Town base mapping through very high resolution satellite imagery

Town base mapping through very high resolution satellite imagery


Prof. P Misra
Tel:(011) 4623106 (R)
[email protected]

Town Planning and allied professions have always been demanding suitable base maps as a prerequisite to any planning and what is more important these days – monitoring. If we take the count of Class A and B towns, hardly 100 towns have the proper base maps, which incidentally might not have been prepared on standard specifications. Another well-founded fear is that these maps will be generally out of date. What about the base-maps of the remaining towns? It is therefore imperative that we harness that technology which serves our purpose well. The technology should be accessible without much hassle about the security.

The major difficulty in the past has been that base mapping was related to the technology (ies) which depended on the aerial photography. Aerial photography is, unfortunately, not available easily due to the restrictions imposed by the security environment. The net result of this security has been that technology of aerial photography, photogrammetry, orthophoto mapping etc. has eluded not only the town-planning profession but the other disciplines as well. However, in the Govt. Depts. like Survey of India, National Remote Sensing Agency the application of photogrammetry , rectification of aerial photograph and orthophoto mapping (removal of geometric distortions from aerial photographs and setting etc. at desired scale of 1:5000 or 1:0000) we see some successful examples of base-mapping. We should not ignore the major advantage of photogrammetry through which elevations could also be picked up alongwith the planimetry.

Satellite imagery of 5.8 meters resolution of Indian Remote Sensing Satellite (IRS-IC and ID) has proved very useful for providing ‘first aid’ information sans ‘elevation’. A few well-informed town planners utilized this technology.

Utilization of High Resolution Satellite Imagery

The good news, indeed very good news, is that satellite imagery of 1 metre resolution is now available. It is ‘IKONOS’ imagery which is commercially distributed by Space Imaging Corporation, USA throughout the world. It is already announced that National Remote Sensing Agency (NRSA), Hyderabad will supply this imagery on 1 metre (panchromatic) and 4 metres (multispectral) resolution to users in India. Imagine the improvement in the resolution form 5.8 meters to 1 meter!

The resolution of 1 metre enables the imagery to be used for town base mapping (Refer Figure 1). The imagery is in digital form and can therefore be imported directly on the computer.

Department of Space of Government of India has also planned to generate imagery of 2 meters resolution by launching CARTOSAT, its own satellite, in 2001. The situation in 2001, therefore, will be very much conducive for intensive activity of producing base- maps and physical inputs including monitoring (change detection) in urban and rural environment.

Monitoring, Detection of Change and Updating.

The IKONOS product comes from the satellite which is orbiting around the world. It is therefore possible to procure imageries of two different time epochs. Once the imageries are procured in digital form, it is easy to use software like ERDAS-IMAGINE to make a quick comparison on pixel to pixel basis. The imagery is supplied by a private firm of USA by the name of Space Imaging Corporation. Since data from IKONOS is in digital form, the data can be transmitted on Internet. Thus a very fast technology of updating the base maps is now available to the planning community. What is true for IKONOS is also true for CARTOSAT. Besides, CARTOSAT will be inexpensive as compared to IKONOS.

Cost of Production of a Town Base Map

Factors which influence the cost are listed as follows:
Source of satellite imagery Cost of ImageryIKONOS and CARTOSAT of Dept. of Space (in 2001) Scale of Base maps will be kept as the same as that of a regular revenue(Patwari) map.1:4000 or 1:5000 Elevations on a Town Base Map will be Provided by establishing Bench Mark (BM) by spirit levelling on the ground. BMs will be established on a few main roads of the Town. This should be acceptable to the Planning Community. about 25 km of levelling on the main roads. A representative town of area of 5000 ha is assumed for determining the cost, terrain is assumed to be plain. Area of town 5000ha (7km x 7km)
Based on the above assumptions and gaining experience from the in house actual production of a job, the range of cost is likely to be: Rs.125 to Rs.175 per hectare

The actual cost will depend on the quality of imagery and the type of terrain. Thus a town-base map of (7km x 7km) town will cost 7 to 10 lakhs. Base map can also be prepared for a portion of a town, in case budget restrictions are applicable.

Concept of Orthophoto as Urban Base Mapping.
The above mentioned estimate of cost is valid for urban areas which are plain and devoid of undulations and hilly areas. For hilly areas there is another technology known by the name of Orthophoto. Orthophoto by definition is the photo/image from which geometric distortion e.g. tilt and relief displacements have been removed. Thus, it will be seen that technology is available for all types of terrain. What is needed now is the motivation to utilize that for the benefit of the planning community.

The technology based on high-resolution satellite imagery will be ideal – cost and time effective – for producing base-maps of towns, villages slum areas or unauthorized structures. Town Planning – Departments should take initiative at their own level to expedite – the production of base-maps. Their budget will now be able to get base maps for more towns.