lcc's and EDIGEO files

Admin. scarab JMR5322 scarab at cisi.cnes.fr
Wed Aug 23 08:00:00 EDT 1995



Dear all,

After these readings on .NTF Files, we can say we have in France the same kind 
of problem with our National Supplier IGN, who chose to promote EDIGEO format f
iles at European level. EDIGEO is an extension / modification of DIGEST formats
, and have a very *rich* (even overwhelming) description capability.
Is there anyone who knows of (free) converters from EDIGEO format files to, say
, digest or dxf or dlg format files?

By the way, to those that might be interested, i can give the **right** values 
for the French Lcc's parameters (three main zones) :

IGN uses a slightly modified (from English one) Clarke 80 ellipsoid with:

a= 6378249.2 m
b= 6356515.0 m

Paris meridian value is (in degrees) 2.337229169933865 (isn't it precise?)
and is the origine meridian for L1, L2 and L3 Projections

then for L1 : Fo = 49.5, K=.9998774 (tangent cone)
this is equivalent to secant cone with:
F1=48.59852391463664
F2=50.39591057734454

for L2 : Fo = 46.8 ; K (s a bef)
or 
F1 = 45.89891789020502
F2 = 47.69601556419748

and L3 :
Fo = 44.1 same K
or
F1 = 43.19928964391068
F2 = 44.99609523150318

Angular values in meters;

Translations are given for the three of them :
X0 = 600 000 m
Y0 = 200 000 m

Now, to apply this, and do conversions between Locations, there is a special va
lue to put in the WIND file at the proj parameter : 99 (i think for Grass4.1).
Don't know how to take the real values of the ellipsoid. However with the engli
sh clarke 80 there will be a *very* slight difference in locations.

Note that with these values you should be precise at nearly molecular scale !!

Jean Michel Roques





More information about the grass-user mailing list