[OSRS-PROJ] Projection problems at horizon

[Bart Adriaanse]

Dear proj users,

I am experiencing a problem at the horizon while doing worldmap
projections.

For example, i take worldwide coastline data in Lat-Lon and i project
them using orthographic projection to create a view of the globe similar
to what one would see from space.

Instead of ending up with a graphic like the one in the proj
documentation, i end up with several lines that run from the horizon to
the center of the map.

No doubt what is happening is that if a coordinate is beyond the
horizon, it will be returned as zero by the projection formulae,
indicating that it is not visible. What i was hoping for is that these
coordinates would be "snapped" to the nearest visible point on the
horizon instead of the projection origin, thus avoiding these undesired
lines from the horizon to the center.

No need to say, the ortho projection is not the only one with this
behaviour and the results are even worse when i project a bunch of
country polygons...

I would imagine that i am not the first one trying to adress this
problem and would greatly appreciate suggestions/comments form other
proj.4 users.

Best Regards,

Bart Adriaanse
Demis bv
www.demis.nl
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