| MAP_SET and Polar Stereographic Projections [message #4784] |
Wed, 26 July 1995 00:00 |
Peter Hollemans
Messages: 2
Registered: July 1995
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Junior Member |
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PROBLEM: We have a set of data that was sampled on a polar
stereographic grid, along with two 2-dimensional arrays
of the latitudes and longitudes for the sampling points.
To make a contour plot of the data, we use MAP_SET followed
by CONTOUR. For MAP_SET, we use the /STEREO keyword,
and specify (90, 0) as the center of the projection. We
also use LIMITS to specify the extents of the data. The
resulting plot is a "pie-slice" of the globe rather than
a clipped-down version of just the data region. If we
assume that the data region is square as projected onto
the sterographic plot (ie. it follows the horizontal and
vertical directions of the plotting device) then how could
we plot just the area of interest?
POSSBILE
SOLUTIONS: i) Use some sort of image-clipping routine after plotting
the data to the screen, but this would be device and
resolution dependant. As well, how can we find the
edges of our data?
ii) Plot the data to another projection (ie: cylindrical)
and doctor the boundaries of the data to be square.
We don't really want to lose or gain data that way,
but we _do_ want a square plot because it's easier
to look at and compare to other plots.
iii) Use CONTOUR with the data and draw in the continental
boundaries using the "supmap.dat" XDR data file. We
can be assured of a rectangular region this way.
We're investigating this route, but we're concerned
about RSI changing the format of "supmap.dat" in the
future.
iv) Get RSI to change the LIMITS option so that it
takes a complete polygon instead of assuming a
LAT-LON square.
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