I'm trying to understand GeoTIFF info, but not getting far. For instance, using listgeo
with one file I can get this output:
Geotiff_Information:
Version: 1
Key_Revision: 1.0
Tagged_Information:
ModelTiepointTag (2,3):
0 0 0
617632.387 5169109.1 0
ModelPixelScaleTag (1,3):
0.597164283 0.597164283 1
End_Of_Tags.
Keyed_Information:
GTModelTypeGeoKey (Short,1): ModelTypeProjected
GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
GeographicTypeGeoKey (Short,1): Unknown-4167
GeogAngularUnitsGeoKey (Short,1): Angular_Degree
GeogSemiMajorAxisGeoKey (Double,1): 6378137
GeogSemiMinorAxisGeoKey (Double,1): 6356752.31
GeogInvFlatteningGeoKey (Double,1): 298.257222
ProjectedCSTypeGeoKey (Short,1): Unknown-2134
ProjLinearUnitsGeoKey (Short,1): Linear_Meter
End_Of_Keys.
End_Of_Geotiff.
PCS = 2134 (name unknown)
GCS: 4167/(unknown)
Projection Linear Units: 9001/metre (1.000000m)
Corner Coordinates:
Upper Left ( 617632.387, 5169109.098)
Lower Left ( 617632.387, 5164958.209)
Upper Right ( 621797.608, 5169109.098)
Lower Right ( 621797.608, 5164958.209)
Center ( 619714.997, 5167033.654)
Now, I know that those corner coords are UTM, but does anything in the other tags tell me that?
Similarly, with a different projection, the same area gives me:
Geotiff_Information:
Version: 1
Key_Revision: 1.0
Tagged_Information:
ModelTiepointTag (2,3):
0 0 0
19198032.5 -5377596.2 0
ModelPixelScaleTag (1,3):
0.597164283 0.597164283 1
End_Of_Tags.
Keyed_Information:
GTModelTypeGeoKey (Short,1): ModelTypeProjected
GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
GeographicTypeGeoKey (Short,1): GCS_WGS_84
GeogAngularUnitsGeoKey (Short,1): Angular_Degree
GeogSemiMajorAxisGeoKey (Double,1): 6378137
GeogSemiMinorAxisGeoKey (Double,1): 6356752.31
GeogInvFlatteningGeoKey (Double,1): 298.257224
ProjectedCSTypeGeoKey (Short,1): Unknown-3395
ProjCoordTransGeoKey (Short,1): CT_Mercator
ProjLinearUnitsGeoKey (Short,1): Linear_Meter
ProjStdParallel1GeoKey (Double,1): 0
ProjStdParallel2GeoKey (Double,1): 0
ProjNatOriginLongGeoKey (Double,1): 0
ProjNatOriginLatGeoKey (Double,1): 0
ProjFalseEastingGeoKey (Double,1): 0
ProjFalseNorthingGeoKey (Double,1): 0
ProjFalseOriginLongGeoKey (Double,1): 0
ProjFalseOriginLatGeoKey (Double,1): 0
ProjFalseOriginEastingGeoKey (Double,1): 0
ProjFalseOriginNorthingGeoKey (Double,1): 0
ProjCenterLongGeoKey (Double,1): 0
ProjCenterLatGeoKey (Double,1): 0
ProjCenterEastingGeoKey (Double,1): 0
ProjCenterNorthingGeoKey (Double,1): 0
ProjScaleAtNatOriginGeoKey (Double,1): 1
ProjAzimuthAngleGeoKey (Double,1): 0
ProjStraightVertPoleLongGeoKey (Double,1): 0
End_Of_Keys.
End_Of_Geotiff.
PCS = 3395 (name unknown)
Projection Method: CT_Mercator
ProjNatOriginLatGeoKey: 0.000000 ( 0d 0' 0.00"N)
ProjNatOriginLongGeoKey: 0.000000 ( 0d 0' 0.00"E)
ProjScaleAtNatOriginGeoKey: 1.000000
ProjFalseEastingGeoKey: 0.000000 m
ProjFalseNorthingGeoKey: 0.000000 m
GCS: 4326/WGS 84
Datum: 6326/World Geodetic System 1984
Ellipsoid: 7030/WGS 84 (6378137.00,6356752.31)
Prime Meridian: 8901/Greenwich (0.000000/ 0d 0' 0.00"E)
Projection Linear Units: 9001/metre (1.000000m)
Corner Coordinates:
Upper Left (19198032.501,-5377596.196)
Lower Left (19198032.501,-5383223.872)
Upper Right (19203679.883,-5377596.196)
Lower Right (19203679.883,-5383223.872)
Center (19200856.192,-5380410.034)
The tags 'tell me' this is WGS84 - but what are the coords? I'm trying to reliably extract positional data, but can't because I don't understand the what the output is telling me?
Answer
Here's an extremely dense but useful explanation of the GeoTIFF specification: http://duff.ess.washington.edu/data/raster/drg/docs/geotiff.txt
The PCS tag is the EPSG number of the projection coordinate system. GCS is the EPSG number of the geographic coordinate system. So your first file is in UTM 59S, with linear unit of meters. The second file is World Mercator, also with linear unit of meters. The cell size of both is ~0.597m. GeogAngularUnitsGeoKey is the unit of the GCS, and ProjLinearUnitsGeoKey is the unit of the PCS.
Hopefully that will get you started.
No comments:
Post a Comment