| Re: how to composite a mapcoord object using geographic coordinate(no projection) [message #87704 is a reply to message #87702] |
Mon, 24 February 2014 05:37   |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Jie Zhou writes:
> I have send you a geotiff file with geographic coordinate by email yesterday. Did you get it?
I did get this file. Here is what the GeoTiff structure in the file
looks like:
IDL> help, geotiff
** Structure <6bcac450>, 7 tags, length=104, data length=96, refs=1:
MODELPIXELSCALETAG
DOUBLE Array[3]
MODELTIEPOINTTAG
DOUBLE Array[6, 1]
GTMODELTYPEGEOKEY
INT 2
GTRASTERTYPEGEOKEY
INT 1
GTCITATIONGEOKEY
STRING 'IMAGINE GeoTIFF Support
ERDAS Desktop 2010 10.1.0.604
Projection Name = Geographic (Lat/Lon)
Units = degrees
GeoTIFF Units = dd'
GEOGRAPHICTYPEGEOKEY
INT 4326
GEOGANGULARUNITSGEOKEY
INT 9102
You can see that the map projection "information" is embedded into the
file in a non-standard way as a CGCITATIONGEOKEY string that has to be
parsed to pull out the information needed to read the data. In other
words, this file has to be handled in a completely different way from
"standard" GeoTiff files, which use GeoKeys to obtain information.
I think it would be easier to write a routine that reads these specific
files than it would be to make old code behave in an unnatural way.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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