Coordinate Projects

[Gayani]

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
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[Frank Warmerdam-2]

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
>

Gayani,

Presuming that the projection method is Transverse Mercator you could use
a PROJECTION block like:

PROJECTION
   "+proj=tmerc +lon_0=80.771713 +k=0.999924 +lat_0=7.000472 +x_0=200000
+y_0=20000 +units=m +a=6377276.3449999997 +b=6356075.4131402401"
END

I am not familiar with your coordinate system but a simplistic attempt to look
it up in the EPSG coordinate system failed.  So it might be hard to deploy
a WMS based on it since that depends on knowing an EPSG code.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@...
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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[Jeff McKenna]

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:
http://spatialreference.org/ref/?search=sri+lanka&srtext=Search


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:

PROJECTION
        "proj=utm"
        "zone=44"
        "a=6377276.345"
        "b=6356075.41314024"
         "lat_0=7.000472"
         "lon_0=80.771713"
         "k_0=0.999924"
         "x_0=200000"
         "y_0=200000"
         "rf=300"
        "units=m"
        "no_defs"
END

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

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/


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[Frank Warmerdam-2]

Jeff McKenna wrote:

> PROJECTION
> "proj=utm"
> "zone=44"
> "a=6377276.345"
> "b=6356075.41314024"
>          "lat_0=7.000472"
>          "lon_0=80.771713"
>          "k_0=0.999924"
>          "x_0=200000"
>          "y_0=200000"
>          "rf=300"
> "units=m"
> "no_defs"
> END

Jeff has some excellent suggestions, but I must clarify that you
should not mix proj=utm with specific settings of lat_0 and lon_0.
When your lat_0 and lon_0 are not the default for a given utm zone
you should instead just use proj=tmerc and specify all the parameters.

Honestly, I was suprised to see "utm zone 44" when the parameters
are so *not* UTM 44.  The lat_0, lon_0, x_0, y_0 and k values are all
different than UTM 44.

> 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.

Yes, I believe +rf= is the right parameter, but the ellipse is also fully
specified with +a and +b (semi-major and semi-minor) axes.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@...
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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