Upgrade Problems - Additional Info

[tim]

Hi Frank,

I appreciate your interest on this, but perhaps taking a closer look at the 
Mercator first would be more fruitful. I got a  number of replies from the 
PROJ4 list that indicate the problem is related to the Mercator 
characteristics, i.e.

From: Clifford J Mugnier <cjmce at lsu.edu>
 >Computing distances is a folly on the Normal Aspect
 >Mercator.  With two endpoints, just compute the inverse of the cartesian
 >coordinates back into latitude and longitude and then compute the correct
 >distance with a geodesic inverse.

From: Paul Ramsey <pramsey at refractions.net>
 >For a Mercator map of all of California, there is no *right* scale
 >bar.  The scale at the top will be different from the scale at the
 >bottom.  This is true of any Mercator map, just actually visible on
 >maps of larger areas.  So the scale bar Mapserver is generating is
 >probably right for *one* part of the map (perhaps the top or bottom?)
 >and the scale bar from your paper map is right for *one* part of the
 >map (the middle, maybe? or maybe for right where it is?).

 >For interactive things, like desktop user interfaces, it is possible
 >to quietly cheat.  The measuring tool in uDig, for example, projects
 >back into geographic coordinates, and does length calculations on the
 >spheroid, rather than naively returning the length in the projected
 >plane.  In this way it is possible to measure distances in meters
 >while looking at a map in geographics, or get correct distances from
 >a map in mercator.

From: "Craig Miller" <craig at millerfam.net>
 >To get correct distances, you will need to calculated great-circle distance.

I am almost sure that I can implement one of these solutions through php 
mapscript, but it will mean circumventing the usual measuring tools . . .

If you are still interested, I will try to re-create the visible 
differences from the command line mapserv.exe as you suggest . . .

thanks again for the interest
tim

Tim Norris


At 02:47 PM 10/17/2005, Frank Warmerdam wrote:
>On 10/17/05, Kralidis,Tom [Burlington] <Tom.Kralidis at ec.gc.ca> wrote:
> > Thanks for the info.  I don't think these instances are using WKT/GML as
> > input or output, if that's what you mean.  Basic .ovf connection to
> > provide WMS output.  Is there anything we can do on our end to help with
> > this issue?  The problem is basically:
>
>Tom / Tim,
>
>If you can reproduce the problem at the commandline with mapserv.exe
>from FWTools then just bundle up the minimum data required to reproduce
>it along with the commandlne required to invoke it and submit that as a
>mapserver bug, reassigned to me.
>
>If you can't reproduce it under those circumstances then perhaps we can
>work out a clue as to what is going from that.
>
>Best regards,
>--
>---------------------------------------+--------------------------------------
>I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush    | Geospatial Programmer for Rent