[geos-devel] concave hull

[Mike Toews]

On 10 March 2014 00:36, Riccardo Cohen <r.cohen at realty-property.com> wrote:
> I need to generate a concave hull for a collection of points. I found only
> convexHull() in Geos 3.5.0.
> But it seems that PostGis uses some GEOS functions to make a concave hull :
>
> http://postgis.net/docs/ST_ConcaveHull.html
>
> Is it possible simply in a C program without having to implement a special
> new algorithm ?
>
> Thanks a lot

No C library function is available for ConcaveHull. The algorithm is
implemented in PL/pgSQL:
http://trac.osgeo.org/postgis/browser/trunk/postgis/postgis.sql.in#L5098

The code could probably be adapted to a somewhat lengthy C routine,
which would call several GEOS functions. However, some of the
underlying functions found in the algorithm are not available through
GEOS, such as:
 * ST_Translate, since there are oddly no affine transformation
   abilities with GEOS
 * ST_ForceSFS, which is part of liblwgeom

-Mike