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Re: [ferret_users] Plotting Satellite Wind Vectors
Thanks Ned for bringing this up. I am guessing that in Steve's plot the
main problem is that the vectors are all in a fairly small region but
the vectors are scaled too large to be able to see anything.
Note that in addition to mp_poly_vectors.jnl there is a script
poly_vectors.jnl for the case where we are not working with a map
projection. The poly_vectors_demo script shows both cases.
E. D. Cokelet (Ned) wrote:
Dear Steve,
I was never happy with the way plot_vectors.jnl worked, but it should
not be as bad as what your graphic shows. However on map projections
it is just plain wrong. Try it near the poles on a polar projection
and you'll see. So I wrote the mp_poly_vectors.jnl script a couple of
years ago. Ansley generalized it a bit, and it's available as a public
Ferret script. Run the poly_vec_demo.jnl script to see it in action.
Use mp_poly_vectors.jnl for map-projected vectors.
P.S. I would caution you though, that there are still some problems.
The way most of the Ferret mp_xxx commands (e.g. mp_line.jnl) are
written, they redefine the mapping between (lat,lon) values in one's
present data set, and the x_page, y_page parameters that define the
mapping from (lat,lon) to the page for each and every new data set you
plot. That's not desirable. If you draw a large map of coastlines,
say, over a large region and then want to add data to it that are
defined by its axes in a much smaller region, the mapping is redefined
through Ferret's delayed evaluation philosophy. That's not correct.
What you really want is to set up that mapping once and for all for
your entire plot, say when you plot the coastline, and then leave it
unchanged when you add other things like labels, graticules, vectors,
etc. I get around this by defining my own mp_line.jnl, etc. scripts
that have the
let/quiet mp_central_meridian = `mp_central_meridian`
let/quiet mp_standard_parallel = `mp_standard_parallel`
lines commented out. So what you want is mp_central_meridian and
mp_standard_parallel defined once for the projection you desire, and
never redefined by some other mp_xxx command.
------------------------------------------------------------------------------------------
Edward D. (Ned) Cokelet, Ph.D. Edward.D.Cokelet@noaa.gov
Oceanographer
NOAA/PMEL off: (206) 526-6820
7600 Sand Point Way NE fax: (206) 526-6485
Seattle, WA 98115-6439
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