[GRASS-user] Re: r.surf.nnbathy interpolation to whole region

[Maciej Sieczka]

Luigi Ponti wrote:
> Maciej Sieczka wrote:
>> Luigi Ponti wrote:

>>> (in principle this seems possible: outer Voronoi cells just get
>>> bigger)?

>> I don't exactly understand what you mean. Could you elaborate
>> please?

> What I meant is that the outer Voronoi cells may extend up to the 
> region's bounding box, with consequent new Voronoi cells for 
> interpolation points outside the convex hull, please see 
> http://quartese.googlepages.com/voronoi

nnbathy performs Delaunay triangulation, not Voronoi tesselation. I
(darkly) understand there is a mathematical relation between the two,
but I don't see how it could apply in your example. If this is just my
ignorance please explain more.

Anyway - what could be done to overcome the trimming to convex hull
effect: you need to make sure that the convex hull for your input cells
covers your whole area of interest - ie. enlarge region enough for
important input cells not to be omitted. If cells in the input raster
are distributed so that a convex hull covering the whole area of
interest is not possible, you need to enhance your input raster.

r.to.vect -z feature=point followed by v.hull might be faster for
testing than trial and error with r.surf.nnabthy itself.

Cheers,
Maciek