[mapserver-users] projection info request Nad83 & wgs84

[Ed McNierney]

Dave -

NAD83 and WGS84 are datums, not projections.  That means you need a bit
more information.  You mention zones, which indicates the projection is
probably UTM, using NAD83 or WGS84 as the datum (UTM can be cast upon a
variety of datums).

Presumably the maps are all located in North America, since that's where
the NAD83 datum is used.  In North America, the difference between the
NAD83 and the WGS84 datums is so very small that virtually all
applications treat them as identical.  The difference is often a matter
of millimeters.  Unless you are mapping very high-accuracy points on a
very large-scale map, you should completely ignore the difference and
treat all the data as the same datum.  It's extremely likely that the
errors/uncertainty in your data are FAR larger than the difference in
the datums.

Roughly speaking, you would need to zoom in until a typical full-screen
map showed a square about 50 centimeters on a side (that is, around 20
inches by 20 inches of the Earth) before the difference in the two
datums would cause the location of a mapped point to move by a single
pixel.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242


-----Original Message-----
From: David Armstrong [mailto:david.armstrong at ntlworld.com]
Sent: Tuesday, December 18, 2001 6:30 AM
To: mapserver list
Subject: [mapserver-users] projection info request Nad83 & wgs84 


Could someone on the list please help with the correct projection info ,
i need to setup mapserver with the following projection , to help
another
lister with a project
but as i am located in the UK i am not familar with nad83 , although it
looks as if i am learning !!

the principal maps are in nad83 ( not sure of the zone yet !)

i need to set up the output projection to nad83 ( i think )
then set the map layers to nad83

also required is to set one layer to WGS84 ( gps layer )
and hope it all fits !

anyone have a similar projection requirement that can give me the
correct
projection info for the map file
any advice is appriciated

Kind Regards
Dave