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GPS-Security and Restriction
GPS Receivers, Security and Restriction Policy
We shall examine restrictions on various data in connection with GPS only. We can get position of any point through GPS observations in a few seconds in latitude, longitude and height above WGS 84 ellipsoid, in WGS 84 datum. The horizontal accuracy with single GPS receiver in stand-alone mode of position is 15 to 20 metres. This means that we can get accuracy of better than 1 second of latitude or longitude. There is however difference between coordinates in Indian system and WGS 84. Transformation parameters are needed to convert coordinates of one system into another. Approximate transformation parameters have been estimated by the Defense Mapping Agency (DMA) of USA. These are integrated with each GPS receiver. We can therefore obtain coordinates in Indian system also with GPS with reduced accuracy but yet up to nearly 20 to 25 metres in most of the cases. It is seen that in most of the cases the coordinates obtained by even hand-held GPS receivers in Indian system vary by not more than 30 metres. The difference may however be even up to 100 metres in the North Eastern region of India. Accuracy of Coordinates of N-E region of India in Indian system, as they are now available is open to question. We can therefore safely conclude that the difference in coordinates between those obtained by GPS receivers in Indian system and those already existing in Indian system does not exceed 30 metres in most cases. It is clear that position can be obtained with GPS receiver to the accuracy of better than 1 second of latitude or longitude in Indian system. We thus see that this is in direct confrontation with restrictions mentioned in previous paragraph under (1) Topographical maps, (2) Position data in latitude and longitude and (12) GPS Receivers. (2) is completely ridiculous as I minute of arc represents nearly 1800 metres. Where do we go from here? Should we restrict import and use of each and every GPS receiver?
GPS Receivers and Indian Grid
Indian grid is in Lambert Conformal Conic Projection in 9 zones meaning 9 grids. The parameters of these grids i.e. latitude and longitude of origin, central scale factor, assumed (false) value of origin in x&y or E&N are restricted. These grids are superimposed on topographical maps of unrestricted zone also. Such maps are classified as restricted. Rectangular coordinates in these grids are also restricted. It is however seen that GPS receivers available in the market e.g. hand-held Garmin GPS-12 receiver can give coordinates in any of these grids anywhere in India and adjacent countries. This implies that these grids and their parameters are available to GPS manufacturers who have incorporated these into their GPS software so as to directly give coordinates in these grids. This is so as the grids were designed by the British, prior to our independence. The grids are available to the whole world including Pakistan. Actually Pakistan has also adopted the same grids applicable to their areas for their maps. The situation therefore appears to be dangerous. Should we change the grids? The answer is Yes. We have not been able to do this in more than 50 years and 4 wars and continuous proxy war. Let us do it now without any further delay. Further do we restrict the GPS receivers in view of the present orders on restrictions on data? The concerned authorities especially the Department of Defence and Department of Science and Technology should look into this aspect immediately.
Maps on WGS 84 Vs Maps on Indian Datum
We can say that WGS 84 represents a geocentric datum and very close to the assumption that center of WGS 84 ellipsoid coincides with C. G. of the Earth. It's center is estimated to be only + or - 2 metres away only. The assumption in case of Indian Geodetic System (Everest Spheroid) is that its center is nearly 1 km away from the C.G. of the earth. This ellipsoid is therefore not geocentric. Coordinates and maps on WGS 84 are therefore more important and vital. If we want to launch a missile across the continents, then if the launching station and target coordinates are in WGS 84, the result will be precise and accurate whereas if we have Indian system coordinates the missile is not likely to hit the target. This is because coordinates in different systems may vary by a few hundred metres to kilometres. It is therefore advisable that the coordinates in accurate system i.e. Everest Spheroid may be suitably derestricted immediately. In the meantime a new Indian Geodetic Datum may be defined. The project on " Redefinition of Indian Geodetic Datum " which was taken up around 1990 appears to have been shelved. It should be revived and completed within a specified period.
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