[geos-devel] WkbReader and Z-geometries

[Martin Davis]

The EWKB that JTS and GEOS implement is based on the PostGIS EWKB 
specification (which predates the SQL/MM spec, I think.)

I don't have a good reference for the PostGIS spec - it would be nice if 
there was one online somewhere (hint, hint).

It might be nice if JTS/GEOS supported the SQL/MM spec as well.  Do you 
have a reference available for the spec?

Martin

On 8/3/2011 4:19 AM, Oyvind Idland wrote:
> Hello,
>
> i am trying to read WKB chunks based on the iso SQL/MM part3 spec. 
> However, this doesn't seem to work.
>
> From the WkbReader source code doc:
> "This implementation supports the extended WKB standard for 
> representing 3-dimensional coordinates. The presence of 3D coordinates 
> is signified by setting the high bit of the wkbType word."
>
> Which extended WKB standard is being refered to here ?
>
>
>
> For example, In the SQL/MM spec, various point types are defined as 
> the following unsigned values (not hex):
>
> <wkbpoint>     1
> <wkbpointz>   3000001
> <wkbpointzm> 2000001
> <wkbpointm>   4000001
>
> However, in the WkbReader.cpp the following logic is used:
>
>     int typeInt = dis.readInt();
>     int geometryType = typeInt & 0xff;
>     ......
>     bool hasZ = ((typeInt & 0x80000000) != 0);
>     if (hasZ) inputDimension = 3;
>     else inputDimension = 2; // doesn't handle M currently
>
>
>
>
> Is there any plans to implement support for SQL/MM ?  (I can volunteer 
> for a patch, if desired)
>
>
> -- Oyvind
>
>
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