Sample questions(1)

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B. When immediate correct positioning is not necessary, we can get differential corrections in a …. Post procesion message…..contains the most important information the GPS receiver needs to know about, amongst others, the quality of the satellite clocks, orbital information and where to find other satellites. D. Each satellite carries onboard its own very stable & accurate ……atomic clock..
Question 3 – Spatial Reference Frames (4%) Analyse carefully the following diagram about spatial reference frames and datum transformations specifically. Insert the following terms in the appropriate text boxes. Do mind you have 9 boxes and 8 terms, so one box should remain empty. • • • • • • • • Map projection Inverse mapping equations 3D conformal transformation Coordinate conversion Datum transformation via geographic coordinates 7 parameter Helmert transformation 2D Cartesian transformation Polynomial
Student code number
or, alternatively, your name:
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GFM Master of Science Degree Course EXAMINATION Module 6: Base Data Acquisition Date: 15 February 2013 from 09.00 till 12.00 hours
x' 2 x 3 y z ' y x z z ' 5 y 2 z
a) Write the transformation matrix;
2 1 0
3 0 5
1 1 2
1 b) Apply the transformation matrix to transform the vector v 2 and write the result. 3 2 1 0 3 0 5 1 1 1 1 2 2 2 3 4
Question 2 – Spatial Reference Frames (1%) You measure a bench mark of the Dutch geodetic network with differential GPS. The bench mark in the geodetic network is defined as (250000, 489000, 34.55m). However, your GPS system shows (5.235°, 52.235°, 84.45m). Explain briefly the cause of the big difference in the third coordinate value using your knowledge about spatial reference frames. The bench mark has leveled height with respect to a selected mean sea level (Geoidal height). Whereas the GPS measures with respect to ellipsoidal height. That causes the big difference; Geoidal height and ellipsoidal height can differ 100 m locally. Just mentioning different datums used is not sufficient.
Question 5 (3%) Explain why corrections between GPS receivers becomes weaker as the rover gets farther from the base, while measuring in differential GPS mode? (3%)
2. 3. 4.
5.
6.
Linear algebra and spatial referencing (10%) Question 1: Transformations (5%) The following transformation is given in the form of a system of equations:
Polynomial
0.5 % per correct answer.
GPS (10%) Question 4 (3%) Which of the following errors is not eliminated by using relative or differential GPS? Tick the correct answer The ionospheric effect The tropospheric effect Multipath Satellite clock error Clearly explain your answer. Multipath, as this only occurs in one of the receivers. It can therefore not be corrected by using the gps positions at the base stations. The other errors are systematic in the sense that they influence both gps observations to the rover receiver and the base station, and therefore can be corrected by DGPS.
3D Conformal trans.
7 parameter Helmert Coordinate conversion Datum trans. via geographic coordinates
Inverse mapping equations
Map projection
2D Cartesian trans.
The influence of the atmosphere becomes different for both gps receivers if the distance between rover and base gets larger. That is why a correction, calculated at the base, is not that precise anymore for the rover. (Also different satellites may be tracked, one point is given to that answer).
Question 6 (4%) Fill in the words to complete the following four statements. Choose from the following terms (no need to use every term): phase measurements, code measurements, atomic clock, real time kinematic, post processing, multipath, almanac, navigation message, carrier wave. A. By applying differential corrections to ……phase measurements……, positions can be obtained to an accuracy of cm level.
1.
Subjects covered by the attached examination paper: Linear algebra and spatial reference frames (10%) GPS (10%) Digital VHR sensor systems and topographic mapping (20%) Sensor orientation (25%) DTM (20%) Orthophoto production (15%) The time available for this examination is three hours. The weight of each question is shown on the paper. The examination is CLOSED BOOK; you are not allowed to use your lecture material or personal notes. Once the examination has begun you may not communicate with other students, but you may ask supervisors to clarify the questions. The examination paper is to be handed in to the supervisor at the end of the examination and may not be removed from the classroom by the students under any circumstance.