[gdal-dev] compiling GDAL with GEOS on Windows

[Christopher Barker]

Yilmaz Arslanoglu wrote:
> I was considering too
> to utilize
> the Natural Neighbours concept, not only for nearest neighbour
> identification, but also for
> interpolating the values attributed to spatial points.

If you google for "triangulation" and "Delaunay" you'll find lots of 
references and code.

One good one to take a look at is Jonathan Shewchuk's "triangle"

http://www.cs.cmu.edu/~quake/triangle.html

It is fast, robust, and pretty easy to use -- it is a command line 
program, and can also be compiled as a library. I think it will do 
linear interpolation of values to new points for you.

It may have licensing issues -- it one of those annoying "free for 
academic use" clauses, but no standard open source license.

You also may want to take a look at ucar's ntagrid:

http://ngwww.ucar.edu/ngmath/natgrid/intro.html

> since one needs to adapt the tesellation with the newly inserted query
> point at eachnew query.

I don't think Triangle has an API for that, but it does dynamically add 
points itself when you ask it to create a "quality" triangulation, so 
you may be able to hook into that.

As I think about it, though, I'm not sure you need to do that. If you 
are linearly interpolation among your known points (that is, fitting a 
plane to the thre points of the traingle that your new point is in), you 
don't need to include an added point when doing the next one -- yes it 
might be a natural neighbor of a future point, but it will lie on teh 
same plane, so it won't change the result. If you do a fancier 
interpolation, it may make a difference.

As it happens, I need to do something very similar soon, so I'd love to 
hear what you come up with.

-Chris




-- 
Christopher Barker, Ph.D.
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