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Design of Large Area Spatial Framework for National (Natural) Resources Information System
R K Goel
Head, Geomatics Technology Division
Space Applications Centre Ahmedabad – 380053
For the sustainable development and monitoring of natural resources ,
Indian Space Research Organization has started
a major program National (Natural) Resources Information System (NRIS). NRIS is
visualized as network of Computerized, Integrated (Spatial & Non-Spatial)
databases around GIS as core for handling Natural Resources, Infrastructure and
Socio-economic data at District, State and Center level. Design and
implementation of suitable mechanisms for sharing and transfer of data across
district, state and center nodes is of utmost importance for this program. India
being a large Geographic entity, design and implementation of large area spatial
frame work is a pre-requisite for realizing computerized mechanism which can
facilitate bottom-up and horizontal transfers and aggregation of data amongst
the various District, State and central nodes..
In order to test
different projection/coordinate system, controlled spatial features are created
in topomaps of extreme regions of India. These features are then projected at
corresponding district, state and center level. Results obtained for each
projection are compared in terms of distortions in area, perimeter and length of
the features with respect to the original values at district level. Projection
is accepted if distortions are less than the tolerance limits specified in NRIS
Standards Document [1].
This technical paper presents the results of a
systems study conducted and suitability of projection and co-ordinate system to
be adopted for creating large area spatial framework for NRIS node
network
Selection of Projections for the study
The projections
are created by projecting three dimensional surface of the earth on the surfaces
like plane, cone or cylinder and these surfaces are developed into a two
dimensional plane. Because of reduction in dimensionally and approximation of
the earth into planar, conical or a cylindrical surface geometric properties of
features like shape, area, scale and direction(angle) change and distortions in
all or some of the geometric properties are introduced depending upon the type
of projection.
Since the NRIS database has to be created at India level
covering large area , it becomes necessary that the projection system selected
introduces minimum or tolerable distortions in geometrical properties while
aggregating spatial data from district level to state level and from state level
to centre level. For this purpose , the projection systems having following
criteria are considered for the study.
Criteria for selecting
appropriate projection
- Suitability for creating seamless data base at all India level.
- Regional characteristics viz. east-west and north-south.
- Geometric properties viz. shape ,area ,scale and direction.
- Suitability for thematic and topographic analysis and presentation.
- Suitability for mapping at state level (medium area) and at center level
(large area).
- Suitability for data aggregation at state and center level.
Based
on above criteria three projection systems viz. Polyconic , Transverse Mercator
and Lambert conformal conic with two standard parallels are selected for the
study. The UTM projection is not selected because of its limitation due to its
Zonal characteristic to represent only 6 degree longitude by 8 degrees latitudes
area. The major properties of these projections as described in Map Projection
manual [2] are as follows:
Polyconic Projection : Created by
lining up infinite number of cones along central meridian where meridians are
complex curve and parallels are not concentric circles. But as a compromise
meridians/parallels are represented as straight line segments. It introduces
minimum distortions in shape , area, scale and direction near central meridian
and distortions increase with respect to. distance from central meridian. Local
angles are accurate along the central meridian. The scale along each parallel
and along the central meridian is accurate. It increases along the meridians as
the distance from the central meridian increases One reason for selecting this
projection is that SOI topographic maps are prepared using Polyconic projection.
Transverse Mercator Projection : This is a cylindrical ,conformal
projection. Cylinder is kept longitudinal along meridian instead of along the
equator. The central meridian is centered on the region to be projected
therefore all distortion are minimum along north-south direction because
meridians run north-south. Small shapes are maintained but larger shapes are
distorted while going away from the central meridian. Since UTM can not be
considered for representing entire India his projection is selected for the
study.
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