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

[Fischer, Andreas]

Dear Even,
thank your very much for that explanation. And indeed, I'm very surprised that there is a kind of a suborder within a pixel!
But that leads me to another question: 
You are talking about GDAL conventions. That means looking on the GeoTiff tags with another program than GDAL would show different values of the coordinates as well? So it's not a matter of GeoTiff itself?
And do you know about the behavior of MapInfo Professional? Is it right, that MapInfo uses the same reference as GDAL?
And the most important question: Assume I have a GeoTiff, a tfw and a MapInfo TAB-file for the same image file. Is the displaying of the image always the same regardless of which kind of referencing information a GIS programms uses?
I would be glad to hear from you again.
Thanks and best regards
Andreas

-----Ursprüngliche Nachricht-----
Von: Even Rouault [mailto:even.rouault at mines-paris.org]
Gesendet: Freitag, 18. Dezember 2009 21:39
An: Fischer, Andreas
Cc: gdal-dev at lists.osgeo.org
Betreff: Re: [gdal-dev] Differences in the coordinates of the origin in
tfw-file and GeoTiff


Yes, this is always a bit surprising at the beginning. There's a 
half-pixel size shift between worlfile and GDAL conventions for the 
origin. wordfile origin is at the center of the topleft pixel, whereas 
GDAL origin is at the topleft corner of the topleft pixel. But GDAL 
takes care of applying the right shift when reading from or writing into 
worldfile.

Your 5cm shift is indeed half the pixel size in your example.

Fischer, Andreas a écrit :
>
> 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
>
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>
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