[Mapserver-users] On-The-Fly Projection

[Frank Warmerdam]

Shaik A. Hussain wrote:
> Greetings,
> 
>             I am having problem with On-The-Fly-Projection. I am using mapserver 3.6.4, windows 2000, apache.
> 
> My out put image projection is in Pennsylvania Polyconic,  other layers with different projection spaces, one in PA Albert Conic, Geographic and PA State Plan South NAD27. 
> 
> The layer which has PA State plan south nad27 is not showing , other layers are showing correctly.  Does any one help me what is wrong with the Projection definition for the PA State plan.
> 
> Here is my map projection definitions. 
> 
> Out put image projection definition at map level is PENNSYLVANIA POLYCONIC.
> 
>  PROJECTION
>     "proj=poly"
>     "ellps=GRS80"
>     "lon_0=77.75w"
>     "lat_0=40.925n"
...
>       PROJECTION
>            "proj=lcc"
>            "ellps=clrk66"
>            "lat_1=39.933333333n"
> 	   "lat_2=40.800000000n" 
> 	   "lat_0=39.333333333n" 
> 	   "lon_0=77.750000000w" 
> 	   "x_0=609601.219" 
>            "y_0=0.000"
>           # "to_meter=0.3048006096"
>            "datum=NAD27"	 
>            "no_defs"

Anwar,

I believe the issue is that you were not specific about the datum of the
polyconic projection at the map level, so the projections library is unsure
of how to translate the NAD27 stateplace layer.  Try setting datum=NAD83
instead of ellps=GRS80 on the map level and see if that helps.  Note that
you will need to ensure that the datum grid shift files are accessable for
this to work properly.  You should hopefully have a file call "conus"
somewhere, and you need to ensure that the PROJ_LIB environment variable
points to where it is if it is not in the default location
(/usr/local/share/proj).

To see if this is a datum problem or something else you might want to just
try setting the map datum to NAD27 (and dropping the ellps) initially, then
set it properly to NAD83 to add the grid shifting step.

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    | Geospatial Programmer for Rent