Conclusion
Accuracy obtained using LIECA SR 9400 single frequency GPS receiver measuring code or carrier phase is of the order of 10-15 meters in point positioning mode with 5 hours of observations. Accuracy of similar order is obtained at rover points also within distance of 2-3 kilometers for observations of 30 minutes.
- Due to limitation of single frequency LIECA receiver observations for more then 45 minutes are required for base-length of 5-10 kilometers for resolving ambiguity.
- The main source of error for single frequency receiver is ionospheric delay. Therefore, observations for base-length more then 10 kilometers could not be taken due to system limitation for compensating for ionospheric error
- It was possible to identify and
correct abnormal height observation due terrain familiarity
The desired accuracy of GPS observations can be obtained by appropriately taking care of following issues
- Selection of day and time of observation
- Duration of observation
- Selection of reference point and corresponding rover points
- Datum conversion
- Height conversion
Future Issues
- Develop GUI based interface for on line tracking of GPS data and converting it into ARC/INFO coverage
- Create base maps using GPS
observations
Acknoledgement
We are thankful to Shri A.R Dasgupta, DD SITAA for providing us opportunity to explore feasibility of using GPS data for NRIS project.
Table-1: Coordinates Derived Using GPS (WGS-84 Datum)
Point 17 is Considered as Reference Point for
Baseline Processing
| SR. NO. | LATITUDE | LONGITUDE | HEIGHT ABOVE
ELLIPSOID |
| 17 | 22 50 28.09682 | 73 40 24.38946 | 87.1877 |
| 08 | 22 48 08.85339 | 73 37 02.93546 | 69.3931 |
| 11 | 22 51 44.32849 | 73 37 37.03182 | 68.2053 |
| 13 | 22 54 36.81210 | 73 38 08.98172 | 65.8170 |
| 15 | 22 53 47.64277 | 73 36 01.11677 | 74.3100 |
| 50 | 22 51 44.11065 | 73 31 58.76126 | 51.1162 |
| 14 | 22 54 21.33026 | 73 37 24.27028 | 89.8122 |
| 16 | 22 52 56.72526 | 73 33 54.93078 | 71.5811 |
Point 3 considered as Reference Point for Baseline Processing
|
| SR. NO. | LATITUDE | LONGITUDE | HEIGHT ABOVE
ELLIPSOID |
| 03 | 22 47 01.64677 | 73 33 49.27532 | 54.8687 |
| 01 | 22 47 44.28205 | 73 30 09.98229 | 31.9430 |
| 05 | 22 47 16.51705 | 73 41 02.23118 | 98.4480 |
| 06 | 22 48 54.08300 | 73 33 18.23283 | 54.5433 |
| 07 | 22 47 08.08902 | 73 36 40.59074 | 63.9192 |
| 08 | 22 48 08.58790
| 73 37 02.80601
| 66.4169
|
| 09 | 22 45 11.27817 | 73 40 31.15743 | 84.8819 |
Consistency of GPS measurement is apparent for
point no. 8
Table - 2 Comparison of Coordinates in Everest Datum
The coordinates in first raw are from NRIS database
The coordinates in second raw are from GPS measurement
| SR NO |
LATITUDE |
LONGITUDE |
HEIGHT |
DIFF. IN LAT.(meters) |
DIFF. IN LANG. (maters) |
DIFF. IN HEIGHT(meters) |
| 03 | 22 47 00.292
22 47 00.885 | 73 33 52.524
73 33 52.481 | 116.00
110.04 | -17.77 | 01.27 | 5.96 |
| 05 | 22 47 14.915
22 47 17.722 | 73 41 04.103
73 41 04.701 | 155.00
153.42 | -24.20 | -17.94 | 1.58 |
| 06 | 22 48 52.992
22 48.53.125 | 73 33 20.955
73 33 21.492 | 100.00
110.13 | -3.99 | -16.08 | -10.13 |
| 08 | 22 48 06.375
22 48 07.706 | 73 37 05.374
73 37 05.685 | 121.00
121.74 | -39.94 | -9.29 | -0.74 |
| 09 | 22 45 09.741
22 45 10.702 | 73 40 34.750
73 40 33.678 | 135.00
139.44 | -28.96 | 32.15 | -4.44 |
| 13 | 22 54 35.190
22 54 35.249 | 73 38 10.065
73 38 11.753 | 130.00
122.50 | -1.77 | -52.39 | 7.5 |
| 17 | 22 50 27.251
22 50 26.968 | 73 40 27.362
73 40 26.922 | 140.00
142.88 | 8.50 | 13.17 | -2.88 |
| 50 | 22 51 43.538
22 51 42.856 | 73 32 00.678
73 32 02.159 | 95.00
107.34 | 20.44 | -44.41 |
-12.34 |
Differences are within Range of 10-15 meters because of Local Parameters
being used for conversion
Table -3 comparison of coordinates in WGS-84 datum
The coordinates in first raw are estimated using Geoid model and seven parameters of transformation for Indian region
The coordinates in second raw are from GPS measurement
| SR NO | LATITUDE | LONGITUDE | HEIGHT | DIFF. IN
LAT.(meters) |
DIFF. IN LANG. (maters) |
DIFF. IN HEIGHT(meters) |
| 03 | 22.78394
22.78389 | 73.56469
73.56368 | 70.750
54.868 | 5.5 | 108.54 | 15.88 |
| 05 | 22.78800
22.78792 | 73.68456
73.68395 | 109.84
98.448 | 8.64 | 65.55 | 11.39 |
| 06 | 22.81524
22.81498 | 73.55592
73.55499 | 54.772
54.543 | 27.54 | 100.01 | 0.23 |
| 08 | 22.80229
22.80245 | 73.61825
73.61748 | 75.806
66.417 | -17.71 | 83.37 | 9.39 |
| 09 | 22.75323
22.75313 | 73.67640
73.67532 | 89.803
84.882 | 10.91 | 111.29 | 4.92 |
| 13 | 22.91029
22.91002 | 73.63622
73.63571 | 84.915
65.817 | 29.27 | 54.65 | 19.09 |
| 17 | 22.75323
22.75313 | 73.67641
73.67372 | 94.881
87.187 | 30.78 | 68.69 | 7.69 |
| 50 | 22.86261
22.86225 | 73.53363
73.53285 | 49.798
51.116 | 39.20 | 83.59 | -1.32 |