GPS area measurements

Transcription

1 GeoCAP Annual Conference, Taormina, November / 27 GPS area measurements Krasimira Galabova, Aleksandra Sima GeoCAP, JRC Ispra

2 GeoCAP Annual Conference, Taormina, November / 27 Outlines GPS devices certified up to now by Navcert or validated by MS with JRC support GPS measurements of small features DGPS versus Standalone Results on EGNOS implementation in 2009

3 GeoCAP Annual Conference, Taormina, November / 27 GPS devices certified by Navcert up to now Device Measurement method Category (buffer) Farmphone continuous B (0,6m) LACOS pocket Area continuous B (0,7m) StarFire itc continuous A (0,3m) TOPCON GMS-2 vertex B (0,8m) Trimble Pathfinder ProXRT vertex B (0.5m) Trimble Pathfinder ProXRT with Trimble VRS Now Trimble Pathfinder ProXT with EGNOS vertex vertex A (0,1m) A (0,2m) Trimble GeoExplorerXT with Trimble VRS Now vertex A (0,2m)

4 GeoCAP Annual Conference, Taormina, November / 27 GPS devices validated by MS with JRC support MS Device Method Buffer (m) GR Garmin 60 continuous 1,25 (except if trees) BG Magellan MobileMapper CX vertex/continuous 0,75 + voice application CZ Topcon Legacy H - DGPS continuous 0,75 DE Topcon GMS 2 + Beacon vertex 0.75 SI UK JRC (PL) Trimble GeoExplorerXT with EGNOS Trimble Pro XRS (Beacon and OmniStar corrections) Trimble GeoExplorerXT and Trimble GeoExplorerXH vertex/continuous 0,75 vertex <0,50 continuous 0,75

5 GeoCAP Annual Conference, Taormina, November / 27 Summary on experimental design of the various tests made by Navcert and MS From 5 to 7 parcels, mode = 6 From 1 to 6 devices (usually 3) From 2 to 6 operators From 3 to 12 sets (we recommend 8 or 12 sets) From 2 to 5 repetitions (we recommend 4 or 6 to test CW/ACW effect)

6 GeoCAP Annual Conference, Taormina, November / 27 Summary of GPS measurements of small features study Common idea: it is not appropriate to measure small areas with GPS Reason: Because the tolerance is too large... When compared to the parcel area (tolerance>>5%) Objective determine the buffer width of a GPS receiver when measuring small objects and verify if the buffer varies with the size of the measured object Objects - very small objects, with sizes between 32 m 2 and 655 m 2 and perimeters between 23 m and 115 m Device - F@rmhone (ASUS P526 with external antenna mounted on a cap), certified by Navcert (Cat B, 0.60m)

7 GeoCAP Annual Conference, Taormina, November / 27 Objects measured - reference 10 fields Some obstacles

8 GeoCAP Annual Conference, Taormina, November / 27 Design of the test The test was performed on 10 specially designed fields The test site was designed partly under the tree canopy The data is logged with a time interval of 1 second For each field: 5 sets of measurements with 4 repetitions each (2 CW + 2 ACW) taken over 3 days, in total 200 measurements 16 measurements detected as outliers and excluded from further processing of the data

9 GeoCAP Annual Conference, Taormina, November / 27 Samples of the data collected

10 GeoCAP Annual Conference, Taormina, November / 27 An example of the variability of measurements Area may be OK, but measurement might not be OK for mapping purpose

11 GeoCAP Annual Conference, Taormina, November / 27 Results (1/3) R limit (buffer on perimeter) as a function of area R ranges from 0.3 to 0.7m (Navcert m) No dependence on area measured Average R limit = 0.49m

12 GeoCAP Annual Conference, Taormina, November / 27 Results (2/3) Tolerance ((buffer*perim)/ref area)) in % as a function of the reference area Tolerance in % of the reference area 35% 30% 25% 20% 15% 10% 5% 0% Tolerance can be up to 30% of parcel area (0.02 ha) but in absolute value is 0,007ha Average tol = 18% reference area [sqm]

13 GeoCAP Annual Conference, Taormina, November / 27 Results (3/3) Tolerance in % vs area Simulation: Rectangular parcels of 50m 2 to 5000m 2, L/l from 1 (square) to 10 Tolerance in % of the reference area 130% 120% 110% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Buffer width 1,25m Reference area (sqm) Small objects have large tolerance in relation to area (>5% even for 0.5 ha parcels) but in absolute terms, the tolerance is small: for parcel size ha -> tolerance varies from 0,005-0,028 ha (for buffer of 1.25m)

14 GeoCAP Annual Conference, Taormina, November / 27 Summary of conclusions The reproducibility limit R does not depend on the area measured: the same R limit was found on small and larger parcels In relative terms, the tolerance (buffer*perimeter) is large for very small objects (>10% for parcel <0,02ha) but small in absolute value 0,002-0,007ha); Pay attention to spikes : higher occurrence of outliers were observed on small parcels.

15 GeoCAP Annual Conference, Taormina, November / 27 DGPS vs Standalone Purpose What is the improvement of differential correction of GPS signal on area measurement? Correction provider: GPS Lombardy providers of real time differential corrections and post-processing data (

16 GeoCAP Annual Conference, Taormina, November / 27 Design of experiment Trimble Geo XH receiver tested Two parcels inside JRC, Ispra site Four modes tested and compared: 1. DGPS - differential code corrections (meter accuracy) 2. VRS4km - carrier-phase correction via Virtual stations (decimetre accuracy) 3. Post processing of standalone data using our own base station (meter accuracy) 4. Standalone/uncorrected GPS Continuous measurement mode

17 GeoCAP Annual Conference, Taormina, November / 27 Test field Area = 0,53ha, P = 290m Area = 0,16ha, P = 218m

18 GeoCAP Annual Conference, Taormina, November / 27 Test performance Two operators, four sets (4 days) with four repetitions in each set (2 cw and 2 acw), 3 modes (stand alone, DGPS, VRS4km) In total, 96 measurements were carried out per parcel Parcel 1 Parcel 2

19 GeoCAP Annual Conference, Taormina, November / 27 Data collected in each mode DGPS Virtual Station Standalone After Post processing

20 GeoCAP Annual Conference, Taormina, November / 27 Statistical tests Outlier detection - by means of Cochran s and Grubb s test Two out of 192 observations were not included in the calculation of the final results Analysis of variance: 1. Factor: operator and border (field) NOT significant 2. Factor: measurement direction significant (for 1 operator) The direction effect was omitted in the analysis (to keep a sufficient number of measurements)

21 GeoCAP Annual Conference, Taormina, November / 27 Results There was no significant bias in the measurements The overall reproducibility limit of the area measurements, expressed as a buffer on perimeter: 1. Virtual station is 0.35 m (with only one operator with no direction effect = 0.18m - test to be continued with vertex method) 2. DGPS is 0.40 m (0,30m with one operator) 3. After post-processing is 0.48 m 4. Standalone GPS is 0.53m (0,43m one operator) Differential correction improves the accuracy of area measurement by 25% (( )/0.53) to 34% (with VRS) Do other tests confirm these results?

22 GeoCAP Annual Conference, Taormina, November / 27 Comparison with other tests (buffer) Stand-alone DGPS JRC 0.5m (GeoXH this test) 0,7m (GeoXH, PL 2009) 0,5m (GeoXT, PL 2009) 0.4m (GeoXH this test) 0.3m (GeoXT+EGNOS in 2004, only 1 parcel) Navcert 0.5m (ProXRT) 0.2m (ProXT+EGNOS) VRS 0.35m (GeoXH this test) (0.18m one operator continuous mode) 0,2m (GeoXT) 0.1m (ProXRT) Vertex mode

23 GeoCAP Annual Conference, Taormina, November / 27 Conclusions Differential correction improves accuracy of area measurement but results of this test showed a small improvement (0.75m buffer to 0.50 m buffer) More tests needed -> we are waiting for validation test results from MS

24 GeoCAP Annual Conference, Taormina, November / 27 Results on EGNOS implementation in 2009 EGNOS monitoring station: receiver and antenna placed on the roof of building 26b in JRC, Ispra (2005) EGNOS antenna What do we register? Logging data every 1s - difference between the reference position of the point and EGNOS corrected position (

25 GeoCAP Annual Conference, Taormina, November / 27 Graphical presentation of the statistics derived between 1 st January and 31 st August ,20 1,00 0,80 0,60 0,40 0,20 0,00-0,20-0,40-0,60-0,80 January February Varies from 0.14 to 0.33 m March April May June July August 4,00 Mean monthly biases of X coordinate [m], together with standard deviations [m] with EGNOS correction Varies from 0.49 to 0.94 m Mean monthly biases of Y coordinate [m], together with standard deviations [m] with EGNOS correction 3,00 2,00 1,00 0,00-1,00-2,00 February March April May June July August -3,00

26 GeoCAP Annual Conference, Taormina, November / 27 Conclusions Based on the collected data - EGNOS correction is available from 98,2 to 100% since 1/1/2009 Open service officially announced as available on 1 st October 2009 by EC

27 GeoCAP Annual Conference, Taormina, November / 27 Thank you!