[Gdal-dev] ogr.py Intersect with wkbGeometryCollection

[Frank Warmerdam]

On 5/5/05, Ryan, Adam <ARyan at co.linn.or.us> wrote:
> The goal for me is to write a generic theme-on-theme spatial query method,
> where you would pass an ogrQueryLayer and an ogrSelectLayer with a
> selectList (of record indexes obtained from a previous query that likely
> involved mapscript and not ogr directly) and a method (for this test I just
> do an intersect) and a mode (new, and, or, xor, not - for later) and
> optionally an queryList(again, later).
> 
> This test is a step towards that goal.  Any advice on how to optimize for
> speed would be greatly appreciated (including rewriting using a whole
> different approach).

Adam,

I'm afraid I only skimmed the script.  A few thoughts: 

 o Union is pretty expensive.  
 o The spatial filter you end up with is going to be pretty complex I 
    think, so it will be quite expensive to evaluate whether things 
    intersect it.  I would suggest just setting an MBR rectangle for the
    spatial filter.  When you do your later Intersect() you can discard
    NULL results. 
 o In general speed is not GEOS's forte, and your could end up asking
    it to evaluate some pretty hard operations. 

> But first, one comment about pymod.ogr.Geometry.Empty().
> When I try:
> selectPoly.Empty()
> I get:
> TypeError: Empty() takes exactly 2 arguments (1 given)
> If I change ogr.py from:
>     def Empty( self, other_geom ):
>         return _gdal.OGR_G_Empty( self._o, other_geom._o )
> to:
>     def Empty( self ): #   , other_geom ):
>         return _gdal.OGR_G_Empty( self._o ) #   , other_geom._o )
> It seems to work.

Indeed, this was a bug in ogr.py.  I have applied the change in CVS. 

Best regards,
-- 
---------------------------------------+--------------------------------------
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