Projection

[Rhys Ickeringill]

G'day Dirk-Jan,

My comments below:

----- Original Message -----
From: "Dirk-Jan Huisman" <d.huisman at INGBCC.NL>
To: <MAPSERVER-USERS at LISTS.UMN.EDU>
Sent: Friday, March 11, 2005 2:08 AM
Subject: [UMN_MAPSERVER-USERS] Projection


Hi all,


My projection(British_National_Grid) file should be something like this:
  PROJECTION
    "proj=tmerc"
    "lat_0=49"
    "lon_0=-2"
    "x_0=400000"
    "y_0=-100000"
    "k=0.999601272"
    "ellps=Airy_1830"
    "datum=D_OSGB_1936"
    "to_meter=1"
    "no_defs
  END

I'm using Windows2000 and Apache.

With the install of Mapserver I copy proj/nad to C:\

I have an unknown elliptical parameter ("ellps=Airy_1830") and unknown
datum parameter("datum=D_OSGB_1936").

----- End Message -----

Just had a quick look at the Proj data files and I think your ellps
parameter should be just "airy" rather than "Airy_1830". Your datum
"OSGB_1936" is not defined anywhere as a *named* datum. AFAIK since you're
providing all the other parameters (false eastings, northings, scale factors
etc.), you don't need to have a datum parameter anyway - it just duplicates
the definition of those parameters.

Actually, I think you can replace your entire projection statement with
just:

PROJECTION
    "init=epsg:27700"
END

Personally I still prefer the long version like you were using:

  PROJECTION
    "proj=tmerc"
    "lat_0=49"
    "lon_0=-2"
    "x_0=400000"
    "y_0=-100000"
    "k=0.999601272"
    "ellps=airy"
    "to_meter=1"
    "no_defs
  END


If you're still being told that the ellipsoid you've specified can't be
found, try specifying its' parameters directly (ie. specify two from:
{semi-major axis, semi-minor axis, eccentricity, inverse flattening, ...})

HTH

- Rhys