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Binary WKB data over Pgsql ODBC

From: "Erik Brenn" <erikbrenn(at)hotmail(dot)com>
To: pgsql-odbc(at)postgresql(dot)org
Subject: Binary WKB data over Pgsql ODBC
Date: 2001-07-17 08:34:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: 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 :)

Erik Brenn

Erik Brenn
Senior Consultant
Blom International

Registered Linux User #205570
     (Registered at:

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Subject: RE: ODBC speed problem
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