Hi, Is there one, valid and unambiguous interpretation about what the "origin" means in JPEG2000 OGC-GML style metadata?
<gml:origin> <gml:Point gml:id="P0001" srsName="urn:ogc:def:crs:EPSG::3067"> <gml:pos>320000.0000000000000 6953999.5000000000000</gml:pos> </gml:Point> </gml:origin> I have read from a mail by Frank Warmerdam that origin should mean the centre of the anchor pixel. However, it looks like one major software vendor has a different interpretation and places the corner of the corner pixel into the origin. >From the OGC documents I could only find a Public discussion paper https://portal.opengeospatial.org/files/?artifact_id=35653 which, if I understand it right, is giving the same advice than Frank. Excerpt: " g) The location of the origin of the ImageDatum should be the grid point in a corner of the rectangular array of pixel values, at the center of a pixel. [Best Practice] NOTE As stated in Clause B.3.5 of Topic 2, the anchorDefinition pixel is usually either the centre or a corner of the image. This document recommends that the origin be a corner of the rectangular array. Notice that the anchorDefinition is different from the pixelInCell, which specifies whether the origin is centered on a pixel or is halfway between pixel centers. This document recommends that the origin always be centered on a corner pixel" Now I have a few sample images which include either GeoJP2 georeferencing or JP2GML georeferencing and GDAL finds different extents for those. If JPEG2000 image contains both GeoJP2 and JP2GML boxes then GDAL seems to select the GeoJP2 one which is good in my case because for these images it gives the correct georeferencing. The JP2GML itself contains only the gml:RectifiedGridCoverage definitions for the image but I haven't been able to find yet anything about how the raster image pixels should be placed to suit the RectifiedGridCoverage. I did find that there there exists a gml:pixelInCell element which can be set to mean either cell corner or cell centre but as far as I understood JP2GML does not contain this element. Sometimes I wonder why those OGC publications are called as "standards". -Jukka Rahkonen- _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
