[OSRS-PROJ] orthographic projection with proj4 and mapserver.

Gerald I. Evenden gerald.evenden at verizon.net
Wed Aug 13 22:06:43 EDT 2003

On Wed, 2003-08-13 at 21:24, Tom H wrote:
> > BTW, libproj4 forward routine returns HUGE_VAL when it cannot project a
> > point.  Program [l]proj returns an "*".  The HUGE_VAL method has been
> > in PROJ.4 use for a *long* time so I suspect that the problem lay in
> > the calling software.
> > 
> > 
> If HUGE_VAL was returned against the 0,0 would the image have had shards out
> to infinity rather than to 0,0?

I have no idea where the 0,0 values comes from.  In theory, libproj
procedures should produce HUGE_VAL,HUGE_VAL for invisible or non-
projectable points.  It is up to the calling program to make sense
of this condition---making 0,0 does no make sense.

The only condition that I will address is that libproj is producing
0,0 for invisible points.  So far, no evidence has been given to
demonstrate libproj is producing 0,0.  A quick check with lproj
gives *,*s for invisible points so presumably the library is working.
The illustrations I made many years ago indicated that *,* was
being correctly produced as the graphic routines depended upon
this return for invisible points.

To demonstrate that libproj is in error I need values for the
pj_fwd input and its return values.  A graphic is not considered
evidence of failure because of too many operations external to
libproj library calls that can be in error.

As an unrelated aside, why is an elliptical earth specified for a
global scale illustration?  A lot of unnecessary work for such a
small scale.
Gerald I. Evenden <gerald.evenden at verizon.net>

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