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
If yes, then why can’t we update it?
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
Before I comment on this, let us review briefl y the broad classifi cation
• 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.
Jawahar Lal Nehru National Urban Renewal Mission
Mapping thermal potential
Cartography enabled technology
Mission for cartographers
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
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
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: –