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Provision of precise GPS control for the proposed international airport at Nagpur, India
Checking of Integrated Adjustment of GPS & Total Station Traverses
The end-user carried out traverses using total station survey, based upon this GPS control. To check its accuracy, an integrated traverse adjustment was also done taking GPS points as a control points. The Geodetic as well as UTM coordinates were provided on WGS84 datum, with MSL heights.
Fig 2: Network Map of GPS control points
Table 1: Computed
Coordinates of the GPS Control Points
| Stn. Name |
Latitude
(Seconds only) |
Longitude
(Seconds only) |
MSL Height
(m) |
| GP01 |
25.619 N |
32.494 E |
306.4 |
| GP02 |
54.491 N |
57.315 E |
306.2 |
| GP03 |
47.976 N |
36.464 E |
302.1 |
| GP04 |
48.177 N |
16.022 E |
303.9 |
| GP05 |
15.504 N |
48.136 E |
298.5 |
| GP06 |
41.882 N |
32.281 E |
305.1 |
| GP07 |
06.772 N |
19.306 E |
299.5 |
| GP08 |
01.786 N |
51.994 E |
301.0 |
| GP09 |
32.912 N |
08.135 E |
308.3 |
| GP10 |
34.934 N |
43.631 E |
312.2 |
| GP11 |
10.594 N |
56.705 E |
309.8 |
| GP12 |
57.596 N |
15.354 E |
310.2 |
| GP13 |
22.025 N |
58.987 E |
312.0 |
| GP14 |
34.816 N |
28.369 E |
311.6 |
| GP15 |
36.941 N |
00.794 E |
305.6 |
| GP16 |
49.165 N |
27.363 E |
305.4 |
| GP17 |
21.783 N |
33.454 E |
315.5 |
| GP18 |
07.670 N |
03.180 E |
308.5 |
| GP19 |
14.279 N |
22.434 E |
315.3 |
| GP20 |
40.974 N |
00.366 E |
317.9 |
| GP21 |
51.648 N |
50.650 E |
313.9 |
| GP22 |
07.074 N |
23.305 E |
313.4 |
| GP23 |
14.775 N |
23.304 E |
309.7 |
| GP24 |
39.471 N |
03.389 E |
310.7 |
| GP25 |
08.174 N |
45.242 E |
314.6 |
| GP26 |
28.572 N |
11.396 E |
322.1 |
| GP27 |
18.057 N |
04.498 E |
319.8 |
| GP28 |
46.517 N |
53.340 E |
316.1 |
| GP29 |
33.825 N |
31.281 E |
303.0 |
| GP30 |
57.219 N |
44.194 E |
304.6 |
| BASE |
44.354 N |
19.829 E |
311.7 |
Methodology of Checking Work Carried Out
- The total airport area was surveyed by the end-user using three total station traverses.
- All the three traverses have been adjusted using standard software, which applies the Bowditch rule. For this, GPS points have been taken as fixed control points.
As an example, sample data from the adjustment of Traverse one is given in Table 2
Table 2: Adjustment of Traverse one: Sample Data
|
T1S1 - FIRST SEGMENT GP06 - GP28 |
|
STN. NAME
|
NORTHING (m)
|
EASTING (m)
|
MSL HEIGHT (m)
|
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GP6/T2
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2332042.214
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298347.370
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301.8
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T3
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2332052.441
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298532.865
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302.9
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T4
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2332281.378
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298617.345
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303.5
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T5
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2332554.647
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298765.853
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301.3
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T6
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2333404.221
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298996.942
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295.8
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T7
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2333477.454
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298779.080
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296.7
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T8
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2333883.459
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298844.940
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296.3
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T9
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2334089.185
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298758.273
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298.4
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T10
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2334354.290
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298511.314
|
299.3
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|
T11
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2334602.544
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298426.585
|
299.4
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T12
|
2334631.835
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298375.461
|
299.6
|
Suggestions & Conclusions
The GPS control work described here is probably the first of its kind, for airport survey. Many valuable lessons were learnt from this work. Some of the conclusions and suggestions for future work are:
- The methodology adopted, of taking one base station and using the triangular network method, is found to be very much suited to this work.
- It would have been sufficient to use single frequency receivers for this type of work.
- The observation time adopted here, i.e. approximately 30 min. appears to be the optimum for such work.
- To carry out field checks to test accuracy of traverse stations from the GPS control points, about 4-5 consecutive traverse stations (not including GPS points) should be selected in each of the traverses, and adjustment of the total station traverse should be carried out. Using the given co-ordinates of the starting and closing stations as fixed points, co-ordinates of the 2 or 3 intermediate stations should be computed and compared with their co-ordinates provided. About 90% of the co-ordinates should agree within the specified accuracy limits, as per standard survey testing procedures.
- For checking the drawings prepared based on such control work, and the details in these drawings, co-ordinates/locations and heights of few well-defined points, as read from the drawing (softcopy or hardcopy) should be verified on ground. About 80% of the points thus checked should fall in the 1 meter accuracy level required for the 1:1000 scale drawing, as per standard survey & mapping testing procedures.
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