[gdal-dev] Re: [SoC] GDAL WKTRaster weekly report #9

Frank Warmerdam warmerdam at pobox.com
Wed Jul 29 01:14:15 EDT 2009

Jorge Arévalo wrote:
> Hello,
> Here, the report:
> http://www.gis4free.org/blog/2009/07/26/gsoc-09-weekly-report-9-1707-2407/
> And here, the project page: http://trac.osgeo.org/gdal/wiki/WKTRasterDriver


The progress looks good. You mentioned adding overviews tables as
subdatasets of the general dataset.  This isn't the usual way of
representing overviews which should be accessable via GetOverview() on
the GDALRasterBand.  Was this aspect done as well?

Is there any mechanism currently for creating overviews?  How have
you been testing overviews?

Under DOUBTs you ask what happens if the bounding box of a block
does not match any real block in the table, what should happen.  In this
case IReadBlock() should fill the buffer with the nodata value (zero if
nodata is not set).

You also mention a doubt about how to handle the 16BF type, which is
apparently "16-bit float".  I have never seen such a thing before and I'm
not sure why it is part of the WKTRaster specification. I would suggest
removing it.

However, if we wanted to support it (and you could figure out what it
actually is), then I think it would be most appropriate to transform it
into a 32bit float as it is read in IReadBlock().  Presumably the full
range of a 16bit float could not be kept in a 16 bit integer.

Likewise, 1BB, 2BUI, and 4BUI values (if supported) should be
translated on the fly into GDT_Byte values.  However, there is a special
NBITS metadata item in the IMAGE_STRUCTURE metadata domain that can
be set in these cases to represent the special nature of the image data.
Likewise there is a special value to indicate signed eight bit integers.
These values are discussed in:


However, I consider implementation of these esoteric types optional given
the relatively limited time remaining.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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