[gdal-dev] Calculate footprints of shapefiles

[Armin Burger]

Marius,

  thanks for the suggestion. I don't know if shapely supports 
re-projection of geometries or has a simplify algorithm, which I will 
both need. There could be some other functions of GDAL/OGR that I might 
need in the future as well. So in principal I'd prefer to stick to GDAL.

armin

On 16/03/2011 01:35, Marius Jigmond wrote:
> Armin,
>
> Not sure if this would be straightforward in GDAL but you might want to
> consider a combination of GDAL + Shapely
> (http://gispython.org/shapely/docs/1.2/manual.html#cascading-unions).
> What you're trying to do is spatial analysis not directly implemented in
> GDAL. Shapely requires that you're working with Cartesian coordinates.
> The upside is that it has WKT/WKB support for direct loading into
> PostGIS.
>
> -marius
>
> On Wed, 2011-03-16 at 01:08 +0100, Armin Burger wrote:
>> Hi all
>>
>> I would like to catalogue shapefiles scattered over lots of directories
>> of the file system and store retrievable information of the shapefiles
>> in a PostGIS layer. Extracting parameters like extent, projection,
>> fields, etc works very fine with GDAL's Python bindings.
>>
>> But I would also like to store a sort of "footprint" of the whole
>> shapefile as a geometry object since the extent is a bit coarse
>> geographic representation of the shapefile.
>>
>> So far I have no better idea than eg. for polygon shapefiles looping
>> through all features, applying a Union function on them. And at the end
>> trying to use the Simplify method on the resulting polygon that will be
>> used as the footprint.
>>
>> This is for sure not very efficient for larger shapefiles with lots of
>> records. And for line and point shapefiles I still don't have a clue how
>> their records could be represented by an enclosing polygon (maybe the
>> Boundary functions does something like this...).
>>
>> Any ideas how this footprint generation could be achieved in a feasible
>> way using GDAL/OGR Python?
>>
>> Cheers, Armin
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>
>