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# 2008-2 - (Gm-08v LF Page 1 of 10 NTNU Geomatics Exam...

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(Gm-08v – LF) Page 1 of 10 NTNU Geomatics Exam: TBA4230 GEOMATICS Date: 11.12.2008 Time: 0900 – 1300 Solution, version 28.11.2010 Question no 1: GPS mm 1.1 Measuring methods using GPS In this question it is meant from the teacher to answer short-time-static in (a) (ev other static methods) to establish a local base point, to be able to use real time measurements in question (b) where the local base station in (a) is used. Alternatively can another base station in a commercial base station network also be used, for instance SATREF (The Norwegian Mapping Authorities) or SPIDER (Leica), then just 1 own receiver is necessary. Using such alternative methods it is not necessary to establish an own local base station (T on the figure). Therefore a suggestion of using SATREF both in (a) and in (b) will be a bit illogical. (a) - Which measuring method using GPS do you recommend to use to determine the coordinates and height of this local base point T? - Describe this method and explain why you recommend this particular method. Short-time-static method. Baseline measurements, measuring time 5-15 min, post processing. Etc Make your own assumptions and draw a figure showing the GPS measurements you are planning to do to determine the new base point. 3 known control points with good coordinates. 4 is also Ok, but with 4 it will actually be too many measurements (find an optimal measuring plane, there also time is a factor). Measuring baselines from these 3 points to point T. Eventually also measure between the known control points to be able to check out the given coordinates. (b) Describe a method for the setting-out that will be an effective way of setting-out detail points in real time with a quality (standard deviation) close to 1 cm. Describe also the instruments that are needed to perform this setting-out. Real-time-measurements (RTK, real-time-kinematic). 1 receiver in the base station T, 1 rover receiver in the other end of the baseline(s). The rover is mounted on a steady held rod. Transmittance of the corrections from the base via cell phone (or VHS, as there are short distances). 1.2 Setting-out (a) Setting out plan, coordinate calculations. Calculate the bearing from A to B. Calculate the coordinates of the corner C, assuming an angle of 100 gons in the corner B and the distance B-C is 12.000 m. From the coordinates: T

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(Gm-08v – LF) Page 2 of 10 Δ x = Δ N Δ y = Δ E Plane bearing from the calculator Correction to the correct quadrant Plane bearing Distance D kp A-B -54.300 47.281 -45.6081 200 154.3919 71.9999 The corner C, check also the figure: Bearing A-B 154.3919 Turning the bearing +200.0000 Bearing B-A 354.3919 Horizontal angle in B 100.0000 Bearing B-C 54.3919 Distance in the map projection plane 12.000 Δ N 7.8802 N = 7056893.8762 Δ E 9.0500 E = 499953.4220 (b) Why must all three terms (EUREF89, UTM, zone 32) be given to get unambiguous coordinates of a point? Datum EUREF89 to give the datum…osv UTM to show the map projection plane. UTM can be used in many datums, therefore a set of UTM coordinate values has no meaning if the used datum is not given.
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2008-2 - (Gm-08v LF Page 1 of 10 NTNU Geomatics Exam...

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