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General |
Site Prediction |
Interview |
Relevant Links
Spotting historical monuments and sites
Mapping of historical monuments and sites of Delhi using SPOT
satellite image
Methodology Adopted
- A definite systematic approach of study is required for such investigations
and in this study the following methodology has been followed.
- An interpretation key was prepared first for interpretation purpose.
- After preparation of the key, the SPOT image was visually interpreted
monoscopically and various monuments and historical sites were delineated on the
image using the interpretation elements- shape,size,pattern and tonal variation.
- All these delineated polygons were transferred to a base map (Fig 2).
- Based on the available aerial photographs of a small area, the sample area
was marked on the image and the base map.
- Aerial photographs were interpreted stereoscopically for comparison purpose,
that is, to find out the potentials and limitations of imagery vis-à-vis aerial
photos for such studies. In this process, a few more monuments were interpreted
which were not identifiable on the satellite image. The monuments and sites were
transferred to the base map and are shown by different cartographic symbols
within the photo coverage area marked with broken line (Fig-2).
- A limited field check was carried out to verify the accuracy of photo
interpretation, image analysis as well as of key.
- No statistical test was carried out to find the percentage of accuracy
because in such studies this has got very limited significance.
 Fig. 2: Spotting
Historical Monuments and sites
At the
identification, delineation and fieldwork stages various restrictions were taken
into account, like:
- On 1:25,000 scale SPOT image monuments on 75m x 75m size on ground can be
identified, i.e., 3mm x 3mm on image. But for delineation purpose (for
cartographic ease) 4mm x 4mm was kept. In the case of aerial photographs of
1:10,000 scale 50m x 50m can be identified easily with 3mm x 3mm delineation
unit.
- Various small structures within the built-up area were not considered
because they might be non-historical religious places and buildings in use.
- At the time of delineation of isolated structures, some excess area around
them was delineated for the purpose of cartographic ease.
- Buildings built by Britishers were excluded after field work because they
were considered as non-historical for this work and as part of designed and
planned cityscape except Coronation Pillar and its adjacent park. But any
building built on any historical place was taken as a historic site rather than
a building.
- After the final mapping, it was decided not to do the labelling because the
names of many lesser known and unknown monuments were not available
Discussions
- Four elements of image interpretation viz. pattern, shape, tone variation,
and size played a significant role in identification of monuments and sites.
- Shape of the objects combined with size played a significant role in
interpretation. Since people build things as square, rectangular, circular or
straight lines, features of this type having considerable size were identified
easily.
- Pattern or repetition is a characteristic of many man-made features. Since
cultural features consist of straight lines or other configuration, this helped
in interpretation and delineation of monuments.
- In the case of panchromatic image, tone variation is a very vital element
especially in built-up area. If the tonal variation with surroundings is poor,
then many buildings and sites may merge with the surroundings.
- Appropriate scale for identification of buildings and sites for SPOT
satellite image should be 1:10,000 or more. But keeping in view the inherent
weakness of spatial resolution and pixel size, it is not possible.
- Development of modern buildings and dense residential colonies near
historical monuments and sites creates difficulties in identification and
idealisation.
- Isolated monuments within built-up area were difficult to identify unless
the size of monuments was big enough. But when isolated monuments of smaller
size are located in open spaces or green areas properly landscaped, then
identification was rather easy.
Conclusion
Two inherent
properties of remote sensing image make the data derived from it extremely
useful in building a broad induction base:
- The wider environmental perspective afforded by remote sensing techniques
over more traditional ones on the ground surveys.
- The permanent nature of such imagery provides a fixed time space perspective
of ever- increasing historical value.
The role of large scale vertical
aerial photographs is undisputed in such studies because on 1: 10,000 under
magnification objects of 0.5 m can be identified, i.e, a spatial resolution of
1m is best suited while resolution and scale of the existing satellite images
for this kind of study pose problems. (Excerpts from Photonirvachak, Vol. No.
20, no. 2 & 3, June & Sept. 1992 )
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