[GIS] Tiff: How to calculate Tiff Tag ModelPixelScaleTag (field 33550) and Field 34735

gdalgeotiff-tiff

I have to manage a service which can return images in tiff format.

This service is requesting another WCS Service from which it receives the Image File without geo-referenced informations.

So i need to set those informations and particularly tiff Tag field 33550, 33922, 34735 & 34737.

With metadata from WFS service i can use the pootprint and the projection to calculate tiepoints & bounds…

i get field 34737 from my projection (string) ex: WGS 84 / Plate Carree (deprecated)|WGS 84|

i get field 33922 from the foot print (it seems to be always 0.000000,0.000000,0.000000,Upper Left X,Upper Left Y,0.000000

tag 34735: how to know the meaning of all those parameters?

ex: projection epsg:32662
1,1,0,7,1024,0,1,1,1025,0,1,1,1026,34737,35,0,2049,34737,7,35,2054,0,1,9102,3072,0,1,32662,3076,0,1,9001

ex: projection epsg:3857
1,1,0,7,1024,0,1,1,1025,0,1,1,1026,34737,25,0,2049,34737,7,25,2054,0,1,9102,3072,0,1,3857,3076,0,1,9001

how to calculate field 33550 (ModelPixelScaleTag). I supposed it should be based on bounds and pixel width and/or height of the image. But my results is a little bit different from what i should set. (in the wcf service i saved a tiff before and after projection, i used this image (TiffInfo) to check what i have to set in the second service).

Do someone could explain me how to manage & set those fields? (particularly field 33550 & 34735)

TIFFReadDirectory: Warning, Unknown field with tag 33550 (0x830e) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 33922 (0x8482) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34735 (0x87af) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34737 (0x87b1) encountered.
TIFF Directory at offset 0x8 (8)
  Image Width: 448 Image Length: 418
  Bits/Sample: 8
  Sample Format: unsigned integer
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Extra Samples: 1<assoc-alpha>
  Samples/Pixel: 4
  Rows/Strip: 4
  Planar Configuration: single image plane
  Tag 33550: 155.783428,155.783428,0.000000
  Tag 33922: 0.000000,0.000000,0.000000,-1824666.305496,1276523.665790,0.000000
  Tag 34735: 1,1,0,7,1024,0,1,1,1025,0,1,1,1026,34737,35,0,2049,34737,7,35,2054,

0,1,9102,3072,0,1,32662,3076,0,1,9001
Tag 34737: WGS 84 / Plate Carree (deprecated)|WGS 84|

Update – more details:

My problematic is:

In one hand I have the image file (stream) associated to a Segment comming from a WCS Service. This image has been reprojected (if requested), but i only get the image without any geo-referenced informations.

In Second hand I have meta-data for this Segment (coming from a WFS Service). Those meta-data include wktBounds, wktCenter, wktFootPrint of the segment in WGS84.

In third hand I have request information –> projection

At the moment when a user requests for tiff Image, the service works with WGS84 tiff Image and set following tifftags:

                        // Referring to TiffInfo need to set
                        // Tag 34264 - TiePoints used to georeference image file
                        // Tag 34735 - fixed value associated to WGS 84 spatial reference system
                        // Tag 34736 - Ellipsoïd/Spheroid associated to the spatial reference system
                        // Tag 34737 - Name of spatial reference system

                        if (tiePoints != null)
                        {
                            val34264[0] = tiePoints[0];
                            val34264[1] = tiePoints[2];
                            val34264[3] = tiePoints[4];
                            val34264[4] = tiePoints[1];
                            val34264[5] = tiePoints[3];
                            val34264[7] = tiePoints[5];
                            tif.SetField((TiffTag)34264, val34264);
                        }

                        short[] val34735 = { 1, 1, 0, 7, 1024, 0, 1, 2, 1025, 0, 1, 1, 2048, 0, 1, 4326, 2049, -30799, 7, 0, 2054, 0, 1, 9102, 2057, -30800, 1, 1, 2059, -30800, 1, 0 };
                        tif.SetField((TiffTag)34735, val34735);

                        double[] val34736 = { 298.257223563, 6378137 };
                        tif.SetField((TiffTag)34736, val34736);

                        tif.SetField((TiffTag)34737, "WGS 84|");

The result is that the browser download the geotiff image.

Now i'm trying to adapt this for other projections (3857 and 32662) and calculate TiffTag Fields based on the meta-data of the genuine segment.

Best Answer

If you need to know what these tags mean, there are a couple of documents on remotesensing.org here for 34735 and here for 33550. These seem to cover the meaning of the fields.

As for how to set them programatically, that depends on which language you're using.

The Geotiff wiki on osgeo.org has links to the spec and libraries for the Geotiff format.

Update:

The documents from rempotesensing.org have been moved to http://geotiff.maptools.org/spec/geotiff2.4.html and http://geotiff.maptools.org/spec/geotiff2.6.html

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