The datum debate continues

We need Everest 2007 soon : Prof M N Kulkarni

In India, for topographical mapping, we are using an old Geodetic Datum (reference ellipsoid on which the coordinates: Latitude and Longitude are projected, and mapping is carried out), called Everest 1880, defined by the work of Col. George Everest (one of the greatest Geodesists, for whom the highest peak in the world is named). It is a local datum, best-fi tting for India (as in 1880), but not fi tting the Earth as a whole in the best possible manner.

Many countries in the world have been using their own local datums, and most have already redefi ned their datum, or have started using the global datum (fi tting the entire Earth): WGS84, defi ned by the Defense Mapping Agency (DMA), USA, which the GPS uses. Thus, all our Indian topogrphical maps (topo sheets) still use Everest1880 ellipsoid, and GPS gives coordinates on WGS84. If we use GPS and plot the coordinates observed on a toposheet, we will be mixing apples and oranges: the positions will differ by as much as 300 to 500 metres! Hence, the solutions are:

(i) Use WGS84 as map datum, and GPS or- (ii) Use the conversion factors (called transformation parameters) to convert GPS coordinates to Everest, and use with Indian topo sheets.

It is true that we are using on old datum, but it is being re-defined under a project launched by Survey of India (SoI) in the late 80s. I was in-charge of this project for 6 years (till I joined IIT Bombay). Similar project completed by USA for their datum: re-defined as North American Datum 1983 (NAD83) from NAD1927, used a very large manpower and huge funds, and took over 10 years. In SoI, we had just 4-5 persons, with a meagre budget for such project. This is an important project, and needs urgent attention of Government of India. We need Everest2007 soon!!

However, according to the recent map policy of Government of India, now
being implemented by the SoI, only the security classifi ed Defence maps
will use the old datum: Everest 1880, and all open maps, for developmental projects, general public use etc. will use WGS84 as datum. Thus, general public can use GPS with these maps. That should solve the major problem. Modernization, developmental projects, etc. will not be affected. The problem is in making these new WGS84 maps available to the public early, which SOI should take on priority. Till that time, the problems will remain. Another problem is that heights/contours on these new maps are not being made available easily to public, due to Defence restrictions. That is a setback, and needs to be removed: heights/contours are most essential in a map.

If yes, then why can’t we update it?
As mentioned above, the India Geodetic Datum is being re-defi ned. But the project has been relegated to the back-burner. It should be given top priority, required funding and manpower, and completed immediately. Changing all the maps to a new datum is a huge task, requiring huge resources, funds, manpower, etc. But it is important, and must be done on priority

Should we use WGS 84 or not?

Most countries in the world are using WGS84 as the datum for their mapping. It is a datum which is here to stay, possibly for a few decades, for mapping and navigational purposes. For scientifi c applications like eathquake research, plate motions studies etc., scientifi c datums called International Terrestrial Reference Frames (ITRF) are defi ned by the International Earth Rotation Service (IERS) every year (ITRF2005, etc.). But for mapping, navigation, developmental projects, infrastructure development, and most common applications, WGS84 is good enough.

The Universal Transverse Mercator Map Projection and Grid System (UTM), used most widely all over the world, is also the most scientifi c, convenient and digital mapping-compatible system, and should be used for these maps.

Dr Kumar says solutions are available, Do you agree?

Indian geodesists have the know-how and expertise to carry out these tasks. Of course, all help from expert agencies like National Geodetic Survey, USA; DMA, USA, and expert persons like Dr Muneendra Kumar is welcome and should be taken. Unfortunately, many of our Government departments like SoI do not make use of the expertise available outside their own Department, like experts in other scientifi c and academic organisations and Institutes, retired Geodesists, etc. Their contribution and advice would be of great help in putting these highly scientifi c tasks on the right track and in expediting them. Probably an eminent and young, dynamic Geodesist as Head of SoI would be able to provide the leadership and guidance required for these important national tasks!

Not advisable to stick to weak datum: LT GEN SURINDAR P MEHTA

Questions have been raised at various quarters whether the Vision invoked
by the President can be fulfilled by using 19th century Datum.

Before I comment on this, let us review briefl y the broad classifi cation
of Mapping /Cartographic effort required for various applications.
• Cartography for Global level planning and execution. This calls for most accurate techniques to depict the shape and size of the earth. Requires most accurate absolute positioning of points on globe to ascertain correct distance, directions, areas, volumes, essential for various global activities such as Global Warfare, Continental Drift, etc. Also involves very precise
measurements of International boundaries. There is the requirement of most precise control network based on well defi ned Datum.

• Cartography for Macro level planning and execution. Requires depiction of all major topographical details (both physical and manmade) relatively correct to enable macro level study and planning of land related activities. Topographical maps on scale 1:25000 to 1:250000 have been used. Relative accuracy is important and distance, area and volume can be computed within limited accuracy, generally acceptable for macro level planning. Any suitable cartographic projection with any reasonable datum can serve the purpose.

• Cartography for Micro level planning and execution. This requires all terrain data accurate in size and shape in relative correct position so as to get true distance, area and volumes for micro level planning and execution of land related projects. These are large scale maps of the small area of interest. Some of the Engineering projects ( such as Irrigation) , require study on map scale 1:5000 to 1:10000 and further detailed planning, design and execution on larger scale (1:1000 or even larger). Relative accuracy of positioning of details is the prime requirement and absolute positioning and well defined datum is not mendatory.
Let us now examine major inputs required for various requirements projected by the President.

Providing Urban Amenities in Rural Areas
Requires mapping on large scale (1:10000 or larger 1: 2000) for 7000 PURAS (6 lakhs villages / 2 lakhs panchayats) in 2 years time. Requires huge survey and mapping effort. It is advisable to collect terrain data based on the existing control network , rather than waiting for any new Datum defi nition

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.