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I have a shapefile with around 19,000 points. Its basically export from a raster. No i need to extract polygons, by aggregating the points which have same value.The field who's value i am going to use for aggregation is dynamically calculated each time using the elevation of points. NOw i need to spit out polygons. How can I do that using GDAL? is there a utility to do it. Any other opensource solutions are welcome. I have ArcGIS which has a toolbox called 'Aggregate Points' but somehow licence for it is missing.

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It sounds like you would like a convex hull, which is just a way of wrapping a border around like points. See the OGR reference.

Alternately, use the Minimum Bounding Geometry tool in the data management toolbox, which requires an ArcInfo license.

If you later need the polygons to cover then entire area, you can calculate Thiessen polygons from them.

Finally, this is also possible in R using the AlphaHull package.

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I tried the Minimum Bounding Geometry Tool before, but in that too the convex hull is disabled. When i checked the error code this is what i get : "Only RECTANGLE_BY_AREA and RECTANGLE_BY_WIDTH geometry types are available at an ArcView or ArcEditor license; all other geometry types require an ArcInfo license. See tool reference for more details. " Any clues if this is an configuration issue and can be resolved? – Shaunak Aug 17 '11 at 0:21
Sorry - I didn't realize that tool wouldn't work without ArcInfo. I imagine it could be resolved if you have an ArcInfo license. Do you have one? I've never configured ArcGIS licenses, so someone else may have to help with that. – Patrick Aug 17 '11 at 0:29
On another note, it'd be nice if you improved your acceptance rate by accepting an answer here and on your previous questions. – Patrick Aug 17 '11 at 0:30
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Sorry, I am not frequent on this flavor of stack exchange, but my stack overflow profile is pretty good :) infact i did accept some answers that i should have. I need to check with our sys admin about the arcInfo Licence. – Shaunak Aug 17 '11 at 0:58

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