[Gnuplot-info] Spherical geometry diagrams - is gnuplot the right tool?

[<Geo...@bl...>]

Working on drawings for a series of articles on map projections and
wondering if gnuplot is the right tool for this.  Attached are a couple of
samples of the kind of output I'm looking for.
These samples were produced in xfig, with a lot of manual intervention.  Am
looking for an easier and more accurate way to do this process.

If anyone can indicate a way to reproduce these things in gnuplot, I would
appreciate some examples or at least some pointers!

If gnuplot is not the appropriate tool, would appreciate suggestions of
other tools.  I have been looking at G. Nobre's Featpost extension to the
Metapost language (matagalatlante.org/nobre/featpost/doc/featpost-1.html )

1) A sphere tangent to a plane at its south pole.  Meridians drawn with
hidden line removal.  Two lines, drawn in a different style, between the
north pole and the plene, passing through the sphere without
hidden-line removal.

(See attached file: stereog.png)

2) The upper, "north" half of a sphere, with the angle between two
parallels indicated with an arrow and labeled, and the angle between two
meridians indicated with an arrow and labeled.



 (See attached file: latlondome2.png)


3) Upper half of a sphere, an oblique tangent plane to the sphere (hiding
part of the sphere), and a cartesian coordinate system sketched and labeled
on the plane

(See attached file: dome_with_tangent2.png)

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George Heine, PhD
Mathematical Analyst
National IRM Center
U.S. Bureau of Land Management
voice   (303) 236-0099
fax       (303) 236-1974
cell      (303) 905-5382
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