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Re: [ferret_users] Creating and using an irregular mask, as in the recent question regarding filling data over China
Hi all,
While we're on the topic, I have one more thing to throw out there. Some
time back when this question came up we did a little investigation and
wrote an external function based on the code by W. Randolph Franklin,
found in his web pages at
http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
It does the same kind of computation as what Mick is doing in his Ferret
script, InsidePolygon.jnl. We have not had a chance to really test it.
Mick's method of getting the polygon outline with his polydef_close.jnl
script is a big step towards being able to do useful things with either
this function or the InsidePolygon.jnl script. The only advantage of
using the Ferret external function is that it should be faster.
I've put a tar file with an external function at this location
ftp://ftp.pmel.noaa.gov/ferret/special_request/ansley/pt_in_poly.tar.gz
It contains this new function.
yes? show func pt_in_poly
PT_IN_POLY(A,XVERT,YVERT)
Return -1 outside, 0 if on edge, 1 if inside polygon
A: Variable on the XY grid and region to be tested
XVERT: X-coordinates of vertices of polygon
YVERT: Y-coordinates of vertices of polygon
To use the pre-compiled external function, put the appropriate
pt_in_poly.so file in the directory that is pointed to by the
environment variable FER_EXTERNAL_FUNCTIONS.
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