[Proj] Some questions

[support.mn at elisanet.fi]

Ok,

I understand the problems very well. The ultimate solution would be such
a definition, that would allow one to define any complexity there is possible
and still have some easy default solutions also.

Janne. / MNS Support

-----------------------------------

Noel Zinn [ndzinn at comcast.net] kirjoitti: 
> Janne,
> 
> Your two objectives, (1) full ellipsoid control and (2) more and more
> accuracy, are contradictory and self defeating.  As we learned in the Google
> Maps debate, allowing full ellipsoid control changes the definition of the
> projection that (you think) you are using.  For example, the spherical
> Mercator is conformal if the geographicals (lat/lon) come from a sphere of
> the correct radius.  But if we feed the spherical Mercator equations
> geographicals that come from an ellipsoid, the result is non conformal.  The
> projection we are actually using is not the spherical Mercator but some
> Pseudo Mercator because the equations for distortion (scale factor in this
> case) have to be rewritten.  That is not "more and more accuracy".  It's the
> opposite.  Who knows what happens to other conformal projections?  Who knows
> what happens to the equal area property of equal area projections?
> Cartography is more than XY to and from LL.  Projections have properties.
> Full ellipsoid control destroys those properties.
> 
> Noel Zinn
> 
> 
> -----Original Message-----
> From: proj-bounces at lists.maptools.org
> [mailto:proj-bounces at lists.maptools.org] On Behalf Of support.mn at elisanet.fi
> Sent: Saturday, April 04, 2009 8:51 AM
> To: PROJ.4 and general Projections Discussions
> Subject: Re: [Proj] Some questions
> 
> I understand. The problem for our part is that we are seeking
> all the time more and more accuracy. Could we put it behind
> some switch? The standard version would not allow such
> parameters, but if one switched some switch on, then one
> could use such parameters.
> 
> Something like:
> 
> #define ALLOW_FULL_ELLPS_CONTROL
> 
> The full control of the calculation is important for us since we have
> to get accurate results (especially in the future). If it is behind some
> switch, that does not bother us? The other people will also not
> see any difference, since the switch could be off by default.
> 
> Regards: Janne. / MNS Support
> 
> ----------------------------------------
> 
> > > For example something like:
> > > 
> > > pellps=.....
> > > dellps=.....
> > > 
> > > where "pellps" would stand for "projection ellipsoid" and
> > > "dellps" for "datum ellipsoid".
> > > 
> > > and when both are the same, just normal
> > > 
> > > ellps=....
> > > 
> > > where "ellps" stands for both datum and projection. That
> > > would not alter the existing definitions, but allow more
> > > accurate control of the ellipsoids involved.
> 
> > 
> > No, no such capability has been implemented.  I'm still not too keen
> > on doing so either for reasons previously stated.
> > 
> 
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