Binary WKB data over Pgsql ODBC

Hi all,

We're running pgsql 7.1.2 on a Linux RH PowerEdge dual cpu box. I have a
number of AutoCad clients which I plan to setup reading/writing to the pgsql
server using VBA/rdo from AutoCad process space.

On the server I have installed PostGIS which I have tested libpq C-programs
with impressing speeds. Now I wish to use the pgsql ODBC driver to make the
link from our Win2k CAD systems. (VBA in AutoCad Map)

The PostGIS extension to pgsql have functions that can throw back WKB (Well
Known Binary) streams from the server.

I wish to do a query like this from my ODBC client:

select wkb_ndr(geo_column) from .... where ...

I see in the configuration window of the ODBC driver that unknown types can
be handled as LongVarChar data type. Since the binary data coming from
PostGIS would be unknown to the driver I assume it's going to throw back
LongVarChar to my client program. Is this correct?

Also, after posting this to the PostGIS mailing list I was informed about
some limitations on the size of text or LongVarChar data. Can someone
elaborate a little on this and perhaps enlighten me on what problems I'm
likely to meet with regards to this. And can I change such a limitation
myself if I recompile the driver, and what side effects will that give?

Note that I can do a select without the wkb_ndr() function, in which the
server will throw back WKT (well known text) strings which I would have to
parse on the client. If these strings are very long, will they be truncated
by the ODBC driver? If so, how can I find out the supported length?

It would be really nice if we could use the ODBC driver from Windows
applications to retrieve geometric information in binary streams, this would
open up for some true database enabled GIS applications on Windows.
Informix once wrote an ODBC driver for its spatial datablade, which was used
for example by MapInfo GIS clients. ArcInfo has done some similar things
towards Oracle Spatial (I assume they use ODBC).
Can we do this using Pgsql/ODBC soon, or is it perhaps possible already?

Comments are mostly welcome :)

regards,
Erik Brenn

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___________________________
Erik Brenn
Senior Consultant
Blom International

Registered Linux User #205570
(Registered at: http://counter.li.org)

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