Projection Need Help

Ed McNierney ed at TOPOZONE.COM
Mon Aug 22 11:38:21 EDT 2005


Vdharan -

Use of the lat/lon projection is, IMHO, generally a very bad idea.  It
can create important distortion and makes it impossible to do something
as simple as put a meaningful scalebar on the map.

The UTM and DLTM projections are both Transverse Mercator projections,
with similar properties.  In your case, you would have data in UTM Zone
39, with a central meridian of 57 degrees East.  The DLTM is exactly the
same projection, with the central meridian at 55 degrees 20 minutes
East.  This is a very small difference, and most non-technical users
will never notice the difference.

The choice of projection depends on the area you need to cover.  If you
are only going to be mapping Dubai, or only the UAE, then I'd recommend
you choose the DLTM projection.  That would be the standard projection
in use for official Dubai or UAE data sets, and might make it easier to
integrate future data from those sources.

If, however, you intend to cover a larger area, the UTM would be a
better choice.  The DLTM projection would not be used outside of the
UAE, and if you're covering several independent countries there's no
particular reason to choose one "national" projection over another.  A
"regional" projection such as UTM would probably be a better choice.

There is really very little practical difference between these two
projections; it's just a matter of where your application will be used.

	- Ed

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

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of vdharan
Sent: Monday, August 22, 2005 8:07 AM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: [UMN_MAPSERVER-USERS] Projection Need Help

Hi

Iam using MapServer (php mapscript)for Online vehicle tracking
system.Iam also using rosa applet to show online movement of multiple
vehicles on the map.

The application is going to be used in Midddle East. While designing the
system I have used some sample shape files for that region with lat long
projection. Now are trying to get shape files with all road level
details.
The map vendor has got maps with WGS84 UTM and WGS84 DLTM(Dubai Local
Transverse Mercator) projections. I dont know which projection to select
for my application. I have used lat long projection and developed the
application.I need to pinpoint the vehicle location based lat & long. If
I go for UTM will that involve changs in the mapping codes?.  Iam from
electronics background, I could not understand much on projection.
Please Help me.

Best Regards,
vdharan



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