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Re: [ferret_users] Plotting curvilinear vectors
Hello Ned,
Thank you for your response. I had a go with "poly_vector.jnl", but
there is something wrong with the plot. My winds are not on a regular
grid, but rather scattered, such as satellite data. I tried this:
file/var="lat,lon,u,v" fort.8 !a listing of lat,lon,u,v
go basemap x=280:310 y=20:40 5
go poly_vectors lon lat u v 10 "arrow" !randomly chose 10 for scale
polygon/overlay/noax/nolab/line plt_x_arrow,plt_y_arrow !no fill, just
vectors
This appears:
*** NOTE: Ambiguous axes in 2D coordinate arrays
*** NOTE: Continuing as /COORD_AX=Y
I tried making a 2-d array of lat,lon,u,v, but I still get this message
and the plot is still not right. Any suggestions? I am able to get
the right plot with "plot_vectors.jnl" from Patrick Brockman, but don't
know how to implement the key.
Thanks,
Steve
Quoting "E. D. (Ned) Cokelet" <Edward.D.Cokelet@noaa.gov>:
I think that the Ferret vectors are wrong because they were written
with the idea that the entire vector - tail location, shaft length,
arrow head and direction - should be transformed in your coordinate
transformation. That is invalid. The only thing the should be
mapped is the tail locations. The shaft length and arrowhead should
not be transformed. That leaves the direction which is a bit
trickier. I wrote a journal script that Ansley has made available to
the community called poly_vector.jnl. It works with the various
Ferret map projections, e.g. Mercator, etc, gets the directions right
and lets you scale the vector lengths. If you can use one of those
for your curvilinear mapping, or make up a new mapping transform that
follows their style, then you should be able to map vectors
correctly with the new script. Billy Kessler has modified this a
bit to give better arrowheads when the arrows get really short. I
am not sure if that is implemented community-wide yet.
------------------------------------------------------------------------
------------------
Edward D. (Ned) Cokelet, Ph.D. Oceanographer
NOAA/PMEL off: (206) 526-6820
7600 Sand Point Way NE fax: (206) 526-6485
Seattle, WA 98115-6439
Edward.D.Cokelet@noaa.gov
The contents of this message are mine personally and do not
necessarily reflect any position of the Government or the National
Oceanic and Atmospheric Administration.
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