| Experience with TRIGRID? [message #1393] |
Fri, 08 October 1993 06:44 |
manizade
Messages: 9
Registered: October 1993
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Junior Member |
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I have tried using the TRIGRID procedure on a Sun using both IDL
3.0 and 3.1 with disappointing results. The simple example in
the IDL Basics book worked fine; when I used my own data the
"interpolation" produced odd values in the output (e.g. spikes),
particularly at the boundaries of the triangular regions. The
problem is worse when the number of points in the interpolation
grid is increased.
For example I called trigrid three ways and looked at the min
and max of the output:
triangulate,xvec,yvec,tr,boundary,repeats=reps
t=trigrid(xvec,yvec,zvec,tr,/smooth)
tt =trigrid(xvec,yvec,zvec,tr)
ttt=trigrid(xvec,yvec,zvec,tr,grid_spc,grid_win); <--{ 250x250grid
raw data yvec min & max : 0.0560000 0.598000
smth grid t min & max : -0.112013 0.760076
lin grid tt min & max : -1.00000 0.652344
large grid ttt min & max : -2.82153 1.00781
Obviously a linear interpolation should not produce values
outside of the input value range.
I have since written a program to sidestep trigrid by using
triangulate and polyshade, which produces a 2-D image I can
manipulate. But I would rather work with the interpolated 3-D
data that trigrid is supposed to produce.
Can anyone please provide some insight into what TRIGRID is
doing? Has anyone encountered bugs? Are there restrictions that
are not documented in the IDL Help?
Thanks in advance for any ideas.
--
Mr. Serdar S. Manizade <manizade@aol3.wff.nasa.gov>
Airborne Oceanographic Lidar Project
NASA/GSFC/Wallops Flight Facility, Wallops Island, VA
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