[Gvsig_english] trouble with EPSG 2154 and 27561

Fri Jul 16 15:02:04 CEST 2010

Hello, 

50m is with OADE 2010 !!! 
With gvsig 1.9 it's only 1.4 m (that is right with the precision of the datum shift) 

If I create an user CRS with a copy of 27561 where I only change the central meridian, I have the same result that with your proposal of user CRS. I think that there is a problem with meridian "non Grenwich" in lambert conformal conic 1SP. 

Regards , 

Michel Bouillot 

----- Mail Original ----- 
De: "Bouillot Michel" <michel.bouillot at montreuil.fr> 
À: "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es> 
Envoyé: Vendredi 16 Juillet 2010 11:08:16 
Objet: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hello, 

Thanks for the answer. 
The process works but I find an error of about 50m. 
I take time to study it and I tell you. 

Regards 

Michel Bouillot 

----- Mail Original ----- 
De: "Juan Lucas Dominguez Rubio" <jldominguez at prodevelop.es> 
À: "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es>, "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es> 
Envoyé: Vendredi 16 Juillet 2010 10:04:27 
Objet: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hello, Michel: 

I think there's some confusion about the meaning of the EPSG codes. According to spatialref.org, the PRJ file for EPSG:27561 is this: 

http://spatialreference.org/ref/epsg/27561/prj/ 

But that file is not like the one that comes with your shapefile. 

gvSIG is probably using the definition found in the spatialref.org website, so that's why your shapefiles do not match if you select EPSG:27561 when adding that file to your view. 

According to spatialref.org, the CRS that matches your PRJ file is 'NTF Lambert Zone 1 France 2SP' (code SR-ORG:6910): 

http://spatialreference.org/ref/sr-org/6910/prj/ 

So all you have to do is declare it as a user-defined CRS in gvSIG. 

This has worked for me (I'll refer to your files as montreuil_2154.shp and montreuil_27561.shp): 

- from the project manager, click 'New' to create a new view. Select it (without opening it) and click on 'Properties' 
- clic on the [...] button to change the view's CRS 
- choose 'Type: user CRS' and click on 'New' 
- choose the 'From WKT' option and paste this paragraph in the text box: 

PROJCS["unnamed",GEOGCS["unnamed ellipse",DATUM["unknown",SPHEROID["unnamed",6378249.2,293.4660200000053],TOWGS84[-168,-60,320,0,0,0,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["standard_parallel_1",48.5985227778],PARAMETER["standard_parallel_2",50.3959116667],PARAMETER["latitude_of_origin",49.5],PARAMETER["central_meridian",2.3372291667],PARAMETER["false_easting",600000],PARAMETER["false_northing",200000],UNIT["Meter",1],AUTHORITY["EPSG","12345"]] 

- click on 'Finalize' and 'Accept'. You'll see that gvSIG refers to the new CRS as 'USR:1' or similar. 
- click 'Accept' again and open the view 
- add the file montreuil_27561.shp without any additional option because we know it's the same CRS of the view. 
- go to the 'Add file' option again, choose the file montreuil_2154.shp and before clicking on 'Accept', click on the button to indicate the CRS of the file that is being added. Search for EPSG:2154 (this one has no problem, you can use it) and select it, then you need to choose the 'Manual transformation' option in the transformation combo box. The seven parameters are: 

168 
60 
-320 
0 
0 
0 
0 

- click 'Accept' on all the following dialogs, and both shapefiles should match. There is a small error of about 1.5 m, but I don't think that's a problem for you. 

Does this process work for you? 

The CRS you have defined should be available from now on, but you will have to type the seven parameters each time from the 'Manual transformation' option. 

Those seven parameters are valid if the view is in 'NTF Lambert Zone 1 France 2SP'. If the view is in EPSG:2154 and you add a shapefile in 'NTF Lambert Zone 1 France 2SP', you'll have to reverse the sign of the parameters. 

If you don't want to deal with user CRS and parameters inside gvSIG, you can reproject your shapefiles before starting gvSIG. There is a nice free program that does that: 

http://fwtools.maptools.org 

The command would be something like: 

ogr2ogr -f "ESRI Shapefile" -s_srs epsg:2154 -t_srs epsg:27561 new_file.shp old_file_2154.shp 

(but again, we should check the meaning of EPSG:27561 in that case) 

Regards, 

Juan Lucas Domínguez Rubio 
--- 

Prodevelop SL, Valencia (España) 

Tlf.: 96.351.06.12 -- Fax: 96.351.09.68 
http://www.prodevelop.es 
--- 

De: gvsig_internacional-bounces at listserv.gva.es en nombre de Bouillot Michel 
Enviado el: jue 15/07/2010 14:22 
Para: Users and Developers mailing list 
Asunto: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hello, 

I think that you are right. 

I join shapefiles in both EPSG. 

Thanks for the tests. 

Regards, 

Michel Bouillot 

----- Mail Original ----- 
De: "Juan Lucas Dominguez Rubio" <jldominguez at prodevelop.es> 
À: "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es>, "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es> 
Envoyé: Jeudi 15 Juillet 2010 13:29:45 
Objet: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hello, I think there's a misunderstood. 

gvSIG is able to do on-the-fly reprojection (this is what Michel needs, I think). 

But I'm afraid that, even if he follows the right steps to do it, the result will be wrong because (I think) gvSIG does not know the right parameters to perform that conversion (between EPSG:2154 and EPSG:27561). 

There have been problems with the French projections in the past, and I'm not sure if they were caused by a bug in gvSIG or in the libraries used by gvSIG (especially Proj4). 

Michel: can you please send to the list two little shapefiles (one in EPSG:2154 and the other in EPSG:27561) that should match but do not match in gvSIG? So we can also do some tests. 

Regards, 

Juan Lucas Domínguez Rubio 
--- 
Prodevelop SL, Valencia (España) 

Tlf.: 96.351.06.12 -- Fax: 96.351.09.68 
http://www.prodevelop.es 
--- 

De: gvsig_internacional-bounces at listserv.gva.es en nombre de Bouillot Michel 
Enviado el: jue 15/07/2010 13:02 
Para: Users and Developers mailing list 
Asunto: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hi, 

Thanks for this explanation. 

I find GVSIG very good but in France we have just changed of RS. We begin to have data in the 2 RS. 
The reprojection in the view would be very pactical ! 
Is there a hope for a such function in the futur ? 

Regards 

Michel Bouillot 

----- Mail Original ----- 
De: "Guillermo Tamburini" <tamburini_gui at gva.es> 
À: "Users and Developers mailing list" <gvsig_internacional at listserv.gva.es> 
Envoyé: Jeudi 15 Juillet 2010 12:43:50 
Objet: Re: [Gvsig_english] trouble with EPSG 2154 and 27561 

Hi, 

In fact, you can't correctly represent data in different reference systems in the same View (without reporojecting, it have no sense). 

There are some software applications which applies automatically the reprojection, but it is not the case in gvSIG with vector layers. 

First of all, you have to select the correct RS for your View, and then load the data (the target RS you are going to work). 

Otherwise, you will see your data but in a incorrect situation. In other utm spindle, or displaced... 

If your data is in different RS, you will have to reproject it. Goprocessing tools->Data Conversion->Reproject; the layer in the not current projection to the current projection. 

Regards 

Bouillot Michel wrote: 

Hello, 

I try to open in the same view one shp in EPSG 2154 and one SHP in EPSG 27561 but it don't match correctly. There is a problem with the X like a translation witch have a value who seems to be the difference between Greenwich and Paris meridian. 

How to correct this trouble ? 

regards 

Michel Bouillot 
Chef de projet SIG 
01 48 70 63 23 / michel.bouillot at montreuil.fr 
Ville de Montreuil / Direction Urbanisme et Habitat 
Service Études Développement Urbain 
3, rue de Rosny / 93100 Montreuil 

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-- 
Guillermo Tamburini Beliveau
Proyecto gvSIG 
Consellería de Infraestructuras y Transportes (GVA) 
Valencia (Spain) 
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