High Resolution 1:10,000 scale Mapping Strategy of Multi ... - NDMA

handed system. ITRF is a set of points with their 3-dimensional Cartesian
coordinates and velocities, which realizes an ideal reference system, the
International Terrestrial Reference System. Each ITRF is identified by the digits of
the year as ITRFyy e.g. ITRF97, ITRF2000 etc. The latest is ITRF2005 which has the
epoch 1 st January 2000. For realization the different techniques are used: Very Long
Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Satellite Laser Ranging
(SLR), Global Positioning System (GPS) and Doppler Ranging Integrated on Satellite
(DORIS). Each has strengths and weaknesses - their combination produces a strong
multi-purpose Terrestrial Reference Frame (TRF). ITRF is the best geodetic
reference frame currently available. The GRS80 ellipsoid is recommended by IERS
to transform Cartesian coordinates to latitude and longitude.
India has an existing network of approximately 300 Ground Control Points (GCP).
This network is to be used in the image acquisition for the hazard mapping database
in this project. The number of stations directly realized by the geocentric geodetic
system is not enough for practical use. Worldwide there are several hundred realized
stations in ITRF and about twenty stations in WGS84. Therefore it is necessary to
increase the density of the local stations based on the given stations in each nation
or area.
GROUND CONTROL POINTS
Horizontal control points shall be set up as station points in a closed traverse
whenever practicable. If field conditions dictate otherwise, control points shall either
be tied to the traverse from two different stations or have the angles and distances
for single ties measured at least twice. Each control photograph shall be examined
carefully in the field to insure that the object described in the photograph is indeed
the corresponding object in the field.
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