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Title
Remote sensing for resources development and environmental management
Author
Damen, M. C. J.

Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
551
Application of stereo-terrestrial photogrammetric technique
to varied geoscientific investigations
N.K.Agarwal
Geological Survey of India
ABSTRACT : Stereo-terrestrial photogrammetry provides distinct advantages over conventional techniques in
large scale topographic and thematic mapping of selected areas. During last six years this technique has
been advantageously applied to various geoscientific investigations in the Geological Survey of India, impor
tant amongst them being the Nilgiris landslide investigation, Tamil Nadu; escarpment slope mapping of Supa
Dam, Karnataka; mapping of Coconut Island, off west coast, Karnataka; and mapping of a glacier in north-west
Himalayas.
The methodology consisted of taking terrestrial stereo-pairs from 'UMK-100' Camera; surveying of control
points with the help a theodolite or 'Distomat' and plotting of details on the Unviersal Anologue Stereo-plo
tter 'Topocart'. Topographic and photo-interpreted thematic maps of these areas were prepared on scales
between 1:500 and 1:2000, except for the glacier which was covered on 1:5000 scale. The experience obtained
in applying this technique in diverse terrains has helped in gradually selecting the most suitable methodol
ogy.
Results clearly demonstrate the potential of this advanced technique in large scale mapping, for a compre
hensive evaluation of selected areas with speed, economy and precision. Further, the technique offers exci
ting possibilities of digital terrain modelling for multitheme mapping by making use of 'Analytical Stereo-
-plotter'.
1. INTRODUCTION
Geoscientific investigations of project areas requi
re preparation of large scale topographic base
map and relevant thematic maps of the area. Norma
lly, this work is being carried out with the help
of conventional plane table or theodolite survey
technique.
Aerial photogrammetric mapping has already been
established as a powerful tool for preparation of
topogrphic base maps with speed, economy and preci
sion, and the potential of photo-interpretation
technique is increasingly being exploited for thema
tic mapping.
Terrestrial photogrammetry permits acqusition
of controlled stereo-photographs of selected areas
at the desired time. The stereo-pairs are used
for the simultaneous preparation of large scale
topographic base map and relevant thematic maps
of the area. Further, computer assisted analytical
stereo-plotters, which are making a breakthrough
in photogrammetric mapping, provide scope for simu
ltaneous digitization of topographic and thematic
data of the area. This in turn would make morphome
tric and thematic mapping, either separately or
in combination an easy proposition.
Terrestrial photogrammetry was introduced in
Geological Survey of India in 1978. Since then
this technique has been advantageously applied
to a variety of geoscientific projects involving
diverse terrains, varying from Coastal tracts to
high mountaneous regions. Some of the important
investigations in which this technique has been
applied include Nilgiris landslide investigation,
Tamil Nadu; escarpment slope mapping of Supa Dam,
Karnataka; geo-environmental study of Coconut Is
land, off West Coast, Karnataka; and mapping of
a glacier in Northwest Himalayas.
The experience obtained while applying the tech
nique in diverse terrains has progressively helped
in adopting the most suitable methodology.
2. METHODOLOGY AND INSTRUMENTS
The technique of terrestrial photogrammetry invol
ves establishment and survey of four to five control
points in the area; photography for obtaining ste
reo-pairs with the help of a terrestrial phorogra-
mmetric Camera unit; and finally map preparation
in the laboratory on a stereo-plotter.
In the present surveys, a wide angle terrestrial
photogrammetric plate Camera 'UMK-100' (plate size
13 cm x 18 cm) of 100 mm focal length was used
for photography. Survey of control points was
intially done with help of a theodolite and subse
quently by an electronic distance measuring unit
Distomat. Map preparation was undertaken on the
analogue stereo-plotter Topocart.
2.1 Control point survey and establishment
Establishment and survey of control points in
the area is an important part of the photograpmme-
tric survey. For an expeditious and accurate survey
of the control points an electronic distance measu
ring unit Distomat has been found to be highly
convenient and handy. The coordinates of the surve
yed points can be obtained instantaneously in
the field.
In case of present surveys two different types
of orientation systems were used, one for the
Camera and the other for the Distomat. However,
if the Camera and the Distomat can be mounted
on the same orientation system then the field
unit becomes quite compact. It is particularly
significant if the unit has to be transported
on head loads for survey in remote inaccessible
areas.
During application of the technique in different
areas various objects have been tried as control
points. Ultimately, it has been found that white
painted circles, of appropriate dimensions (Manual