[postgis-users] PostGIS Raster: Spec. for WKT and WKB?

[Stefan Keller]

Salut Pierre, Hallo Peter

Many thanks for your explanations.

Pierre answered:
> >=> Do you mean by WKB that these formats are specified in public
> >accessible specs.?
>
>
> As I said: no. They are not specified in public. I wish there would have been a public spec to tell me how to store raster but there is not.

I'd like to understand and support this better:

1. You write "They are not specified in public.": But now they are at
least in the sense of "PostGIS WKB", aren't they?
Now there is the PostGIS documentation
(http://trac.osgeo.org/postgis/wiki/WKTRaster/Documentation01) as well
as the source code publicly available.

2. Wen you say "I wish there would have been a public spec to tell me
how": Do you mean that there code/encoding gives still much room fore
enhancements? This would be an opportunity to be discussed but it also
would mean that "PostGIS WKB" would'nt be stable.

Yours. S.


2010/10/13 Pierre Racine <Pierre.Racine at sbf.ulaval.ca>:
> Hi Stefan,
>
>>I'm aware of WKT and WKB in vector knowing OGC Simple Feature Spec.
>>I'm now wondering about the usage of the notion Well Known Text (WKT)
>>and Well Known Binary (WKB) for raster.
>
> There is no WKT, WKB standards for raster and there is no standard (that I know of) to store raster in a database. WKT raster borrowed the WKT, WKB concepts to provide a way to directly create and read raster stored in the database.
>
> You will find the specification for our WKB format in this document: http://trac.osgeo.org/postgis/browser/trunk/raster/doc/RFC2-WellKnownBinaryFormat
>
> No specifications for WKT have been defined yet even if it was planned originally and it gave WKT raster its names. Note that we renamed the type "PostGIS Raster".
>
> WCS defines ways to query coverage data in general (raster, vector, point cloud, etc...) but in no way tells you what should be a raster and how to store it. It should not be too complicated to implement WCS as SQL functions over WKT Raster.
>
>>What I understand from the PostGIS Raster project home page
>>(http://trac.osgeo.org/postgis/wiki/WKTRaster) that JPEG and TIFF
>>formats are supported.
>
> PostGIS Raster does not "supports" other raster formats. It is a format (or better a "type") in itself. We have a Python "converter" (or a "loader" in DB terminology) that convert (or load) raster from any raster format supported by GDAL (in read mode) to PostGIS Raster. In this sence, it "supports" all those raster formats.
>
>>=> Do you mean by WKB that these formats are specified in public
>>accessible specs.?
>
> As I said: no. They are not specified in public. I wish there would have been a public spec to tell me how to store raster but there is not.
>
>>=> How about the spec. of WKT raster?
>
> You will find the best description of PostGIS Raster in those pages:
>
> http://trac.osgeo.org/postgis/wiki/WKTRaster/Documentation01
>
> Hope this help.
>
> Pierre
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