承关系,一个类只能使用一次继承。但是一个类却可以实现多个接口。 B、在抽象类中可以没有抽象方法 C、实现抽象类和接口的类必须实现其中的所有方法,除非它也是抽象类。接口中的方法都不能被实现 D、接口中的方法都必须加上public关键字。 7、关于面向对象的说法正确的是() A、类可以让我们用程序模拟现实世界中的实体 B、有多少个实体就要创建多少个类 C、对象的行为和属性被封装在类中,外界通过调用类的方法来获得,但是要知道类的内部是如何实现 D、现实世界中的某些实体不能用类来描述 8、下列不属于面向对象编程的三个特征的是 A.封装 B.指针操作 C.多态性 D.继承 9、类所实现的接口以及修饰不可以是 A.public B.abstract C.final D.void

物质的属性(专题)

物质的属性 库尔勒市第三中学 许琼 一、选择题 1、质量为150 g 的物体可能是 ( ) A. 一个乒乓球 B. 一支铅笔 C .一个苹果 D .一只铅球 2、铁块在降温过程中,会发生变化的物理量是 ( ) A .内能 B. 质量 C .体积 D .密度 3、几种燃料的密度见下表,三辆完全相同的油罐车分别盛满这三种燃料,质量最大的是 ( ) A. 甲车 B. 乙车 C. 丙车 D. 三车重量相同 4、 如下图所示是小明在探究甲、乙、丙三种物质质量与体积关系时作出的图像,分析图像可知 ( ) A. ρρρ>>乙甲丙 B. ρρρ>>乙甲丙 C. ρρρ>>乙丙甲 D. ρρρ>>乙甲丙 第4题 第5题 5、如上图所示分别由不同物质a 、b 、c 组成的三个实心体,它们的体积和质量的关系如同所示,由图可知下列说法中不正确的是 ( ) A .a 物质的密度最小 B. b 物质的密度是3 3 1.010/kg m ? C .c 物质的密度是a 的两倍 D .b 、c 物质的密度与它们的质量、体积有关 6、下列对密度定义式v m = ρ的几种理解中,正确的是( ) A 、密度与物体的质量成正比 B 、密度与物体的质量成正比,与其体积成反比 C 、密度与物体的体积成反比 D 、密度是物体本身的一种特性,与物体的质量和体积无关 7、小王测量了五个体积、质量各不相同的铝块,将所得数据描绘成网表.图中能与实验结果吻合的是 ( )

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(1)正确性 正确性是指软件按照需求正确执行任务的能力。“正确性”的语义涵盖了“精确性”。 正确性无疑是第一重要的软件质量属性。 技术评审和测试的第一关都是检查工作成果的正确性。 (2)健壮性 健壮性是指在异常情况下,软件能够正常运行的能力。 正确性描述软件在需求范围之内的行为,而健壮性描述软件在需求范围之外的行为。 开发者往往把异常情况错当成正常情况而不作处理,结果降低了健壮性。 健壮性有两层含义:一是容错能力,二是恢复能力。 从语义上理解,恢复不及容错那么健壮。 Unix容错能力很强,可惜不好用。 Windows容错能力较差,但是恢复能力很好,而且很好用。占了90% 的操作系统市场。 (3)可靠性 可靠性是指在一定的环境下,在给定的时间内,系统不发生故障的概率。 平时软件运行得好好的,说不准哪一天就不正常了,如(千年等一回的“千年虫”问题)等。 软件可靠性分析通常采用统计方法 时隐时现的错误一般都属于可靠性问题,纠错的代价很高。例如当维护人员十万火急地赶到现场时,错误消失了;等维护人员回家后,错误又出现了。… 软件可靠性问题主要是在编程时候埋下的祸害(很难测试出来),应当提倡规范化程序设计,预防可靠性祸害。 (4)性能 性能通常是指软件的“时间-空间”效率,而不仅是指软件的运行速度。 既要马儿跑得快,又要马儿吃的少。 性能优化的关键工作是找出限制性能的“瓶颈”,不要在无关痛痒的地方瞎忙乎。 性能优化就好像从海绵里挤水一样,你不挤,水就不出来,你越挤海绵越干。 (5)易用性 易用性是指用户使用软件的容易程度 导致软件易用性差的根本原因: 理工科大学教育存在缺陷 开发人员犯了“错位”的毛病 软件的易用性要让用户来评价。 (6)清晰性 清晰意味者所有的工作成果易读、易理解,可以提高团队开发效率,降低维护代价。 开发人员只有在自己思路清晰的时候才可能写出让别人易读、易理解的程序和文档。 可理解的东西通常是简洁的。 (7)安全性

特性与属性的区别

特性与属性的区别? 简单地说:属性,即无变件的不变.比如物质的质量,惯性.其它条件再变,属性不变.特性,即有条件的不变.比如物质的密度,在常温常压下,密度是固定值,可是温度一变,密度就要变了. 特性:该物体专有的,其他物体所没有的属性;属性:属于该类物体的性质;例:人:鼻子,眼睛,嘴巴都属于人的属性;但是:你区别与其他人的属性是什么呢?找到这个就是特性了。。。这样说不知道你明白否?性质: xìnɡ zhì事物本身所具有的与他事物不同的特征化学性质: huà xué xìnɡ zhì物质在发生化学变化时表现出来的性质,如酸性、碱性、化学稳定性等。物理性质: wù l ǐ xìnɡ zhì物质不需要发生化学变化就呈现出来的性质。如颜色、状态、熔点、沸点、密度等。属性: shǔ xìnɡ事物本身所固有的性质。是物质必然的、基本的、不可分离的特性,又是事物某个方面质的表现。一定质的事物常表现出多种属性。有本质属性和非本质属性的区别。特有属性: tè yǒu shǔ xìnɡ某类事物都具有而别的事物都不具有的属性(特性、特征)。如自然界中有生命的物体,就是生物的特有属性。事物的特有属性反映到人的思想里,就形成该事物的概念。特性: tè xìnɡ 1.某一事物所特有的性质。 2.特殊的品性、品质。特性是该物质特有的性质,属性是使该物质能被判定属于什么类群的性质,性质是物质可表现出的与其它事物不同的现象。比如常温下水和乙醇和乙酸乙酯都有透明液态这个性质,但是水没有易燃这个特性,也没有有机物这个属性。物质的属性是指物质共有的性质特性是指某类物质特有的性质如质量,所有物质都有质量,是物质共有的性质如惯性,所有物质都有惯性,是物质共有的性质如导电性,不同的物质具有不同的导电性,是某类物质特有的性质,再如导热性,都是特性再如自然属性和社会属性是称为真正意义上的人的两大属性,而每个人具有不同的肤色、身高、爱好……,所以肤色、身高、爱好都是特性。 水和冰是同一种物质,只是存在的状态不同,它存在的状态决定它的密度.所以水的密度是它在某种状态下的特性.由水变成冰,发生的只是物理变化,并没有发生化学反应,物理变化是由一种状态变为另一种状态,而它的本质没有变化.它们在结构上是一样的,所以它们是同一种物质.

我国媒体公共性的属性

我国媒体公共性的属性 尽管各家之言言之有理,但笔者仍认为,因公共性定义的流动性,对新闻媒体的公共性作出永恒而固定的定义是不切实际的,我们需要的是用一些属性来对新闻媒体公共性的阐述作出框定。 1.从政府体制方面看,我国媒体的所有权由政府所有,代表人民对传媒体制进行积极的、切实可行的宏观调控 新闻媒体公共性具有民主共享性。一方面媒体的公共性并不孤立存在,它必须和一些不可撼动的基本原则结合起来探讨,包括民主、自由、平等等;另一方面就媒体体制而言,它是一种公共资源和战略性资源,具有非排他性的特点,强调最大范围的均有和最大公约数的利益满足。 新闻媒体公共性具有适当独立性。对新闻自由的呼唤由来已久,无论中外媒体,都不可能有绝对的新闻自由,均不同程度地受制于政府。但就世界范围来看,新闻自由已经取得了相当进步,媒体作为政府的牛虻,其批判和监督职能日益得到发挥和重视;其自主经营权也得到一定范围的拓展。 2.从受众服务方面看,数量巨大,是媒体服务的对象,且公民的参与意识和政治意识正在觉醒,新闻媒体公共性具有公众性 现代媒介社会已经逐渐由传者中心本位转变为受者本位,媒体服务的对象是公众,维护的是最广泛的公众利益,而公众的思考力、辨别力和批判力在逐渐增强,公民意识和要求参与社会公共事务管理的诉求也在与日俱增。 3.从媒体操作方面看,媒体的公共性是一个抽象概念,它最终落实于新闻媒体的话语表达及其实践活动中 新闻媒体公共性具有公开性。新闻是对新近发生的事实的报道,媒体的主要责任就是为人们的工作、学习、生活提供外部世界变动的新闻和信息,以有利于澄清和引导人们理解外部世界,而不是使之观念混淆。新闻信息的公开性决定了公众的知情权和监督权。 新闻媒体公共性具有实践性。媒体通过议程设置、话语实践和文本呈现等具体实践活动维护和确保公共利益,“评判某一媒体对于公共利益的贡献,其在本质上参与的公共利益事件,而不是其所获得的私有经济利益。” 新闻媒体公共性具有多样性。一方面体现为利益多元化,媒体公共性是一件华丽的外衣,其背后存在着错综复杂的权力利益关系,并受其制约,这引发出了“媒体为谁服务”,媒体、政府、商业资本以及公众之间的利益关系等问题;另一方面体现在新闻实务中,反映多方声音,提供背景材料。

Excel VBA编程 控件的共有属性

Excel VBA 编程 控件的共有属性 在VEA 中,许多ActiveX 控件都具有一些相同的属性,这些相同的属性就叫做这些控件的共有属性。下面介绍控件中常用的共有属性。 ● Name (名称)属性 该属性是所有的对象都具有的属性,是所创建对象的名称。所有的控件在创建时由VBE 系统自动提供一个默认名称。在VBE 中,Name 名称属性在属性窗口的“名称”栏中进行修改,在程序中,对象名称是作为对象的标识在程序中被引用,而不会显示在窗体上。 ● Accelerator 属性 指定控制项的对应键,也称为热键,一般用于标签、按钮或菜单的标题名称后括号内的带下划线的字母。其语法格式如下: 格式:object.Accelerator [= String] 其中,参数Object 为必选项,指定一个有效的对象。参数String 为可选项,用来指定对应键的值,值为一个有效的字母。 若要为控件指定对应键,可在【属性】窗口中Accelerator 属性中输入一个字母,或者在【代码】窗口中,以代码的方式设定Accelerator 属性的值。如果输入属性的值多于一个字符时,则字符串中第一个字符就是该属性的值。需要注意的是在控件的显示标题中也必须有与之相对应的字母。 在使用对应键时,需要按下Alt 键的同时再按下指定的字母,即可引发与之相关的事件,所引发的事件会跟据控件的不同而有所不同。 若要使用代码为控件指定对应键时,这时应该在用户窗体的Initialize 事件中。如在该事件中输入如下代码: CommandButton1.Accelerator= "C" '为控件指定热键“C ” ● A utoSiz e 属性 指定控件是否依据其内容自动调节大小。设计和运行时该属性可用。该属性的值有两个,分别为True 和False 。属性的值为True 时,控件将依其内容自动调节大小。属性的值为False (默认值)时,当控件内容超过控件区域时,只显示一部分内容,控件大小保持不变。 ● Caption 属性 该属性决定了控件上显示的内容。 ● Enabled 属性 Enabel 属性决定控件是否允许操作,属性的值分别为True 和False 。属性的值为True 时,允许用户进行操作,并对操作做出响应。属性的值为False 时,禁止用户进行操作,控件呈暗淡色。 ● Left 与Top 属性 Left 与Top 属性决定了控件在窗体中的位置。Top 表示控件到窗体项部的距离,Left 表示控件到窗体左边框的距离。对于窗体,Top 表示窗体到屏幕顶部的距离,Left 表示窗体到屏幕左边的距离。 ● TabIndex 属性 提 示 Accelerator 属性中指定的热键字符与控件中对应字符不区大小写。 注 意 每个控件,只能为其指定唯一的一个对应键。如果控件的名称为字母格式的字符串时,则指定的对应键只作用于其后的字符。如标签的的标题为Label1,指定的对应键只会对应Label1后的字符。

材质球属性对照表

材质球基本参数中英对照(blinn) Common Material Attributes(通用材质属性):各类型的材质的通用属性 Color(颜色):可设定材质的颜色,又叫漫反射颜色。 Transparency(透明):设定材质透明属性,Maya 的Transparency 是通过颜色来设定的。 Ambient Color(环境色):设定材质的环境颜色。使用Ambient Color,可以模拟光能传递效果,而不使用光能传递的渲染器。 Incandescence(自发光):设定材质的自发光属性,Maya 的Incandescence 是通过颜色来设定的。 Bump Mapping(凹凸贴图):指定凹凸纹理贴图。 Diffuse(漫反射度):设定材质的漫反射度,对于玻璃、金属等物体,我们一般使用较低的Diffuse,而对于木材、水泥等物体,我们一般使用较高的Diffuse。 Translucence(半透明度):设定材质的半透明度,常用于玻璃、水晶等透明材质的表现。 Translucence Depth(半透明深度):设定材质的半透明深度。 Translucence Focus(半透明焦聚):设定材质的半透明焦聚程度。 Special Effects(特效):Maya 的Special Effects(特效)是控制物体的辉光效果的Hide Source(隐藏源):勾选该项,可平均发射辉光,看不到辉光的源。 Glow Intensity(辉光强度):设定辉光的强度。 Specular Shading(高光着色):这里以Blinn 材质类型为例,来介绍高光的参数,其他类型的材质的高光控制大同小异。 Eccentricity(离心率):设定高光区域的大小。 Specular Roll Off(高光扩散):设定高光区域的扩散和凝聚。 Specular Color(高光色):设定高光区域的颜色。 Reflectivity(反射率):设定反射率,该参数越大,材质反射能力越强。 Reflectivity Color(反射色):设定反射颜色,Reflectivity Color 对于金属、玻璃等材质的表现至关重要,我们常常在Reflectivity Color 属性上指定纹理贴图来模拟反射环境。 Matte Opacity(遮罩不透明度) Matte Opacity Mode(遮罩不透明模式):有Black Hole(黑洞)、Solid Matte(实体遮罩)以及OpacityGain(不透明放缩)三个选项,其中Black Hole(黑洞)不渲染该材质的物体,并在Alpha 通道中留该物体的洞,且与Matte Opacity 参数值无关。在下面笔者给出它们的示意图。 Matte Opacity(遮罩不透明度):设定遮罩的不透明度。该参数值为1 时,完全不透明,Al pha 通道中不会出现物体的Matte;该参数值为0 时,完全透明,Alpha通道中出现物体的Matte。Raytrace Options(光线追踪选项):使用光线追踪可以根据物理规律计算光线的反射、折射,得到较真实的效果。 Refractions(折射):勾选该项,可打开该材质的折射。但最后我们还要在RenderGlobals 中打开Raytracing(光线追踪),才可以真正得到折射效果。 Refraction Index(折射率):设定材质的折射率 Refraction Limit(折射限制):设定折射的次数。 Light Absorbance(光线吸收率):设定光线穿过透明材质后被吸收的量。光线每经过一次折射,都会有一定衰减,衰减的部分可以看成被吸收的部分。 Surface Thickness(表面厚度):模拟表面的厚度,可影响折射效果。 Shadow Attenuati on(阴影衰减):表现玻璃等透明物体时,可以设定阴影的衰减,以表现阴影的明暗、焦散等现象。 Chromatic Aberration(色差):打开该项,在光线追踪时,在透明物体间可以通过折射得到丰富的彩色效果。 ————————————— Reflection Limit(反射限制):设定反射的次数。 Reflection Specularity(镜面反射强度):设定镜面反射的强度,该参数越大,反射效果越强烈。

材质球属性介绍

Common Material Attributes 通用材质属性 Color 颜色(设定材质颜色,又叫漫反射颜色) Transparency 透明(设定材质的透明属性,黑为不透明,白为透明) Ambient Color 环境色(设定材质的环境颜色,可以模拟光能传递效果) Incandescence 自发光 Bump Mapping 凹凸贴图 Diffuse 漫反射度(一般玻璃、金属的较低,而木材、水泥较高) Translucence 半透明度 Translucence Depth 半透明深 Translucence Focus 半透明焦距 Speular Shading 高光着色 Eccentricity 离心率(设定高光区域的大小) Specular Roll Off 高光扩散(设定高光区域的扩散和凝聚) Specula Color 高光色(设定高光区域的颜色) Reflectivity 反射率(该参数越大,材质反射能力越强) Reflected Color 反射颜色(可以指定纹理贴图来模拟反射环境) Special Effects 特效,控制物体的辉光效果 Hide Source 隐藏源(勾选该项,可平均发射辉光,看不到辉光的源) Glow Intensity 辉光强度 Matte Opacity 遮罩不透明 Matte Opacity Mode 遮罩不透明模式 Black Hole 黑洞(Black Hole不渲染该物体,并在Alpha通道中流出该物体的) Solid Matte 实体遮罩 Opacity Gain 不透明缩放 Matte Opacity 遮罩不透明度(该参数为1时,完全不透明,Alpha通道总不会出现 物体的Matte,该参数为0时,完全不透明,Alpha 通道中出现物体) Raytrace Options 光线追中,可根据物理规律计算光线反射、折射,得到较真实的效果Refractions 折射(勾选该项,打开折射,但还要在Render Globals中打开Raytracing 光线追踪,才真正达到折射效果) Refractive Index 折射率 折射率—大气:1.00 烟雾:1.02 冰:1.30 水:1.33 玻璃:1.44 石英:1.55 红宝石:1.77 水晶:2.00 Refraction Limit 折射限制(设定折射的次数) Light Absorbance 光线吸收率(设定光线穿过透明材质后被吸收的量,光线每经过 一次这是都会衰减,衰减的部分可以看做被吸收的 部分) Surface Thickness 表面厚度(模拟表面的厚度,可影响折射效果)

材质属性

RAYMTL为VRAY标准材质 漫射:相当于物体本身的颜色 反射:黑与白的过度,受颜色的影响很小,越黑反射越小,反之越白反射越大。 在黑天,所有的物体都是黑色的,因为没有光,白天因为有光,太阳光由三种颜色,光 照到物体上,其他的颜色被物体所吸收,反射出物体本身的颜色,所以我们就看到物体。 折射:透明、半透明、折射:当光线可以穿透物体时,这个物体肯定时透明的。纸张、塑料、蜡烛等物体在光的照射下背光部分会出现“透光”现象即为半透明。由于透明物体的密度不同,光线射入后会发生偏转现象,这就是折射,比如水中的筷子。而不同密度的物体折射率不同。 墙面漆漫射245 发光贴图于灯光缓存反射20-25 高光0.25 选项去掉第一个提高渲染速度VR 是双面显示材质的,可以去掉,细分12-16 顶面,和墙面一样,细分12-16 白色油漆,漫射255 ,反射25-30 ,高光0.85-0.88,光泽0.9,细分16 皮革材质测试渲染:创建一个地面,创建,VR,平面, HDRI 光照贴图,倍增器1.0 球形环境贴图CTRL+C快速建摄像机。 漫射一个相对白的颜色,可以偏米黄色,反射20-45之间,皮革的发亮程度,(如果是红色,需要复制一个到衰减里的第一个。) 在反射里给一个衰减效果,非聂耳反射。高光0.6。 光泽度0.7。0.6-0.75之间 地毯材质:标准材质漫射给一个纹理的颜色,置换中给一个地毯的材质,25,给一个毛发的材质,就是带毛毛的。其他的不用调节,VR毛发在8-15之间,平铺参数默认1.0改为2.0。 液晶电视:TV-1 塑料漫射,一个浅蓝的颜色,反射40--70之间,0.9高光,光泽度0.8,非聂耳打开,不然材质会像金属一样。 TV-2 黑塑料,相当于音响,漫射黑色,反射20,高光0.6 光泽度0.7 TV-3 标志漫射白色,反射20 高光0.8 光泽度0.9 TV-4 屏幕漫射黑色,反射160-220 非聂耳高光0.9 光泽度0.98 给它一个VR灯光贴图,玻璃瓷器和金属材质:玻璃漫射前蓝色,反射180-220(反射越高,效果越好)非聂耳(如果不勾选就会像钢制的效果)高光0.88 光泽度1 细分16 折射240-250。折射率表1.7(默认也行)影响阴影打开(一般有透明的材质都需要打开这个)烟雾颜色(烟雾的颜色在这里就是玻璃的颜色,颜色越重,玻璃的颜色就越重。) 瓷器,漫射前白色(可以自己调节。),反射180-220(反射越高,效果越好)非聂耳(如果不勾选就会像钢制的效果)高光0.88 光泽度0.9 细分8 金属,漫射蓝黑色,反射180-220 高光1 光泽度0.75 镜子和金属很相近,没有光泽度。漫射为纯黑。 清漆木材材质:(光亮材质)漫射给一个贴图,颜色可以默认。反射20--30 高光0.85 光泽度1 细分8 (磨砂材质)漫射给一个贴图,颜色可以默认。反射45 高光0.85 光泽度0.9 细分8 木地板材质: 光亮木地板材质和磨砂木材挺像的,漫射给一个贴图,颜色可以默认。反射20--30 高光0.85 光泽度1 细分8 磨砂木地板材质和磨砂木材挺像的,漫射给一个贴图,颜色可以默认。反射45 高光0.85 光泽度0.85细分8 较清晰的木地板材质的方法,用一个插件,点击漫射贴图,位图形式,给一个颜色校正插件,COLORCORRECT 亮度-0 5 对比度110左右, 凸凹位图,黑白的图片,将漫射复制,点击进去,将其改为单色,8--12 之间,()太大影响速

基于属性权重向量组的多属性决策方法

第40卷第5期 2017年5月 合肥工业大学学报 (自然科学版) JOURNAL OF HEFEI UNIVERSITY OF T ECHNOLOGY Vol .40No .5 May 2017  收稿日期:2016‐03‐08;修回日期:2016‐07‐30基金项目:中央高校基本科研业务费专项资金资助项目(J 2014HGXJ 0080;JZ 2016HGBZ 0809) 作者简介:段传庆(1978-),男,安徽淮南人,博士,合肥工业大学讲师. DOI :10.3969/j .issn .1003‐5060.2017.05.026 基于属性权重向量组的多属性决策方法 段传庆1,2, 涂振坤2 (1.合肥工业大学管理学院,安徽合肥 230009;2.合肥工业大学数学学院,安徽合肥 230009) 摘 要:文章基于属性权重完全未知的直觉模糊多属性决策问题,提出了一种属性权重向量组的决策方法。该方法认为决策对象应具有独立的属性权重,结合熵与离差最大化,确定所有选项的属性权重,构成一个权重向量组,并通过理想解与选项之间的关联系数进行排序。最后,文章通过算例说明了该方法的可行性。关键词:直觉模糊数;熵;向量组;关联系数 中图分类号:C 934 文献标识码:A 文章编号:1003‐5060(2017)05‐0708‐04 Approach to multi ‐attribute decision making based on vector group of attribute weights DU AN Chuanqing 1,2 , T U Zhenkun 2 (1.School of M anagement ,Hefei U niversity of T echnology ,Hefei 230009,China ;2.School of M athematics ,Hefei U niversity of T ech ‐nology ,Hefei 230009,China ) Abstract :T his paper proposes an approach to multi ‐attribute decision making based on vector group of attribute weights with unknow n attribute weights information w here individual assessments are pro ‐vided as intuitionistic fuzzy numbers .In this approach ,it is considered that the decision objects have independent attribute weights .To gain the attribute weights ,a new method is proposed based on the entropy and maximizing deviations .T hen the vector group of attribute weights is gotten .And a meth ‐od for ranking the alternatives by correlation coefficient is proposed .Finally ,an example is given to illustrate the effectiveness of the method .Key words :intuitionistic fuzzy number ;entropy ;vector group ;correlation coefficient 0 引 言 在传统模糊集[1] 基础上,文献[2‐3]提出了直 觉模糊集的概念。由于直觉模糊集同时考虑到隶属度、非隶属和犹豫度3个方面的信息,因此它比传统模糊集在处理模糊性和不确定性问题方面具有更大的灵活性。 在模糊集理论的决策问题中,属性权重往往起着至关重要的作用。但在实际问题中,属性权重常常由于决策者缺少数据或对该数据不了解而具有不确定性。如何确定属性的权重是决策理论的热门话题。熵权法是一种客观赋权法,国内外学者已做过大量的相关模糊熵研究[4‐9] 。文献 [10]用模糊熵来确定属性的权重,但模糊熵往往只注重信息本身的重要性,而忽略了信息间存在的联系。文献[11]用离差法确定属性的权重,但离差法只注重信息间的关系而忽略了信息本身的重要性。再者从实际经验看,由于决策对象具有一定的独立性,即使是不同决策对象的同种属性,其在事物中起到的作用也不同,因而赋予的权重也不应相同。文献[10‐15]在讨论过程中对不同决策对象的同种属性取同一权重,这具有一定的不合理性。文献[11]对5种ERP 软件进行评估,选取了软件技术水平、功能满足程度、系统性能、 万方数据

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