Leica Geosystems GPS Basics - Manual (Page 2)

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GPS Basics -1.0.0en
Contents
Preface ........................................................... 4
1. What is GPS and what does it do ? .......... 5
2. System Overview ....................................... 6
2.1 The Space Segment ............................................... 6
2.2 The Control Segment.............................................. 8
2.3 The User Segment ................................................. 9
3. How GPS works....................................... 10
3.1 Simple Navigation .................................................. 11
3.1.1 Satellite ranging .................................................... 11
3.1.2 Calculating the distance to the satellite ................. 13
3.1.3 Error Sources ........................................................ 14
3.1.4 Why are military receivers more accurate ? ........... 18
3.2 Differentially corrected positions (DGPS) ................19
3.2.1 The Reference Receiver ........................................ 20
3.2.2 The Rover receiver ................................................. 20
3.2.3 Further details ....................................................... 20
3.3 Differential Phase GPS and Ambiguity Resolution ...22
3.3.1 The Carrier Phase, C/A and P-codes .................... 22
3.3.2 Why use Carrier Phase? ....................................... 23
3.3.3 Double Differencing............................................... 23
3.3.4 Ambiguity and Ambiguity Resolution ...................... 24
4. Geodetic Aspects..................................... 26
4.1 Introduction ...........................................................27
4.2. The GPS coordinate system .................................28
4.3 Local coordinate systems ......................................29
4.4 Problems with height .............................................30
4.5 Transformations .....................................................31
4.6 Map Projections and Plane Coordinates .................34
4.6.1 The Transverse Mercator Projection ...................... 35
4.6.2 The Lambert Projection ......................................... 37
5. Surveying with GPS ................................ 38
5.1 GPS Measuring Techniques ..................................39
5.1.1 Static Surveys ........................................................ 40
5.1.2 Rapid Static Surveys .............................................. 42
5.1.3 Kinematic Surveys ................................................. 44
5.1.4 RTK Surveys .......................................................... 45
5.2 Pre-survey preparation ...........................................46
5.3 Tips during operation .............................................46
Glossary ....................................................... 48
Further Reading .......................................... 59
Index ............................................................. 60