A typical output from geotiflib mey look like this:

    Version: 1
    Key_Revision: 1.0
       ModelTiepointTag (2,3):
          0                0                0
          1547250          5415950          0
       ModelPixelScaleTag (1,3):
          100              100              0
      GTModelTypeGeoKey (Short,1): ModelTypeProjected
      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
      GeographicTypeGeoKey (Short,1): GCS_DHDN
      GeogAngularUnitsGeoKey (Short,1): Angular_Degree
      GeogEllipsoidGeoKey (Short,1): Ellipse_Bessel_1841
      GeogSemiMajorAxisGeoKey (Double,1): 6377397.16
      GeogSemiMinorAxisGeoKey (Double,1): 6356078.96
      GeogInvFlatteningGeoKey (Double,1): 299.152813
      ProjectedCSTypeGeoKey (Short,1): Unknown-31468
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter

PCS = 31468 (name unknown)
GCS: 4314/(unknown)
Ellipsoid: 7004/(unknown) (6377397.16,6356078.96)
Projection Linear Units: 9001/metre (1.000000m)

Corner Coordinates:
Upper Left    ( 1547250.000, 5415950.000)
Lower Left    ( 1547250.000,  941650.000)
Upper Right   ( 7186450.000, 5415950.000)
Lower Right   ( 7186450.000,  941650.000)
Center        ( 4366850.000, 3178800.000)

From what I understand ModelTiepointTag will tell me where in an actual map the pixels it identifies are located so in this case pixel 0,0 should be at 1547250, 5415950 (what values are these exactly?).

ModelPixelScaleTag will give me a relation about the images scale in real life. But what exactly do these values mean, and how do I extract a useful value from them (eg this distance in my image is these many meters in real life)?

Corner Coordinates is quite easy to understand, but again I dont know what do those values represent. Can I convert them to latitude longitude values?

If the above was too long, then basically what interests me is to be able to understand how can I correlate the values on the image with the actual world values they represent.

  • This information: GeographicTypeGeoKey (Short,1): GCS_DHDN; GeogEllipsoidGeoKey (Short,1): Ellipse_Bessel_1841; ProjLinearUnitsGeoKey (Short,1): Linear_Meter, seem to indicate that the GeoTIFF Coordinate Reference System could be this, which is a meters projection. This link also has explanations about how to extract more information about the GeoTIFF including the latitude and longitude coordinates. – TsvGis Sep 1 '15 at 22:15
  • The GeoTiff specification is remotesensing.org/geotiff/spec/geotiffhome.html the spatial reference information is a bit hard to understand - there's lots of possible keys that can be stored... although the software you're using says PCS = 31468 (name unknown) it is actually a known spatial reference spatialreference.org/ref/epsg/31468 which may be identified by other software like Esri or QGIS, it's just a little obscure or specific... – Michael Stimson Sep 1 '15 at 23:07
  • Interestingly enough PCS code does not appear in the list ftp.remotesensing.org/geotiff/tables/horiz_cs.csv but the GCS that it's based on does: 4314,DHDN,,,,Germany - onshore,geographic 2D,6314,8901,North,East,Lat,Long,,9108,,,1995-06-02 00:00:00,,EPSG,, which could be why the projection is parameterized rather that being just an EPSG code. – Michael Stimson Sep 1 '15 at 23:18
  • The links, especially the one on listgeo are very interesting. What I still cant understand is the transformation between actual distances and image distances. Even if geotifflib can do it, I want to understand how to do it myself. – ealiaj Sep 2 '15 at 20:05

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