| Associating GeoTiFF tags with basic Mercator projection parameters? [message #74177] |
Mon, 03 January 2011 21:07 |
BLesht
Messages: 89
Registered: March 2007
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I've been through the GeoTiFF threads here and, as often advised, have
tried to make sense of the GeoTiFF standard (http://remotesensing.org/
geotiff/spec/geotiff6.html#6.3.3) without success. I'm hoping that
someone with knowledge of using IDL to write GeoTiff files can give me
some help with the following problem.
I have a set of images that were created by transforming satellite
data onto a basic (single standard parallel at the equator) Mercator
projection. The projected images were created using IDL with a
minimal set of parameters; I know the size of the image (pixels,
lines), its geographic limits, the central meridian, and that it is
isotropic. Here is a header dump of the mapped files (which are hdf).
Sample:Projection Category = "IDL" ;
Sample:Projection Name = "Mercator" ;
Sample:Limit = 38.8744010925293, -92.41079711914062,
50.60269927978516, -75.86920166015625 ;
Sample:Projection ID = 9 ;
Sample:Latitude Center = 0. ;
Sample:Longitude Center = -84.13999938964844 ;
Sample:Rotation = 0. ;
Sample:Position = 0., 0., 1., 1. ;
Sample:Isotropic = 1 ;
Sample:Scale = 0. ;
Sample:Central_Azimuth = 0. ;
I do some manipulation of these files in my code and need to create
output mapped images of an extracted region in the form of GeoTiFF
files that can be read by ArcMap. The problem is that I seem to
unable to find the correct set of GeoTiFF tags to accomplish this.
For example:
g_tags = { $
ModelPixelScaleTag: [0.016153906d, 0.011453418d, 0d], $
ModelTiepointTag: [0, 0, 0, -84.813, 46.580, 0.], $
GTModeTypeGeoKey: 1, $ ; Projected
GTRasterTypeGeoKey: 1, $ ; Pixel represents
area
GeographicTypeGeoKey: 4326, $ ; WGS84
GeogLinearUnitsGeoKey: 9001, $ ; meters
GeogAngularUnitsGeoKey: 9102, $ ; angular degree
ProjCoordTransGeoKey: 7, $ ; Mercator
ProjNatOriginLongGeoKey: -84.13999d, $
ProjNatOriginLatGeoKey: 0.0 $
}
WRITE_TIFF, tif_name, new_comp_image, /FLOAT, GEOTIFF=g_tags
Produces files that "lack spatial reference data" when read by
ArcMap. I'd sure appreciate some guidance - maybe there is a better
way to accomplish this?
Thanks.
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