[postgis-devel] Two questions about wktraster development

Jorge Arévalo jorge.arevalo at gmail.com
Wed Sep 23 03:36:53 PDT 2009


On Tue, Sep 22, 2009 at 3:11 PM, Mateusz Loskot
<Mateusz.Loskot at cadcorp.com> wrote:
> 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

Yes, that is.

>
>> Is it a good way of doing this? Temporarily, of course.
>
> Yes, it is as long as the out-db support is provided/ready.

Ok. Anyway, I did the change only for testing purposes

>
>> - 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.

Of course yes. So, I may change the rt_raster_serialize code to test
this feature.

Many thanks Mateusz!

Best regards,
Jorge

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