[Mapserver-users] Can't seem to get the projection correct

[Ed McNierney]

Daniel -

Interesting - thanks for that data!  I have to say that the MapInfo
image appears "stretched" vertically, while the MapServer image appears
correct based on having seen such projections before.

And based on some old-fashioned pixel-counting, that seems to be the
case.  I just took a careful look at your MapInfo image.  If it is
indeed in "geographic" projection, then all degrees of latitude and all
degrees of longitude are the same size.  Looking at latitude, I measured
Manitoba, which conveniently runs from 49 degrees North to 60 degrees
North.  That's 11 degrees of latitude, and Manitoba is 108 pixels high
on your image.  So your vertical scale is just under 10 pixels per
degree.

For longitude, I measured Colorado and Utah together.  They run from 102
degrees West (CO/KS border) to 114 degrees West (UT/NV border).  That's
12 degrees of longitude, but they're only 86 pixels apart.  That's a
horizontal scale of just over 7 pixels per degree.

Your MapServer image isn't squished, it's your MapInfo image that's
stretched.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242  Fax: (978) 251-1396
ed at topozone.com


-----Original Message-----
From: Daniel Morissette [mailto:morissette at dmsolutions.ca] 
Sent: Tuesday, February 18, 2003 12:20 PM
To: Martin, Daniel
Cc: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] Can't seem to get the projection correct

"Martin, Daniel" wrote:
> 
> Well, perhaps MapInfo is lying to me, but it says the projection I am
after
> *is* latlong.  It says:  "Latitude/Longitude (NAD 27 for the
Continental
> US)"
> 

If I remember well, in MapInfo, when you resize your map window, the
geographical extents are not changed, but instead the data is stretched
to fit in the new width/height aspect ratio of the view window...so you
can get any kind of vertical stretch or horizontal stretch in MapInfo
just by resizing the map window.  OTOH, MapServer will adjust the
geographical extent to produce square pixels, so as you change your view
width and height the map always looks the same.

-- 
------------------------------------------------------------
 Daniel Morissette               morissette at dmsolutions.ca
 DM Solutions Group              http://www.dmsolutions.ca/
------------------------------------------------------------
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