[gdal-dev] Differences in the coordinates of the origin in tfw-file and GeoTiff

[Fischer, Andreas]

Dear list, 
while translating or warping rasterdata with gdal_translate or gdalwarp I experienced a difference in the origin of an image in the tags of the GeoTiff-header and the tfw-file. 
The header of my original image looks as follows: 

Driver: GTiff/GeoTIFF 
Files: C:\test\in.tif 
Size is 10000, 10000 
Coordinate System is: 
PROJCS["DHDN / 3-degree Gauss-Kruger zone 3", 
GEOGCS["DHDN", 
DATUM["Deutsches_Hauptdreiecksnetz", 
SPHEROID["Bessel 1841",6377397.155,299.1528128000009, 
AUTHORITY["EPSG","7004"]], 
AUTHORITY["EPSG","6314"]], 
PRIMEM["Greenwich",0], 
UNIT["degree",0.0174532925199433], 
AUTHORITY["EPSG","4314"]], 
PROJECTION["Transverse_Mercator"], 
PARAMETER["latitude_of_origin",0], 
PARAMETER["central_meridian",9], 
PARAMETER["scale_factor",1], 
PARAMETER["false_easting",3500000], 
PARAMETER["false_northing",0], 
UNIT["metre",1, 
AUTHORITY["EPSG","9001"]], 
AUTHORITY["EPSG","31467"]]Origin = (3406000.000000000000000,5703000.000000000000000) 
Pixel Size = (0.100000000000000,-0.100000000000000) 
[ ... ] 
Corner Coordinates: 
Upper Left ( 3406000.000, 5703000.000) ( 7d38'50.85"E, 51d27'18.40"N) 
Lower Left ( 3406000.000, 5702000.000) ( 7d38'51.81"E, 51d26'46.05"N) 
Upper Right ( 3407000.000, 5703000.000) ( 7d39'42.63"E, 51d27'19.00"N) 
Lower Right ( 3407000.000, 5702000.000) ( 7d39'43.58"E, 51d26'46.64"N) 
Center ( 3406500.000, 5702500.000) ( 7d39'17.22"E, 51d27'2.52"N) 

The tfw-file coming out using the creation option -co TFW=YES (gdal_translate -co TFW=YES C:\test\in.tif C:\test\out.tif) looks like this: 

0.1000000000 
0.0000000000 
0.0000000000 
-0.1000000000 
3406000.0499999998 
5702999.9500000002 

The GeoTiff-tags in this image (out.tif) is still the same as above. But amazingly there is a slight difference in x and y coordinate of approximately 5 cm between tfw and GeoTiff. This difference does occur the other way around too. For example creating a GeoTiff from a png image with a tfw-file I get the difference in the new GeoTiff-tags as well. 
I start with those values in the tfw-file ... 

0.0846596700 
0.0000000000 
0.0000000000 
-0.0846596700 
392000.0000000000 
5733000.0000000000 

... and get these in the GeoTiff: 

Origin = (391999.957670164990000,5733000.042329834800000) 
Pixel Size = (0.084659670000000,-0.084659670000000) 

As mentioned above, the coordinates for the origin are not the same, but the image didn't change. Does anybody know about this behavior? 
I would be glad to hear from you. 
Thanks so far and best regards 
Andreas

Im Auftrag 
Andreas Fischer 
Kreis Unna - Der Landrat
Zentrale Datenverarbeitung
Friedrich-Ebert-Straße 17
59425 Unna 
Fon 02303 27-4416
Fax 02303 27-2896

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