[OSRS-PROJ] Orthographic Projections and MapServer

Norman Vine nhv at cape.com
Fri Aug 22 15:15:09 EDT 2003

Gerald I. Evenden writes:
> 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.

HeHe a good one, but luckily one with a reasonably simple solution.

For case (2) above you aren't trying to draw the polgon representing 
the Antartic continent. You are drawing the polygon that is obtained by 
subtracting the polygon that represents the Antartic continent from a sphere.
Once one has derived this polygon it is a straight forward operation again


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