[OSGeo-Discuss] open source polygon cluster aggregation algorithm?

[G. Allegri]

I'm looking for an algorithm to do polygon cluster aggregation,
similar to the ArcInfo "Aggregate Polygon" [1].
I know about GEOS "Cascaded Union", but I need two more features:

1 - clustering of polygons that fall within a a certain threshold
distance from each other
2 - mantain orthogonality, i.e. the original angles/shapes

Both can be achieved with the ArcInfo tool...

thanks a lot,
Giovanni

[1] http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=aggregate_polygons_%28data_management%29