[Gdal-dev] Using OGR Python to analyse stream layers

[Chris G. Nicholas]

folks might want to look at the new GEOS functionality in PostGIS, that includes buffering, intersect, union, etc.

seems to work beautifully...

Chris Nicholas
GlobeXplorer

-----Original Message-----
From:	Frank Warmerdam [mailto:warmerdam at pobox.com]
Sent:	Mon 2/9/2004 10:03 AM
To:	gdal-dev at remotesensing.org
Cc:	
Subject:	Re: [Gdal-dev] Using OGR Python to analyse stream layers
Christopher Fonnesbeck wrote:
> Thanks for the advice! What if I had a polygon coverage with affected 
> polygons instead; could those then be intersected with a stream 
> coverage, or is that outside of OGR's realm?

Chris,

OGR does not support much in the way of geometry intersection operations.
What it does offer is a bounding box spatial filtering.  That is, a
rectangular bounding box can be set as a spatial filter, and then when
you iterate through the features, only those intersecting that bounding
box will be returned.

For the time being I have tried to leave complex geometry operations to
packages like GEOS though I do hope to incorporate their use into
OGR at some point.

> Is there documentation/examples of how OGR handles line features like 
> stream networks?

There is substantial documentation on the C/C++ interface to OGR ... less
on the python interface. I can provide a small sample script that would
read lines from a data source, and print out the set of vertices if you
need it.

> I presently use MySQL for all my GIS databasing, and version 4 now 
> supports storage of spatial features. Is there a mysql driver for OGR?

I am not all that familar with the new spatial features in MySQL.  I am
not convinced it includes rigerous geometry operations though.  There is
not any direct support for the new MySQL geometry types in OGR though I hope
to incorporate that at some point, possibly layered on the existing ODBC
driver in OGR which I have been using for MySQL based applications so far.

I'm sorry I don't have a more cut-and-dried solution for you.

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

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