| Limit on Polar Stereographic Projection? [message #10640] |
Fri, 26 December 1997 00:00 |
lin
Messages: 1
Registered: December 1997
|
Junior Member |
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Hi IDL users,
Can a polar stereographic map projection allow a specification
of map boundary? Our research group needs to generate a series of
polar stereographic maps of a subset of the southern hemisphere
between some specified latitude (-30 degrees, see the example below)
and the south pole. However, when we use /limit keyword (either
four elements for the two opposite diagonals or eight elements for
the left, top, right, bottom regions) in the map_set call to specify
mapping boundaries, we get undesirable plots:
Our Sun workstation idl cuts out an entire quadrant from the
map, viz the quadrant from longitude -180 to -90 as a coding
example appended below.
Our Linux idl does not cut out the quadrant, but makes an ugly
plot that extends outside the limiting -30 degree latitude circle
out along the plot window's diagonals.
Everything is ok with the default of 0 degree latitude limit.
(I.e. leaving off the "limit=" keyword.) But if that keyword
is included with the 8 element vector specifying the latitudes
and longitudes of the desired boundary, then the above problem
occurs.
We don't want to limit ourselves to a 90 degree range of
latitude for the polar stereographic type of plot, so we need to
find a way to make idl plot the entire longitude range of -180
to +180 for any arbitrary latitude limit (for either the north
or south pole projection).
Does anyone know what causes the problem and how to fix it?
Thanks in advance for your help.
Jin
___________________________ example ------------------------------
--------------------------- begin cut ----------------------------
; This is an idl test program to draw the polar
; stereographic map projection with an explicit
; latitude limit, with the projection plane tangent
; to a pole (the south pole in this example).
;
;
; Define lat,lon at left, top, right, bottom edge of plot window
;
lat_lon_limits=[-30.,-90., -30.,0., -30.,90., -30.,180.]
;
;
; Define center of projection (tangent point in lat,lon space)
;
p0lat = -90.
p0lon = 0.
;
;
; Define rotation angle
;
rot = 0.
;
;
; Set the map transformation, and plot the continents plus lon,lat lines
;
map_set, p0lat, p0lon, rot, $
/stereographic, $
/grid, $
/continent, $
/isotropic, $
/noborder, $
/label, $
latdel=10, $
londel=45, $
limit=lat_lon_limits
;
;
; Terminate normally
;
end
--------------------------- end cut ----------------------------
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