[MAPSERVER-USERS] how mapserver handles different datum projections

[DNC]

Frank,

Is there a way to add the towgs84 definition in the map file?

When I try that MS gives an error:
msProcessProjection(): Projection library error. no options found in
'init' file

The projection definition is this:
'init=epsg:27492 towgs84=-223.237,110.193,36.649'

Thanks,
Duarte


Frank Warmerdam-2 wrote:
> 
> DNC wrote:
>> Hi all.
>> 
>> Can anyone clarify how mapserver handles different datum in the map
>> projection and in the layers projection when serving a wms service?
>> Does MS apply datum transformations? If not, can it be done somehow
>> without
>> converting the layers?
>> 
>> In my case I'm working with vector data, and have defined a map
>> projection
>> using "init=epsg:code" syntax. Then at the layer level I use the same
>> syntax
>> to declare the projection the data is in. 
>> And finally I want my WMS service to be published in 3 different datum
>> and
>> for that I advertise several epsg codes in the "wms_srs" metadata entry.
>> 
>> I'm noticing a shift in images produced by MS that indicate a datum shift
>> is
>> not being applied. What can be done?
> 
> Duarte,
> 
> In general MapServer will apply a datum shift if you have datum
> definitions
> for the source and destination coordinate system.  But often the
> definitions
> in the EPSG init file lack datum shift info and so nothing is done.
> 
> So, start by examining the PROJ.4 definitions in the "epsg" init file and
> see if they have +towgs84= or +nadgrids directives.  You might also want
> to
> skim the material in the PROJ.4 FAQ about datums.
> 
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
> 
> _______________________________________________
> mapserver-users mailing list
> mapserver-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users
> 
> 

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