FWIW, the two definitions (EPSG 3004 & EPSG 102092) are NOT the same. They do have the same projection parameters, but one has datum shift parameters too (+towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68) that the other is lacking. That means that when you use the one in re-projecting data, it will be able to take into account the necessary datum-shift, while the the other will not be able to do that. In many cases this can lead to severe shifts in coordinates (up to several 100's of meters).
Yours, -- Barend Köbben ITC - University of Twente PO Box 217, 7500AE Enschede (The Netherlands) +31-(0)53 4874 253 @barendkobben On 07-11-13 13:48, "G. Allegri" <gioha...@gmail.com> wrote: >Roma 1940 Gauss Boaga is different in that it as a different central >meridian. >The other two are different definitions of the same datum, but in 3003 >there re the average transformation parameters. That's why it works >better then 102094. >In the previous email I inverted the two. > > >giovanni > > > >2013/11/7 Paolo <e-p...@tiscali.it> > >Yes, actuallyI am reprojecting rasters from Gauss Boaga Roma 40 Monte >Mario zone 2 to ED50UTM33. >Errors are huge if I use 102092, but they are very small using 3004. > >Further research lead me to discover even more, appearingly identical, >reference systems: >- Monte Mario Italy 2.prj (codice EPSG 3004); >- Monte Mario (Rome) Italy 2.prj (codice EPSG 26592); >- Roma 1940 Gauss Boaga Est.prj (codice EPSG 102094), > >This is even more confusing, and will require some more studying. > >Regards, >Paolo > >Il 07/11/2013 10:37, G. Allegri ha scritto: > > >As you can see, 102092 has the average transformation parameters to >WGS84, which brings some more precision during datum transformation. I >suppose you're reprojecting the data to some different CRS. > >giovanni >Il 07/nov/2013 08:33 "Paolo" <e-p...@tiscali.it> ha scritto: > >Oops... I forgot the most important part in my first post. Here are the >edfinitions: > >EPSG 3004 - Monte Mario / Italy zone 2: >+proj=tmerc +lat_0=0 +lon_0=15 +k=0.9996 +x_0=2520000 +y_0=0 +ellps=intl >+towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68 +units=m +no_defs > >EPSG 102092 - Monte_Mario_Italy_2: >+proj=tmerc +lat_0=0 +lon_0=15 +k=0.9996 +x_0=2520000 +y_0=0 +ellps=intl >+units=m +no_defs > >3004 works well with my data, while 102092 does not. >There appears to be a relatively large shift, in the order of tens or >hundreds meters,monstly along the north - south direction. > >Thanks >Paolo > > > >Il 07/11/2013 00:47, G. Allegri ha scritto: > > >In QGIS they appear having the same definition, Could you paste the >102092 definition that you have? > > >giovanni > > > >2013/11/6 Paolo <e-p...@tiscali.it> > >Hello, >I am a relatively recent QGIS user. I am at the moment using version 2.0 >- Dufour. >I would like to ask a simple question about two different datums I am >experiencing problems with. >They are: EPSG 102092 and EPSG 3004. >Accordinf to my (short) research, they are supposed to be exactly the >same datum, but the definitions in QGIS are different. >If I use 3004, the specific data set I'm using will overlap properly with >the other datasets, but it will not if I use 102092. >Can anybody help me getting a better understanding of this behaviour? >Thanks >Paolo >_______________________________________________ >Qgis-user mailing list >Qgis-user@lists.osgeo.org >http://lists.osgeo.org/mailman/listinfo/qgis-user > > > > > > > >-- >Giovanni Allegri >http://about.me/giovanniallegri >blog: http://blog.spaziogis.it >GEO+ geomatica in Italia http://bit.ly/GEOplus > > > > > > > > > > > > > > > > > > > > >-- >Giovanni Allegri >http://about.me/giovanniallegri >blog: http://blog.spaziogis.it >GEO+ geomatica in Italia http://bit.ly/GEOplus _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user