[Qgis-user] Difference: EPSG 3004 - EPSG 102092

[b.j.kobben at utwente.nl]

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" <giohappy at 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
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>2013/11/7 Paolo <e-paul at 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-paul at 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-paul at 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
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>-- 
>Giovanni Allegri
>http://about.me/giovanniallegri
>blog: http://blog.spaziogis.it
>GEO+ geomatica in Italia http://bit.ly/GEOplus
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>-- 
>Giovanni Allegri
>http://about.me/giovanniallegri
>blog: http://blog.spaziogis.it
>GEO+ geomatica in Italia http://bit.ly/GEOplus