[gdal-dev] Open source vector geoprocessing libraries?

[Ari Jolma]

Jan Hartmann wrote:
>
> On 13-1-2010 15:49, Ari Jolma wrote:
>> Jan Hartmann wrote:
>>>
>>>
>>> Just curious, would it make sense / be possible to implement 
>>> indexing in OGR, something like a
>>> generalized version of Mapserver's shptree, the "quadtree-based 
>>> spatial index for a shapefiles"?
>>>
>>> http://mapserver.org/utilities/shptree.html
>>
>> It could make sense to have a in-memory index for in-memory 
>> geometries. Pehaps use GiST library(1) (I don't know whether it can 
>> use in-memory indexes) for geometries in an OGRGeometryCollection  or 
>> OGRMemLayer if it's available.
>>
>> For other formats it might not make sense because OGR is not 
>> responsible for the actual geometries. As have been said, one should 
>> use PostGIS format, which has this functionality built-in, for larger 
>> and more static datasets.
>>
> Is that so? Reading the OGR API tutorial 
> (http://www.gdal.org/ogr/ogr_apitut.html), I see that all geometries, 
> frowm whatever input source, are represented internally as a generic 
> OGRGeometry pointer, which is a virtual base class for all real 
> geometry classes (http://www.gdal.org/ogr/classOGRGeometry.html). Most 
> of the GEOS functionality can be implemented on OGRGeometries, so in 
> principle the same could be done with indexing libraries (GIST, 
> b-tree, quadtree, etc). Such indices should be written out to disk to 
> be of any use at all, of course, like shptree does.
>

What I meant is that with other formats than the in-memory format, the 
features are stored on disk (possibly even on remote servers) and only 
available for indexing when retrieved. When they are retrieved, they are 
of course OGR objects and accessable through the generic OGR API. Maybe 
it's possible but it would probably mean that the library would need to 
retrieve and go through all the features, and prepare and store into 
some local(?) file the index. Thus I think that for those formats, it's 
up to the format itself to provide the indexing or not.

Ari