[gdal-dev] AREA_OR_POINT vs GDALMD_AREA_OR_POINT

[Even Rouault]

Joaquim,

I'm confused by what you are actually trying to do.

GDALMD_AREA_OR_POINT is a #define that evaluates to "AREA_OR_POINT". The string 
"GDALMD_AREA_OR_POINT" however is nowhere used in GDAL.

Regarding the MEM driver, GDALMD_AREA_OR_POINT is just a random metadata item.
Some drivers will set GDALMD_AREA_OR_POINT to the GDALMD_AOP_POINT = "Point" 
value.
And the GTiff driver uses it to determine if it must apply a half-pixel shift 
between the GDAL convention and the GeoTIFF convention.

Even

> Hi,
> 
> I made GMT respect as far as possible the AREA_OR_POINT GeoTiff key
> for read/write, but ...
> 
> The following was silently ignored (GMT uses the MEM driver)
> 
> GDALSetMetadataItem(hDstDS, "AREA_OR_POINT", "Point", NULL);
> 
> so digging here and there I found about GDALMD_AREA_OR_POINT, and in
> fact this one is now taken into consideration
> 
> GDALSetMetadataItem(hDstDS, "GDALMD_AREA_OR_POINT", "Point", NULL);
> 
> 
> However, this implies that on reading I have now to test for both
> 
> GDALGetMetadataItem(hDataset, "AREA_OR_POINT", NULL)
> 
>   ---- AND ----
> 
> GDALGetMetadataItem(hDataset, "GDALMD_AREA_OR_POINT", NULL)
> 
> This means that other codes that pay attention to the AREA vs POINT
> thing will have to do both tests as well and if they do only the first
> one, GeoTiffs created by GDAL will have the problem ignored, and quite
> likely an error in coordinates will follow.
> 
> So the question is, why this name duplication (AREA_OR_POINT vs
> GDALMD_AREA_OR_POINT) and why GDALSetMetadataItem() ignores the
> AREA_OR_POINT key?
> 
> Thanks
> Joaquim
> 
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