[Mapserver-users] Lambert Projection for Europe

[Jan Hartmann]

Hi Steffen,

The Lambert Conformal Conic Projection can set four parameters:

lon_0: central longitude, default 0
lat_0: central latitude, default 0
lat_1: latitude of first intersection of the projection cone
        (default 33N)
lat_2: latitude of second intersection of the projection cone
        (default 45N)

According to the PROJ manual (http://www.remotesensing.org/proj/) the 
last two default values are normally used for maps of the coterminous 
USA. For Europe I use for lon_0 and lat_0 both 10 , and for lat_1 and 
lat_2 45 and 55. You can experiment a bit to get the most pleasing 
effect. lon_0 displaces the map east-west, lat_0 north-south, while 
lat_1 and lat_2 influence the way meridians converge to the north or south.

The coordinates are integers, I think meters. I use
-20000000 -10000000 / 20000000 10000000 for the whole world. For Europe 
I generally use an extent of -1000000 3000000 3000000 7000000. In terms 
of the MapFile:

extent -1000000 3000000 3000000 7000000
projection
   "proj=lcc"
   "lon_0=10"
   "lat_0=00"
   "lat_1="45"
   "lat_2="55"
end

This projection is conformal, which means that angles are correct, while 
surface and distance are distorted. These projections are much used for 
navigation systems. For statistical maps you are better off with equal 
area projections. On a European scale, it does not make much difference 
though.

For your better understanding , I quote the explanation of different 
projection types from a German cartography handbook in my library 
(Günter Hake, Kartographie I, Göschen 1982, p. 128):

Man kann daher zwischen flächentreuen, konformen, teilweise längentreuen 
und vermittelnden (ohne besondere Eigenschaften) Abbildungen 
unterscheiden. Dabei ist zu beachten dass Flächentreuen und partielle 
Längentreue auch im Endlichen auftreten können, während die Winkeltreue 
als Konformität stets nur im unendlich Kleinen bestehen kann.

I wonder what Google would make of that!

Cheers,

Jan


Steffen Gebhardt wrote:
> Hi to all,
> 
> I want to display my layers, which are all in geographic projection 
> (latlong), in Lambert Conformal Conic Projection (lcc). I have data os whole 
> europe, and by now I display them as "latlong". 
> Since I find no help and examples for that I need to ask you for some help. 
> How do I have to define the global projection?
> 
> Like this:
> PROJECTION
>  "proj=lcc"
> END
> ?
> Or do I have to specify more attributes? What about the unit and the 
> mapextent?
> 
> Thanks for the help.
> 
> Steffen 
> _______________________________________________
> Mapserver-users mailing list
> Mapserver-users at lists.gis.umn.edu
> http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
>