[MS4W-Users] Coordinate Projects

Jeff McKenna jmckenna at gatewaygeomatics.com
Wed Nov 11 12:40:26 EST 2009

Gayani Edirisinghe wrote:
> Dear all,
>   I am using maps of sri Lanka UTM 44 Kadawala Projection values are below.
> Semimajor Axis: 6377276.344999999700000000
>     Semiminor Axis: 6356075.413140240100000000
>     Inverse Flattening: 300.801699999999980000
> False_Easting: 200000.000000
> False_Northing: 200000.000000
> Central_Meridian: 80.771713
> Scale_Factor: 0.999924
> Latitude_Of_Origin: 7.000472
> Linear Unit: Meter (1.000000)
> Please tell me how I could change the map server to display correct coordinate
> Thank You
> Gayani Edirisnghe

Hello Gayani,

Projections are a difficult issue.  The easy way to avoid this problem 
is to have all of your data in this same projection, and then you don't 
have to define any projection objects in your mapfile.

But if you want to reproject your data, either through MapServer or 
through something like the ogr2ogr utility, then you'll either need the 
projection's EPSG code or specify its PROJ.4 parameters.

I have checked MS4W's epsg file (/ms4w/proj/nad/epsg) and I don't see 
your exact projection.

A nice (and relatively new) resource for finding existing projection 
definitions is spatialreference.org  For example, if I search for "sri 
lanka" these are the results: 

The first result (http://spatialreference.org/ref/sr-org/6684/mapfile/) 
seems somewhat similar to your projection.  Using that as a start, and 
the PROJ.4 reference page for what each parameter stands for 
(http://trac.osgeo.org/proj/wiki/GenParms) my guess of your projection 
definition is:


You would place that in the LAYER section of your mapfile.

I am not sure of how to specify the "Inverse Flattening" value, so I 
have guessed that it is the "rf" parameter, but I am not sure. 
Hopefully someone else can correct me here.  Also, the experts live on 
the Proj mailing list (http://lists.maptools.org/mailman/listinfo/proj) 
so if no one else can help you, you should ask there also.

Hope this helps a little, or gets you started in the right direction.


Jeff McKenna
FOSS4G Consulting and Training Services

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