SQL-Server and MapServer

[Frank Warmerdam]

On 11/3/05, listuser HH <listuser at herzsys.de> wrote:
> About the performance etc. I can't give you a hint, sorry - but you get the geometry diplayed. I think very important is the amount of features which you will display. I only used it for some single features and this worked good. Perhaps Frank Warmerdam can tell a bit more also for the con's on the usage of WKT in OGR.

Folks,

Generally speaking table access via ODBC is not doing
spatial indexing, and so it can be slow to pull a few rows
out of a big table for drawing a small local region.

However, I am in the midst of some changes to the ODBC
driver to support spatial indexing, and translation of WKT and
WKB without going through the OGR VRT driver.  This work
is now in CVS and would make it so you could use a datasource
name like:

  ODBC:mydsn,tablename(wkt_geometry)

This would mean open DSN mydsn, and access only the table
named "tablename".  Use the column "wkt_geometry" as the
geometry.  It will be parsed as WKB if the column is BLOB or
WKT otherwise.

Also, the new spatial indexing support provides for fast spatial
queries if the table has columns named "xmin", "xmax", "ymin"
and "ymax" with the geometric extents of the geometry for that
row.   These columns should be indexed for optimal efficiency.

Anyone interested in trying this out should grab the CVS snapshot
of GDAL/OGR.

I would add that using a "select" statement in an OGR VRT file
is a very flexible approach in terms of what you can do, but it also
has some downsides in terms of performance - especially when
used with the current query support in mapserver which requires
refetches by feature id when working with the query results.  This
issue does not affect rendering though.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent