> Thanks Bill and Ken,
>
> I had scoured the c.l.i-p archives but never used "regridding" keyword
> which, in hindsight, seems the perfect keyword. The perils of keyword
> searches...
>
> The discussion on INTERPOLATE that you reference (see
http://tinyurl.com/38mr7k)
> is the first time I have ever "gotten" INTERPOLATE. Thank you! The
> function has always felt so awkward because the units x and y are in
> dimensions - it always left me feeling a little disconnected from the
> physical meaning. I'll get over it.
>
> For my purposes the INTERPOLATE method is probably just the ticket,
> but I do have this lingering question about the fact that the input
> values are drawn from the surface of a sphere. What are the
> conditions under which I do need to worry about it? Is it the spacing
> between the input values? The extend over the sphere? Some
> combination?
Remember, interpolation is an approximation. You make assumptions about
the
behavior of a function between known (tabulated) points. Bilinear
interpolation is the crudest possible interpolation scheme.
Doing bilinear interpolation on a sphere is also an approximation, as
the bilinear interpolator is strictly defined in Cartesian coordinates.
If I remember correctly, though, your grid is rather finely spaced. On
that scale it is probably a very good approximation to assume that the
world is flat. If you are worried about errors at that level, or you have
a
better idea of the actual shape of your function, then you could use a
higher-order
interpolator. That would depend on your purpose. It is a good idea to
think about these things, but then I'm not doing geodesy. :-)
Ken
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