Different technology available and
limitations are discussed in brief below.
Ground survey cannot be avoided to
build a foolproof record. Depending on
the constraints and ground conditions,
particular technology can be used.
Electronic Total Station Survey
Establishing control by traverse and later
distance measuring is done using the total
stations. This replaces the conventional
theodolite and chain measurements or
plane table traverse for establishing
control. Detail survey is done by digital
recording of data instead of FMBs of
conventional system. The data can be
downloaded, processed and records
created. This process is time consuming.
Global Positioning System
and Total Station
GPS is used for establishing control
points required for detail survey in an
area. This technique is replacement for
the theodolite and traversing method,
reducing the efforts and time required
for establishing stations and observation. However, clear sky view of about
15° over the instrument is essential
for tracking of the navigation
satellites. Diffi cult to use in jungle/
tree covered areas. Total station is
used for further traversing and detail
survey electronically, and process
in a computer medium. However
in this method, we get accurate
records after the entire process is
completed. Staged upgradation of
records using available records is not
possible. This is a time consuming process.
Photogrammetric survey
combined with GPS, Total
Station and ground checking
Aerial photo gives a pictorial ground truth
and is a proof of ground at the time of
photography for times to come. Digital
Aerial photographs on 1:25,000 scale are
suffi cient to prepare a base map on 1:5,000
scale. However, contiguous area of about
5000 sq km will be economical. For rural
area this should be suffi cient. In urban
areas where land value is of signifi cance,
we require measurement accuracy upto 5-
10cm in a plot of 6metres x 9 metres size.
In such areas 1:1,000 scale survey will
be required and aerial photo on 1:5,000
will be essential. GPS is used to establish
minimum ground control required for
photogrammetric survey. A base map will
be generated on 1:5,000 scale for rural areas
and 1:1,000 scale for cities which can be
taken to the ground for ground checking
and picking up attribute information.
The process can be done in two ways:
- Generation of line maps from aerial
photo: Using digital photogrammetric
technique, line maps can be created
which can be taken to ground for
incorporating cadastral information
and other topographical details.
This can be brought back to offi ce
and incorporated in the data base.
- Generation of orthophoto, incorporating
information on ground and then
creating digital data base: Ortho photos
give accurate base and true picture of
ground while in fi eld. Deployment of
persons on fi eld work can be done with
minimum time and simultaneous work
can be done both in offi ce and fi eld for
creating digital data base. (Figure -5)
Use of PC Tablet/ Palm top for detail
survey and data capture in field
The digital line maps prepared in
photogrammetry can be stored in PC
Tablet/ Palm top and taken to ground to
incorporate attribute information, down
load to computer and process to get
information desired. Certain amount of
post processing of data will be required.
Airborne Laser Terrain Mapping
This technology is very costly but
can be used in forest areas to get
accurate height. Certain amount
of post processing is required. |
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