[postgis-devel] Two questions about wktraster development

[Mateusz Loskot]

Jorge Arévalo wrote:
> Hello everybody,
> 
> During this summer, I took part in Google Summer of Code, developing
> the WKT Raster driver for GDAL. After the program, I'm going to carry
> on with the project. Just now, I'm testing 2 features I couldn't test
> properly during GSoC. These are out-db raster support and endianess.
> And I've a couple of questions:
> 
> - Out-db support: I modified the gdal2wktraster script to add out-db
> support [1]. I had to "hack" the WKT Raster extension code to allow
> out-db rasters too. I simply commented the lines 532-535 of
> $WKTRASTER_SRC/rt_pg/rtpostgis.sql file (out-db checking).

You probably mean these lines:

http://trac.osgeo.org/postgis/browser/spike/wktraster/rt_pg/rtpostgis.sql.in.c#L539

> Is it a good way of doing this? Temporarily, of course.

Yes, it is as long as the out-db support is provided/ready.

> - Endianess: I tried to insert raster data with different endianess
> than my machine, but when the INSERT was executed, the endianess was
> changed to the correct one. At which level does it happen? WKT Raster
> extension level, PostgreSQL level? I couldn't apply a "hack" here...

It is correct behaviour.
You insert data indirectly calling RASTER_in function:

http://trac.osgeo.org/postgis/browser/spike/wktraster/rt_pg/rt_pg.c#L260

The first byte of raster WKB stream indicates endianness.
This flag is used by WKB parser to read "real numbers" from WKB stream:

http://trac.osgeo.org/postgis/browser/spike/wktraster/rt_core/rt_api.c#L1865

Then object composed of "real numbers" is serialised
according to native properties of host machine:

http://trac.osgeo.org/postgis/browser/spike/wktraster/rt_core/rt_api.c#L2367

I hope it does make sense.

Best regards,
--
Mateusz Loskot
Senior Programmer, Cadcorp
http://www.cadcorp.com



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