The datum debate continues

Jawahar Lal Nehru National Urban Renewal Mission
Requires preparation of Base maps on large scale (1:2000 or 1:4000) with
contours at 1m interval for 63 large cities for proper planning and layout of
road network and utilities. Considering time limitations, terrain data may be acquired based on existing control network. As stressed by the President, all city administration agencies should use this base data for their applications, to ensure uniformity and avoiding wasteful duplicate effort. Survey of India should, however, examine the security aspect of this base map with heights 1m or less for free public use.

Disaster management
Existing topographical maps duly updated using aerial photographs and high resolution imageries will serve the purpose. Additional details, as required, can also be incorporated on the same maps.

Mapping thermal potential
Existing topographical maps duly updated can serve base maps for superimposition of thematic information of thermal potential to be collected by specialized agencies.

Cartography enabled technology
It is heartening to note that India has its own CARTOSAT for high resolution terrain data. This will generally meet the requirements of topographical maps and DEM of 8m accuracy. This will be useful for Feasibility studies, but will need additional survey effort for detailed designs and layout of infrastructures and utilities.

Mission for cartographers
President has asked for creating a network for all organizations, which should essentially be carried out by the government (DST).Mapping of large scale maps for PURA and JNNURM in about 2 years time is a real challenge for Survey of India. Uploading of digital data on the web site will be a dream come true, considering the hurdles to be encountered from various agencies.

Special resources will have to be catered for updating existing base maps required for Disaster Management and Wasteland Mapping.President has expressed the need for training and building a human resource team, which can face the challenges of the 21st century. This involves imparting of indepth knowledge of geodetic science and allied disciplines like digital cartography, GIS. In addition to updating courses in STI, Hyderabad, there is the requirement of establishment of more such Institutions in India as well as continuous interaction and collaboration with prestigious institutions of developed countries.In addition , major users, engineers, geographers and scientists involved in geoscience need to be educated in the basics of these fundamental disciplines so that they can utilize terrain data usefully.

Need for review of datum
Any useful mapping has to be based on accurate control network. India has vast network of ground control points based on datum weak in defi ition but good enough for relative positioning of vast amount of terrain data required for development projects in a short time frame. India has a vision of transforming itself into a developed nation before 2020 and has to face the cartographic challenges of 21st century. Most precise well defi ned coordinate system is a requirement for global warfare as well as for carrying out research in disciplines like seismic studies, continental drift etc. I am sure that SoI will take appropriate steps and adopt most suitable well defi ned datum to meet these challenges. It is also not advisable to have two different datum, projections and grid systems in 2 series of maps. These will create operational problems, besides being costly proposition. Moreover, it is not advisable to stick to weak datum (Everest) for Defense Series Maps when we want to operate on global platform.

Redefi nition of Indian datum is necessary :- N K Agarwal

Firstly let us call the datum as Indian datum based on Everest Spheroid 1830. Redefi nition of Indian datum is necessary and should be done at the
earliest. I understand that Survey of India has taken it up, but its status is not known. Status should be put on the SoI website. A geocentric reference datum is necessary for defence applications and research including study of plate movements, crustal movements, subsidence, rise in sea level etc. A new vertical datum is also necessary. I understand that SoI has initiated action to defi ne a new vertical datum.

Why say, GPS accuracy? We should defi ne accuracy in parts per million or simply zero, 1st, 2nd, 3rd, or 4th order accuracy. GPS is capable of giving zero order (better than 3 to 4 parts per million) as well as 4th order (less than 1 in 5000) accuracy. These accuracies are achievable with other instruments and techniques as well. Further our maps are designed very well and with adequate accuracy and need not be linked to GPS accuracy. Only the map projection for topographical maps, polyconic projection that is being used in a way, assuming no distortion and curves is not correct and creates diffi culties in compilation and digitization.

Now let us see as to what the honourable President has mentioned in his VISION. These are as follows: –
1. PURA,
2. JNN Urban Renewal Mission,
3. Disaster management,
4. Flood and Water management,
5. Flood control through layered wells,
6. Six missions for cartographers.
Most of the above can be achieved even with the present Indian datum and vertical datum for MSL heights.

Some problems may however arise in respect of defence applications, research and high-end civil applications like crustal movements, interlinking of rivers etc. This means that we have got to change over to a new geocentric reference datum, and a new vertical datum anyway then why not do it now and produce all maps in the new datum. Most important for President’s vision are Redefi nition of Indian Horizontal datum as well as vertical datum, availability of horizontal and vertical control points of at least 3rd order accuracy at every 2 km, adoption of LCC or TM projection for maps by breaking India into a number of convenient zones for all types of mapping. All development mapping should become a state subject with a grid of their own on similar lines to SPCS (State Plane Coordinate System) for various states in USA. Main hindrance to Presidents vision comes from Restriction policy, confused map policy, lack of transparency, clear thinking, funds, and trained manpower.