THE DEVELOPMENT OF A GPS SURVEYING PROBE

Transcription

1 THE DEVELOPMENT OF A GPS SURVEYING PROBE ROCK SANTERRE, STÉPHANIE BOURGON AND MICHEL BOULIANNE CENTRE DE RECHERCHE EN GÉOMATIQUE UNIVERSITÉ LAVAL QUÉBEC, CANADA IAG 001 SCIENTIFIC ASSEMBLY BUDAPEST, HUNGARY -7 SEPTEMBER 001

2 ABSTRACT This poster presents the development of a new concept and the realisation of a new GPS tool to enable the survey of obstructed points or points impossible to reach with conventional GPS methods. The conventional GPS methods use an antenna mounted on a tripod or on a vertical pole. The GPS surveying probe, developed at the Centre for Research in Geomatics at Laval University, consists of two GPS antennas located along a telescopic pole. The probe can be held in an inclined position in situations where it is not possible to set-up a GPS antenna vertically above the point to be surveyed; and to move away antennas from obstructions in order to facilitate the tracking of GPS signals. The three-dimensional coordinates of the two GPS antennas on the surveying probe are determined with respect to a GPS reference station. By knowing the distance between the two antennas on the probe and the distance between one of these antennas and the probe tip, the position of a point reached by the probe tip can be determined. Field tests have shown that the coordinates of the probe tip can be determined with an accuracy of a few centimetres. These results were obtained using 1-channel, C/A-code receivers with L1 ambiguity fixed solutions and a reference station located less than one kilometre from the probe. The geometry of the GPS positioning is advantageously modified by using constraints into the solutions. The constraints are: the known distance between the two antennas on the probe; and the vertical angle of the probe measured by a digital clinometer. With this two constraints, the number of GPS satellites received by one of the antenna on the probe can be reduced to only two satellites. The GPS surveying probe can be used to determine the three-dimensional coordinates of various points in situations where GPS conventional methods would not have been practical. This new concept extends the use of GPS in the fields of surveying and engineering geodesy.

3 OBJECTIVE 1 To develop a GPS surveying probe enabling the survey of obstructed points or points impossible to reach with conventional GPS methods (an antenna mounted on a tripod or on a vertical pole) The new GPS surveying probe can be held in an inclined position to measure vertically inaccessible points and to move away antennas from obstructions in order to facilitate the tracking of GPS signals

4 GPS SURVEYING PROBE Technical description : Two single frequency GPS receivers Two GPS antennas Digital clinometer Telescopic pole Length :.4 m m Weight : 10 kg Material : nylatron GS United States patent : US Canadian patent pending : CA Third place winner to the GPS World Applications Contest 000

5 GPS PHASE AMBIGUITY RESOLUTION (L1) 3 Initial ambiguities antenna 1 * Combinations (± cycles) Test #1 : coordinates Test # : residuals Initial ambiguities antenna * Combinations (± cycles) Test #1 : coordinates Test # : residuals Combinations of the two probe antennas Test #3 : distance between the two probe antennas Test #4 : vertical angle of the probe Test #5 : ratio of a posteriori variance factor * with respect to a GPS reference station Only one combination? Ambiguities fixed

6 CONSTRAINED ADJUSTMENT 4 h 1 D 1 Z 1) Vertical distance between the two probe antennas : h = 1 D1 cos Z Vertical angle of the probe measured by a digital clinometer ( σ = ± 0. ) : Z 0 0 cosϕ cosλ (xˆ xˆ 1) cosϕ sinλ (ŷ ŷ1) + 0 sinϕ (ẑ ẑ ) h = 0 ϕ 0,λ : approximate latitude and longitude of one antenna ) Known distance between the two probe antennas ( D 1 = m ± 0.001m) : ( xˆ xˆ 1) + (ŷ ŷ1) + (ẑ ẑ1) D1 = 0

7 COORDINATES OF THE PROBE TIP 5 Antenna xˆ, ŷ, ẑ D t D 1 Antenna 1 xˆ 1, ŷ1, ẑ1 xˆ Probe tip D D t x t= 1 1 ( xˆ xˆ ) Dt yt = ŷ ( ŷ ŷ1) D 1 Dt z t= ẑ ( ẑ ẑ1) D 1

8 DESCRIPTION OF FIELD TESTS 6 Session Point Az ( ) Z ( ) D t (m) Receivers Geodetic points Typical points NovAtel NovAtel Marconi 4 PILC Marconi 5 PILC Marconi 6 ABRI NovAtel 7 ABRS NovAtel 8 BATI Marconi 9 BATS Marconi 10 LAMP Marconi The GPS reference station was located less than 1 km from the probe

9 RESULTS ON GEODETIC POINTS 7 Sess. Epochs DOP Mean (cm) RMS (cm) Point Satellites N E V Constraints N E V N E V None D1 & Z None D1 & Z None D1 & Z None PILC 7 D1 & Z None PILC 6 D1 & Z

10 RESULTS ON A GEODETIC POINT (7607, session 3) 8 a) Without constraints b) With constraints on the distance between the two probe antennas and the vertical angle of the probe

11 RESULTS ON TYPICAL POINTS 9 Sess. Epochs DOP Mean (cm) RMS (cm) Point Satellites N E V Constraints N E V N E V None ABRI 5 D1 & Z None ABRS 6 D1 & Z None BATI 6 D1 & Z None BATS 5 D1 & Z None LAMP 5 D1 & Z

12 RESULTS ON A TYPICAL POINT (BATI, session 8) 10 a) Without constraints b) With constraints on the distance between the two probe antennas and the vertical angle of the probe

13 CONCLUSIONS 11 The GPS surveying probe can be used to determine the three-dimensional coordinates of various points in situations where GPS conventional methods would not have been practical Example of applications : Corners of buildings Electricity and telephone poles Buried gas and water pipes Submerged points (shallow water) Benchmarks embedded in walls Field tests have shown that the three-dimensional coordinates of the probe tip can be determine with an accuracy of a few centimetres Using constraints into the solutions advantageously modify the geometry of the GPS positioning

14 FURTHER RESEARCH AND INFORMATION 1 Further research : The development of an alternative probe that replaces the GPS antennas by two corner cubes used in association with a total station For more information : under research/patents A full paper will be published soon in Geomatica (Journal of the Canadian Institute of Geomatics) ACKNOWLEDGEMENTS Fonds pour la Formation de Chercheurs et l'aide à la Recherche du Québec Natural Sciences and Engineering Research Council of Canada Centre for Research in Geomatics