GRIDDATA woes

Hi All,

I have been having a problem similar to this one...
http://tinyurl.com/2spe3v


The solution to the problem in the above posting was to use GRID_INPUT
to filter and reorder the data *before* calling QHULL and GRIDDATA.
That doesn't seem to be the case this time as I faithfully perform
these steps.  However, the error message indicates that it is
something similar is going on.

The big picture is that I have an irregular grid (actually it is
regular in longitude but irregular in latitude) that I want to
interpolate onto a regular grid.  I have assembled a mockup of the
situation in this procedure...
http://www.tidewater.net/~pemaquid/counterclockwise_fail.pro

The error message when the above is run is ...

SeaDAS> z=counterclockwise_fail()
% GRIDDATA: Triangle 5 not in counterclockwise order.
% GRIDDATA: Triangle 6 not in counterclockwise order.
% GRIDDATA: Triangle 7 not in counterclockwise order.
% GRIDDATA: Triangle 17 not in counterclockwise order.
% GRIDDATA: Triangle 30 not in counterclockwise order.
% GRIDDATA: Triangle 31 not in counterclockwise order.
% GRIDDATA: Triangle 34 not in counterclockwise order.
% GRIDDATA: Triangle 40 not in counterclockwise order.
% GRIDDATA: Triangle 42 not in counterclockwise order.
% GRIDDATA: Triangle 49 not in counterclockwise order.

I have tried changing the values in the code to double.  That results
in a similar set of errors but for a different set of triangles.

% GRIDDATA: Triangle 4 not in counterclockwise order.
% GRIDDATA: Triangle 5 not in counterclockwise order.
% GRIDDATA: Triangle 6 not in counterclockwise order.
% GRIDDATA: Triangle 16 not in counterclockwise order.
% GRIDDATA: Triangle 33 not in counterclockwise order.
% GRIDDATA: Triangle 35 not in counterclockwise order.
% GRIDDATA: Triangle 36 not in counterclockwise order.
% GRIDDATA: Triangle 39 not in counterclockwise order.
% GRIDDATA: Triangle 42 not in counterclockwise order.
% GRIDDATA: Triangle 45 not in counterclockwise order.

Bah!

I have seen a number of messages on the newsgroup about interpolation
from an irregular grid to a regular one.  None appear to address the
issues around gridding on a sphere. I don't think I can use anything
as simple as INTERPOLATE since the input array is sampled at irregular
intervals.

So how is this kind of interpolation supposed to be done?

Thanks!
Ben

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