[gdal-dev] Raster origin coodinates in file header

[Even Rouault]

Adrien,

> opening 2 rasters with different resolutions i noticed a shift.
> 
> Asking our imagery provider, i was told the origin coordinates they
> store in image header (JP2 files) are those of the top left pixel center.
> 
> GDAL reads origin coordinates as the top left pixel top left corner
> coordinates, as i'm used to.
> 
> 
> Of course, i fixed my problem, the hacky way, playing with
> gdal_translate a_ullr option, but:
> 
> How to deal with this?

Normally, if the image provider did its job correctly, GDAL should report a 
consistant georeferencing in its convention (top left corner of top left pixel 
is 0,0), doing half pixel shift if needed.

There are 2 ways of encoding georeferencing in JPEG2000:
- GMLJP2, which has a convention of center of top left pixel. GDAL adds a half 
pixel shift to translate into its convention
- GeoJP2 (GeoTIFF-in-JPEG2000), which in most cases, uses the pixel-is-area 
convention, which is the same as GDAL. In rare cases, it could be pixel-is-
center, in which case recent versions of GDAL (1.11 perhaps, 2.0 for sure), 
will translate to GDAL convention.

Both can be present in a same file, in which case GDAL will use GeoJP2 
contents.

So if you're seeing a half pixel shift, either there's a remaining bug in GDAL 
(not sure where), either the image provider didn't encode it correctly

> How not to worry about georeferencing each time i load a raster file?
> Is there any OGC recommendation about origin coordinates storage?

GMLJP2 mentions it. GMLJP2 v1 wasn't completely clear about that, but the 
language of GMLJP2 v2 has clarified it.

Even

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