<br><font size=2 face="sans-serif">Noel, thank you for sharing the explanation.
Mike Finn</font>
<br>
<br>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">From:</font>
<td><font size=1 face="sans-serif">"Noel Zinn" <ndzinn@comcast.net></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">To:</font>
<td><font size=1 face="sans-serif">"'PROJ.4 and general Projections
Discussions'" <proj@lists.maptools.org></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Date:</font>
<td><font size=1 face="sans-serif">04/07/2009 06:03 AM</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Subject:</font>
<td><font size=1 face="sans-serif">Re: [Proj] Some questions</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Sent by:</font>
<td><font size=1 face="sans-serif">proj-bounces@lists.maptools.org</font></table>
<br>
<hr noshade>
<br>
<br>
<br><tt><font size=2>Janne,<br>
<br>
Your two objectives, (1) full ellipsoid control and (2) more and more<br>
accuracy, are contradictory and self defeating. As we learned in
the Google<br>
Maps debate, allowing full ellipsoid control changes the definition of
the<br>
projection that (you think) you are using. For example, the spherical<br>
Mercator is conformal if the geographicals (lat/lon) come from a sphere
of<br>
the correct radius. But if we feed the spherical Mercator equations<br>
geographicals that come from an ellipsoid, the result is non conformal.
The<br>
projection we are actually using is not the spherical Mercator but some<br>
Pseudo Mercator because the equations for distortion (scale factor in this<br>
case) have to be rewritten. That is not "more and more accuracy".
It's the<br>
opposite. Who knows what happens to other conformal projections?
Who knows<br>
what happens to the equal area property of equal area projections?<br>
Cartography is more than XY to and from LL. Projections have properties.<br>
Full ellipsoid control destroys those properties.<br>
<br>
Noel Zinn<br>
<br>
<br>
-----Original Message-----<br>
From: proj-bounces@lists.maptools.org<br>
[</font></tt><a href="mailto:proj-bounces@lists.maptools.org"><tt><font size=2>mailto:proj-bounces@lists.maptools.org</font></tt></a><tt><font size=2>]
On Behalf Of support.mn@elisanet.fi<br>
Sent: Saturday, April 04, 2009 8:51 AM<br>
To: PROJ.4 and general Projections Discussions<br>
Subject: Re: [Proj] Some questions<br>
<br>
I understand. The problem for our part is that we are seeking<br>
all the time more and more accuracy. Could we put it behind<br>
some switch? The standard version would not allow such<br>
parameters, but if one switched some switch on, then one<br>
could use such parameters.<br>
<br>
Something like:<br>
<br>
#define ALLOW_FULL_ELLPS_CONTROL<br>
<br>
The full control of the calculation is important for us since we have<br>
to get accurate results (especially in the future). If it is behind some<br>
switch, that does not bother us? The other people will also not<br>
see any difference, since the switch could be off by default.<br>
<br>
Regards: Janne. / MNS Support<br>
<br>
----------------------------------------<br>
<br>
> > For example something like:<br>
> > <br>
> > pellps=.....<br>
> > dellps=.....<br>
> > <br>
> > where "pellps" would stand for "projection ellipsoid"
and<br>
> > "dellps" for "datum ellipsoid".<br>
> > <br>
> > and when both are the same, just normal<br>
> > <br>
> > ellps=....<br>
> > <br>
> > where "ellps" stands for both datum and projection.
That<br>
> > would not alter the existing definitions, but allow more<br>
> > accurate control of the ellipsoids involved.<br>
<br>
> <br>
> No, no such capability has been implemented. I'm still not too
keen<br>
> on doing so either for reasons previously stated.<br>
> <br>
<br>
_______________________________________________<br>
Proj mailing list<br>
Proj@lists.maptools.org<br>
</font></tt><a href=http://lists.maptools.org/mailman/listinfo/proj><tt><font size=2>http://lists.maptools.org/mailman/listinfo/proj</font></tt></a><tt><font size=2><br>
<br>
_______________________________________________<br>
Proj mailing list<br>
Proj@lists.maptools.org<br>
</font></tt><a href=http://lists.maptools.org/mailman/listinfo/proj><tt><font size=2>http://lists.maptools.org/mailman/listinfo/proj</font></tt></a><tt><font size=2><br>
</font></tt>
<br>
<br>