[Gvsig_english] EPSG 27572

[Juan Lucas Dominguez Rubio]

Hello, Stéphane,
 
OK.
 
Here are some things I have found that might be useful to you. I don't know much about cartography, so don't take these hints as necessarily true:
 
- This a partial port to Java of Proj4:
 
http://www.jhlabs.com/java/maps/proj/
 
It does not allow transformations, only peforms geographic-projected/projected-geographic conversion within the same datum, so it's only part of the job. That package has a class called LambertConformalConicProjection.java which I think is the one that interests you, but be careful with it: perhaps it's assuming that you are interested in the projections used in some states of the United States, and some parameters might be set by default to a value which is not the one used in France. Besides, take a look at the definition of EPSG:27572 used by that package:
 
# NTF (Paris) / Lambert zone II
<27572> +proj=lcc +lat_1=46.8 +lat_0=46.8 +lon_0=0 +k_0=0.99987742 +x_0=600000 +y_0=2200000 +a=6378249.2 +b=6356515 +towgs84=-168,-60,320,0,0,0,0 +pm=paris +units=m +no_defs  <>
 
- The French IGN currently publishes their general national 3-parameter transformation from NTF to WGS84 as: dX = +168 m, dY = +60 m, dZ = -320 m.
 
- This is the content of a valid PRJ file for EPSG:27572:
 
PROJCS["NTF (Paris) / Lambert zone II",GEOGCS["NTF (Paris)",DATUM["D_NTF",SPHEROID["Clarke_1880_IGN",6378249.2,293.4660212936265]],PRIMEM["Paris",2.33722917],UNIT["grad",0.01570796326794897]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["latitude_of_origin",52],PARAMETER["central_meridian",0],PARAMETER["scale_factor",0.99987742],PARAMETER["false_easting",600000],PARAMETER["false_northing",2200000],UNIT["Meter",1]]
 
It says lat. of origin = 52, but I think it means decimal degrees (the latitude of the north pole is 100 degrees in that unit) so it would be lat. of origin = 46.8 in standard degrees.
 
Good luck!
Juan Lucas
 

________________________________

De: gvsig_internacional-bounces at runas.cap.gva.es en nombre de Stéphane Falck
Enviado el: jue 07/08/2008 17:57
Para: gvsig_internacional at runas.cap.gva.es
Asunto: RE: [Gvsig_english] EPSG 27572



Hi Juan Lucas,

Yes, I've found some interesting piece of code which told me that all
the calculation is in pure Java written
For example :
..\libFMap\src\es\prodevelop\geodetic\utils\conversion\ConversionCoords.java

That's why I decided to post my message.

So I'm programming the method
public double[] epsg4326_to_epsg27572(double lon, double lat);

Then after testing the code of the method and make sure everything would
be alright, I would appreciate your help to modify the code.

I'll also try to compile the source code according information I'll find
in the documentation for developer.

Thank you for your help

Stéphane

 > Hello, Stéphane,

 > As you know, gvSIG Mobile does not reproject vector layers. It simply
 > reprojects the GPS coordinates to the view's coordinate system so
that > the GPS cursor is placed properly on the map.

 > The first release of gvSIG Mobile is not using any library to perform
 > this operation. All the calculation is in pure Java written by us,
and > currently the list of known coordinate systems cannot be extended
by  > the user. If you want to add EPSG:27572 to that list, you have to
 > compile the application yourself from the source code:

 >
http://www.gvsig.gva.es/fileadmin/conselleria/images/Documentacion/descargas_mobile/fuentes/ws_gvsig_mobile_0.1.0_bn44.zip

 > and you will have to implement the body of this method:

 > public double[] epsg4326_to_epsg27572(double lon, double lat);

 > If you can make that method work on Windows Mobile, I will help you
 > modify the code and you will have your extended version of gvSIG
 > Mobile, compiled by you, of course.

 > I still don't know if future versions of gvSIG Mobile will support a
 > wide range of coordinate systems.

 > Regards,

 > Juan Lucas Domínguez Rubio
 > Prodevelop SL, Valencia (España)
 > Tlf.: 96.351.06.12 -- Fax: 96.351.09.68
 > http://www.prodevelop.es <http://www.prodevelop.es/>  <http://www.prodevelop.es/>

--

Stéphane Falck

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