[OSRS-PROJ] Orthographic Projections and MapServer

Gerald I. Evenden gerald.evenden at verizon.net
Thu Aug 21 19:52:15 EDT 2003

The more I think about it, the more I think there may be a moderately
easy solution to limb clipping.  The stickiest problem I see at the
moment is how to determine what the condition is when all the points
defining the area to be filled are invisible.

Imagine this problem:

An orthographic view of the North Pole.  A set of data for the
Antarctic continent is given but all the points are invisible.

1. If the Antarctic continent area was to be filled then no
	fill operation is made.

2. If everything BUT the Antarctic continent is to be filled
	then everything inside the circular limb is filled.

Hmmm.  I think the solution to this problem again boils down to
the left-/right-handedness of the fill area to the vector sequence.

An additional note, I think previous notes about variations with
different projection will create different clipping problems is
correct and a table of methods will have to be established for
a graphic program.  I have done this manually in using my
ad hoc graphic procedure for PROJ.4 illustrations.
Time to dig out the dusty old graphics books and study the fill
problem.  :-(

Gerald I. Evenden <gerald.evenden at verizon.net>

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