[gdal-dev] AREA_OR_POINT vs GDALMD_AREA_OR_POINT
Joaquim Luis
jluis at ualg.pt
Thu May 29 12:58:36 PDT 2014
> It's a pity that the original
>
> > registration type is not preserved in GDAL so we could respect it.
>
> Is not preserved : through which operations ?
>
Through some form of metadata that would inform us that:
"Although I'm reporting cell corner coordinates this file was
originally using cell center" (example case: Golden Software, AKA Surfer
format)
> > So let me repeat one of my previous questions, why was this ignored?
>
> >
>
> > GDALSetMetadataItem(hDstDS, "AREA_OR_POINT", "Point", NULL);
>
> What do you mean by "ignored" ? Self-contained reproducable use case
> please ;-) I don't read in your mind.
>
Sorry that you can't.
I can't refer to a 5 liner example so I'll have to show some printings.
When I use
GDALSetMetadataItem(hDstDS, "GDALMD_AREA_OR_POINT", "Point", NULL);
----- From GMT convert from netCDF to GeoTiff -----
grdreformat smt.grd lixo_MD_Pt.tiff=gd:GTiFF
Now gdalinfo shows "GDALMD_AREA_OR_POINT=Point"
gdalinfo lixo_MD_Pt.tiff
Driver: GTiff/GeoTIFF
Files: lixo_MD_Pt.tiff
Size is 256, 256
Coordinate System is `'
Origin = (-128500.000000000000000,127500.000000000000000)
Pixel Size = (1000.000000000000000,-1000.000000000000000)
Metadata:
GDALMD_AREA_OR_POINT=Point
<================================================
Image Structure Metadata:
COMPRESSION=DEFLATE
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( -128500.000, 127500.000)
Lower Left ( -128500.000, -128500.000)
Upper Right ( 127500.000, 127500.000)
Lower Right ( 127500.000, -128500.000)
Center ( -500.000, -500.000)
Band 1 Block=256x8 Type=Float32, ColorInterp=Gray
Min=-5000.000 Max=-1249.000
Minimum=-5000.000, Maximum=-1249.000, Mean=-4941.563, StdDev=395.981
NoData Value=nan
Metadata:
STATISTICS_MAXIMUM=-1249
STATISTICS_MEAN=-4941.5626603216
STATISTICS_MINIMUM=-5000
STATISTICS_STDDEV=395.98068901299
However, if I do instead
GDALSetMetadataItem(hDstDS, "AREA_OR_POINT", "Point", NULL);
grdreformat smt.grd lixo_MD_Pt2.tiff=gd:GTiFF
Than gdalinfo shows nothing in what regards the AREA_OR_POINT metadata.
This is what I was referring as "Ignored"
gdalinfo lixo_MD_Pt2.tiff
Driver: GTiff/GeoTIFF
Files: lixo_MD_Pt2.tiff
Size is 256, 256
Coordinate System is `'
Origin = (-128000.000000000000000,127000.000000000000000)
Pixel Size = (1000.000000000000000,-1000.000000000000000)
Image Structure Metadata:
COMPRESSION=DEFLATE
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( -128000.000, 127000.000)
Lower Left ( -128000.000, -129000.000)
Upper Right ( 128000.000, 127000.000)
Lower Right ( 128000.000, -129000.000)
Center ( 0.000, -1000.000)
Band 1 Block=256x8 Type=Float32, ColorInterp=Gray
Min=-5000.000 Max=-1249.000
Minimum=-5000.000, Maximum=-1249.000, Mean=-4941.563, StdDev=395.981
NoData Value=nan
Metadata:
STATISTICS_MAXIMUM=-1249
STATISTICS_MEAN=-4941.5626603216
STATISTICS_MINIMUM=-5000
STATISTICS_STDDEV=395.98068901299
> $ python
>
> Python 2.7.3 (default, Feb 27 2014, 19:58:35)
>
> [GCC 4.6.3] on linux2
>
> Type "help", "copyright", "credits" or "license" for more information.
>
> >>> from osgeo import gdal
>
> ds =>>> ds = gdal.GetDriverByName('Mem').Create('', 1, 1)
>
> >>> ds.SetMetadataItem('AREA_OR_POINT', 'Point')
>
> 0
>
> >>> ds.GetMetadataItem('AREA_OR_POINT')
>
> 'Point'
>
> >
>
> > > 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
>
> > > >
>
> > > >
>
> > > >
>
> > > > ----------------------------------------------------------------
>
> > > >
>
> > > > This message was sent using IMP, the Internet Messaging Program.
>
> > > >
>
> > > >
>
> > > >
>
> > > > _______________________________________________
>
> > > >
>
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>
> > > >
>
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>
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>
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>
> > >
>
> > > Geospatial professional services
>
> > >
>
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>
> --
>
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