[Qgis-user] concave hull/alpha shapes in QGIS

[Alex Mandel]

On 01/02/2012 07:36 PM, maning sambale wrote:
> We have a nifty convex hull in ftools/vector plugin. I'm looking for
> ways to create concave hulls.  I have a set of csv points as a source
> to generate the polygon.  This is updated regularly by non-geo field
> workers.  Any workaround to generate concave hull in QGIS?
> 
> Mappy new year to all!
> 
> PS. I've seen old discussions in the qgis-dev list.

They can be done in R, and therefore done using ManageR QGIS plugin.
The R package is alphahull

Though you might want to look at other methods depending on what your
actual goal. I messed around with them in regards to territories from
GPS telemetry and I believe Anne Ghisla has a whole thesis on the topic.

In the end a professor of mine came up with using a density function as
the fastest method to get good results.

I can find the R code if it will help you.

Thanks,
Alex