Re: [OctDev] griddata / delaunay

[Pedro T. <pt...@te...>]

Sorry I missed the thread from the beginning... out for holidays, you know...

> 1.  Griddata is used for (linear) interpolation and, as such, should
> suffer not at all when using delaunay with the QJ option.  Let's
> implement this, please.  It is a very easy fix, as indicated in my patch
> for griddata.m at the beginning of this thread.

I did contact Brad Barber months ago about this. He didn't recomend it. He 
said it would be better to tell qhull to triangulate the output. This is 
implemented in a function not included in octave-forge that I wrote to have 
better control over qhull. I'll attach it. If you pass a third 'true' 
parameter to the function it will triangulate the output. Maybe all the 
convhull,delaunay and voronoi functions should be just wrapper functions to 
this.

>
> 2.  Segfaults should never occur, but I have found an illustrative case
> where it does with delaunay.  I'll leave this to the experts.

But it does since some of the facets are coplanar and qhull tries to return 
n+1 vertices on an n columns matrix. This is solved in my qhull 
implementation by adding columns to the matrix and filling with 0 indexes 
when there's no vertex (in simplicial facets).

If you want to try qhull function, I send it attached. Just compile with like 
any other geometry package function. delaunayn(X) would be replaced by 
qhull(X,"d",true).


Regards,
Pedro