N K Agrawal
Geodesy and GPS Services,
United States Department of Defense has given to the world GPS for navigation, positioning and time determination continuously. U. S. Government had put in place intentional restrictions on access to its signals so that accuracy of the system is limited for security considerations. Earlier there was anti-spoofing as well as selective availability (SA) to restrict accuracy of the system. Selective availability has been lifted since May 2, 2000. Anti- spoofing however continues. Accuracy of horizontal position in point positioning mode with a single receiver is limited to 15 to 20 metres, since P-code is not available to civil users. With P-code we can get accuracy of 3 to 5 metres. It is however possible to get better than 1 metre accuracy in position (latitude and longitude) by simultaneously using 2 receivers in relative or differential positioning.
If U.S.A., the most powerful nation, has put restrictions for security considerations, it is appropriate that India should also have some restrictions for dissemination of its geo-spatial data. Quote from R. Ramchandran’s “Public access to geographical data” is: “It only stands to reason that India devise appropriate restrictions to prevent national security-related risks. Of course any such restriction should have a rational basis. Unfortunately in the context of geographical data, the restrictions are perceived to be without much logical basis.”
|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|
Nobody is fully aware as to what in fact is the Restriction Policy of the Government of India as no such consolidated document is available. If such a document is made available it will end all confusion. It is expected that the Government will soon come out with a comprehensive Restriction Policy document in respect of Geo-spatial data capture and distribution, and make it known to the public so that it follows the law of the land that is just and rational and works in the best interests of the country. Restrictions on geo-spatial data are being notified in piecemeal manner through departmental circulars and orders, which are unclear and incomplete. The following is the summary of various restrictions, as the author understands them:
- Topographical Maps: All topographical and geographical maps a) of areas between a line approximately 50 km from external boundary of India and the external boundary on scales 1: 1 million and larger north of 200 latitude; b) areas between a line approximately 50 km from Indian coast-line and the Indian coast-line south of 200 latitude and c) of outlying islands viz. Andaman and Nicobar, Lakshadweep, Minicoy and Amindivi on scales 1:1 million and larger are all restricted. All maps inside of these lines are unrestricted.
- Position data in latitude and longitude: Horizontal control data up to 1 minute of arc of latitude or longitude are restricted. It appears that in a subsequent order it was mentioned that better data can be given without any restriction but meaning of this has not been clear. Do we conclude that data even up to second place of decimal can be made available? This is open to scrutiny and should be clarified. The authorities may be able to explain this.
- Heights: Heights above mean sea level rounded off to 10 metres in restricted zone, and rounded off to 10 cm in unrestricted zone are not restricted. All others are restricted.
- Aerial Photographs: All aerial photographs are classified as secret unless advised to be graded top secret by the Air Headquarters, Air Force. It is learnt that some photographs as decided by the authorities are made available for educational purposes on payment by requesting Director Survey Air of Survey of India New Delhi.
- Export of Maps: Even unrestricted Survey of India maps of scales even smaller than 1:250,000 should not be exported.
- Satellite Imageries: All Satellite imageries of 10 metres and better resolution are restricted.
- Gravity Data: There are restrictions on gravity and magnetic data also. It is not clear as to what extent gravity values and gravity anomalies are restricted. Similar is the case with magnetic data. These will have to be ascertained by the authorities.
- Indian Grid Data and Maps with Indian Grid: Indian Grid is on Lambert Conformal Conic Projection. India is divided into 9 zones. These grids are superimposed on topographical maps which are in so called Polyconic Projection. Once this grid is superimposed on any map even of unrestricted area, the map is classified as restricted. All parameters and all data in rectangular coordinates (x, y or Easting, Northing) pertaining to these grids are restricted.
- Data from Independent Surveys: There appears to be no restriction on survey and supply of data in unrestricted zone by any government or private agency. Any map that is published has to be got vetted and cleared by the Ministry of Defence. Only authorities can throw more light on this.
- Digital Data: Most of the digitized data and maps are restricted. Orders have been recently issued and published regarding digital data. Refer to GIS Development of November-December 1998. Letter no. 2(5) 95 D (GS-3) of Government of India Ministry of Defence may also be referred in respect of maps in digital form.
- Data on WGS 84 Datum: All the abovementioned restrictions are for data in Indian Datum, for which reference surface is Everest Spheroid. Any data in WGS 84 appears to be totally unrestricted. Ministry of defence has authorized Department of Science and Technology, to have a separate series of maps on WGS 84 for unrestricted production and distribution with limited contents. Accordingly Survey of India is likely to publish such maps in WGS 84 on Universal Transverse Mercator Projection for civilian use. No latitude and longitude lines will be shown on such maps.
- GPS Receivers: There is no restriction on GPS receivers. One can freely own a GPS receiver or a number of GPS receivers. He is free to carry out survey and acquire desired data, analyze and disseminate the same in WGS 84.
|Policy on geophysical data should be thoroughly studied, discussed and made transparent. If there is any security perception it should be properly explained|
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.
States should be made responsible for all developmental surveying and mapping in their states. The states can have their own coordinate system
Conclusion and Recommendations
It is obvious that our infrastructure policy in surveying and mapping, security considerations and restriction policy should be thoroughly looked into and changed to suit the security as well as development of the country. The following recommendations are made: –
- Indian Geodetic Datum may be redefined immediately to be used for defence and scientific purposes.
- Zero order and 1st order coordinates in WGS 84 may be restricted.
- All maps and coordinates in Indian Geodetic datum may be derestricted. Map contents may be reduced suitably.
- Photographs of restricted zone should only be restricted. Others to be derestricted after removing vital installations.
- Deletion of places of vital defence importance from unrestricted maps may be continued.
- Digitized data of unrestricted maps should be made available on payment without any restriction. Copyright should be effectively enforced.
- Heights above MSL rounded off to 10 cm may be derestricted.
- Contours are approximately surveyed. It means the contours can have error of more than half the contour interval. Therefore there should be no restriction on depiction of contours on maps.
- Grids for use by the defence forces should be redesigned immediately. Present Indian grid should be abandoned and derestricted. In author’s opinion the design of existing grids is unsatisfactory from technical viewpoint.
- Maps should be produced in Transverse Mercator or Lambert Conformal Conic projection by suitably carving out zones and assigning required parameters e.g. standard parallels, central scale factor, central meridian, origin, axes, assumed values of origin etc. It is not advisable to use UTM for our maps as origins are at the equator. This makes values of northings very high especially in northern latitudes.
- Polyconic Projection being used in India for topographical maps be abandoned, as it is thoroughly unsuitable. It creates digitization, integration and compilation of maps.
- Policy on geophysical data i.e. gravity and magnetic values. Gravity anomalies etc. should be thoroughly studied, discussed and made transparent. If there is any security perception it should be thoroughly explained.
- GPS receivers should continue to be available without any restriction.
- Surveying and mapping infrastructure should get top priority and enough funds. States should be made responsible for all developmental surveying and mapping in their states. The states can have their own coordinate system, one for each state.
- Ramachandran R., Public access to Indian geographical data, Current Science, Volume 79, No. 4.25, August 2000.
- GIS Development, November-December 1998, Heading Nowhere, Rules on Map Technologies in India, Cover story.
- Agrawal N.K., Abandon Polyconic Projection, GIS India, Volume 7, No. 1, January 1998.
- Agrawal N.K., Data Capture, GIS India, Volume 10, No. 5, September-October 2001.