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mapguy
phatsbbnlist at twcny.rr.com
Thu May 20 13:55:08 PDT 2004
A question on TRANSFORM and related matters. ALL files verified as much
as possible (`gdalinfo`, `ogrinfo` , GIS, etc):
I have some "init=epsg:26918" (UTM 18N GRS80 NAD83) rasters in a tile
and some "proj=latlong" ( decimal degree ... derived from UTM NAD 83
GRS80 I believe the metadata implies) data in a line shapefile. They
plot perfectly.
I have "init=epsg:32115" (New York State Plane, Transverse Merc with
false northings and eastings) rasters in a tile and the same shapefile
as above, both in its original projection and in a state plane
conversion using ogr2ogr. Things don't seem so perfect.
The shape file is roughly 1/4 the size and 150 miles or so SW (3 region
diameters essentially) of the place and size it should be, i.e.
surrounding the tiled state plane rasters, and the associated quadrangle
lines from plotting the tileindex shapefile as a vector layer. Either
projection of the shape file works if I set the projection parameters
correctly in the map file. Either disappears if I set the wrong projection.
the TRANSFORM doesn't seem to matter (though the online docs mention
both "ON/OFF" and "TRUE/FALSE" in different places, and I tried both)
Is there a reasonable explanation as to why these files are plotting
this way? I mean, do false northings and eastings have to be added as
PROJECTION block params, or something like that? Does/How does TRANSFORM
work "on the fly", i.e. is there more to it than NOT putting TRANSFORM
FALSE/OFF in a layer?
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