| map_set and limit question [message #56283] |
Fri, 12 October 2007 11:28 |
wgallery
Messages: 32
Registered: December 1998
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I am plotting some satellite data with a Stereographic projection. To
create a projection centered on the N Pole and extending from 30 deg N
to 90 deg N, I use:
map_set,/stereographic, 90.0, 0.0, limit = [30, -90, 30.0, 180., 30.0,
90.0, 30, 0],/isotropic
Now I want to center and zoom in on a feature in the image: i.e., I
want to change the projection so that it is centered on a feature
centered at lon=clon, lat=clat and extending 45 deg in 'latitude' from
the center. The question is: how do I construct the keyword limit for
this situation?
My approach is to perform a coordinate transformation to move the
center of the feature to the N Pole and perform the inverse of this
transformation on the value of limit= [45, -90, 45.0, 180., 45.0,
90.0, 45, 0] to get the new value of limit to use in:
map_set,/stereographic, cat, clon, limit = new_limit,/isotropic
The coordinate transformation would consist of a rotation about the Z
axis by -clon followed by a rotation about the Y axis by 90-clat.
This puts the point [clat, clon] at the N Pole.
However, the details of the coordinate transformation escape me. I
know it is a simple matrix multiplication but am stumped on the
values.
Does anyone know offhand the equations for the coordinate
transformation, or have a better approach to the problem?
Cheers
Bill Gallery
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