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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: projection of maps |
| Date: |
10/06/2002 10:20:14 PM |
| From: |
Jayachandran Mani |
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Hi listers,
I need some clarifications on the "projection" process
used by more people using the survey of India
toposheets for digitisation in India. It may be more
regional. I apologise for posting this in the list.
But I believe i will be getting clarified of my doubt
here.
SOI maps are normally in polyconic projection with
everest spheroid. But the maps will have only the
lat/lon values on it. Those who digitise the SOI maps
use the intersection of lat/lon grids as their TIC
points for projecting into real ground values. Here
the information provided to the GIS software is as
follows
input projection - geographical
output projection required - polyconic
spheroid - Everest
units - meters
central meridian - the central meridian value of the
project area
Is it correct. I understand geographical means the
real lat/lon value of the point. But as the map is
already in paper format, the source itself is a
projected (polyconic) map. then what is the use of
projecting a map which is already in the polyconic
projection again to a polyconic projection. It is
confusing for me. Is this process is only to get the
rectangular co-ordiantes alone.??.
Please clarify
Thanks for your support
Regards
Jay
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