[GRASS5] GRASS and lat/long with sphere

[Markus Neteler]

On Tue, Oct 01, 2002 at 10:54:10AM +0100, Glynn Clements wrote:
> 
> Markus Neteler wrote:
> 
> > > while trying to define a lat/long location with Sphere instead
> > > of WGS84, I found in
> > > 
> > > src/libes/gis/ellipse.table
> > > # earth as a sphere:
> > > # There is a bug in libes/gis/get_ellipse.c, where a function
> > > # return e=0.0 in any case. So do not use sphere!
> > > # sphere        "Spherical Earth"               a=6370997.000
> > > 
> > > Is there no/any hope to fix the code (I don't know how...).
> > 
> > [Note that also for Mars planet GIS activities the sphere is
> >  required. So we should really support it]
> > 
> > ... of course I tried it by activating the "sphere" line. What happens:
> > 
> > - select lat/long
> > 
> > Please enter a one line description for location <sphere>
> >  
> > > sphere test
> > =====================================================
> > sphere test
> > =====================================================
> > ok? (y/n) [y]
> > WARNING: Line 144 of ellipsoid table file
> > 
> > </mpa_sw/ssi/BIO/software/GRASS5.0.0/grass5bin_cvs/grass5/etc/ellipse.table>
> > is invalid
> >  
> > Please specify ellipsoid name
> > Enter 'list' for the list of available ellipsoids
> > Hit RETURN to cancel request
> > >
> > 
> > The warning occurs at
> > src/libes/gis/get_ellipse.c
> > line 329
> 
> The function get_a_e2_f() in get_ellipse.c requires that e2 (the
> eccentricity-squared) is greater than zero (otherwise it returns zero,
> indicating an error).
> 
> Changing it to allow e2 to be equal to zero doesn't result in any
> problems which are immediately obvious. However, it may be that some
> code can't cope with this (e.g. computing the reciprocal). In all
> probability, the only way to find out is to make the change and wait
> for bug reports.

May I ask you to apply the change? As far as I understand it should
only users of "sphere" ellipsoid. So it is no severe change (I have
already another tester in mind, hi Alessandro F.!).

Thanks,

 Markus