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Thanks for the informations.<br>
The two reference systems are often referred to as being identical,
and that lead me to believing so.<br>
If I understand well, the datum shift parameters are required in
order to improve the accuracy of the conversion between 3004 and
other RS as ED50 UTM33, while they are not needed for conversion
between 102092 and e.g. WGS84?<br>
Sorry if post was off topic as non strictly QGis related.<br>
Regards<br>
Paolo<br>
<br>
<div class="moz-cite-prefix">Il 07/11/2013 13:54, G. Allegri ha
scritto:<br>
</div>
<blockquote
cite="mid:CAB4g1=xctOgc7yccvSTC8zp2ROag6ZrCpGuREHXc_RVNwQpPFA@mail.gmail.com"
type="cite">
<p dir="ltr">Exactly, that's what I was saying ;) </p>
<p dir="ltr">giovanni </p>
<div class="gmail_quote">Il 07/nov/2013 13:02 <<a
moz-do-not-send="true" href="mailto:b.j.kobben@utwente.nl">b.j.kobben@utwente.nl</a>>
ha scritto:<br type="attribution">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
FWIW, the two definitions (EPSG 3004 & EPSG 102092) are
NOT the same. They<br>
do have the same projection parameters, but one has datum
shift parameters<br>
too (+towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68)
that the other<br>
is lacking. That means that when you use the one in
re-projecting data, it<br>
will be able to take into account the necessary datum-shift,
while the the<br>
other will not be able to do that. In many cases this can lead
to severe<br>
shifts in coordinates (up to several 100's of meters).<br>
<br>
Yours,<br>
<br>
--<br>
Barend Köbben<br>
ITC - University of Twente<br>
PO Box 217, 7500AE Enschede (The Netherlands)<br>
+31-(0)53 4874 253<br>
@barendkobben<br>
<br>
<br>
<br>
<br>
<br>
<br>
On 07-11-13 13:48, "G. Allegri" <<a moz-do-not-send="true"
href="mailto:giohappy@gmail.com">giohappy@gmail.com</a>>
wrote:<br>
<br>
>Roma 1940 Gauss Boaga is different in that it as a
different central<br>
>meridian.<br>
>The other two are different definitions of the same datum,
but in 3003<br>
>there re the average transformation parameters. That's why
it works<br>
>better then 102094.<br>
>In the previous email I inverted the two.<br>
><br>
><br>
>giovanni<br>
><br>
><br>
><br>
>2013/11/7 Paolo <<a moz-do-not-send="true"
href="mailto:e-paul@tiscali.it">e-paul@tiscali.it</a>><br>
><br>
>Yes, actuallyI am reprojecting rasters from Gauss Boaga
Roma 40 Monte<br>
>Mario zone 2 to ED50UTM33.<br>
>Errors are huge if I use 102092, but they are very small
using 3004.<br>
><br>
>Further research lead me to discover even more,
appearingly identical,<br>
>reference systems:<br>
>- Monte Mario Italy 2.prj (codice EPSG 3004);<br>
>- Monte Mario (Rome) Italy 2.prj (codice EPSG 26592);<br>
>- Roma 1940 Gauss Boaga Est.prj (codice EPSG 102094),<br>
><br>
>This is even more confusing, and will require some more
studying.<br>
><br>
>Regards,<br>
>Paolo<br>
><br>
>Il 07/11/2013 10:37, G. Allegri ha scritto:<br>
><br>
><br>
>As you can see, 102092 has the average transformation
parameters to<br>
>WGS84, which brings some more precision during datum
transformation. I<br>
>suppose you're reprojecting the data to some different
CRS.<br>
><br>
>giovanni<br>
>Il 07/nov/2013 08:33 "Paolo" <<a moz-do-not-send="true"
href="mailto:e-paul@tiscali.it">e-paul@tiscali.it</a>> ha
scritto:<br>
><br>
>Oops... I forgot the most important part in my first post.
Here are the<br>
>edfinitions:<br>
><br>
>EPSG 3004 - Monte Mario / Italy zone 2:<br>
>+proj=tmerc +lat_0=0 +lon_0=15 +k=0.9996 +x_0=2520000
+y_0=0 +ellps=intl<br>
>+towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
+units=m +no_defs<br>
><br>
>EPSG 102092 - Monte_Mario_Italy_2:<br>
>+proj=tmerc +lat_0=0 +lon_0=15 +k=0.9996 +x_0=2520000
+y_0=0 +ellps=intl<br>
>+units=m +no_defs<br>
><br>
>3004 works well with my data, while 102092 does not.<br>
>There appears to be a relatively large shift, in the order
of tens or<br>
>hundreds meters,monstly along the north - south direction.<br>
><br>
>Thanks<br>
>Paolo<br>
><br>
><br>
><br>
>Il 07/11/2013 00:47, G. Allegri ha scritto:<br>
><br>
><br>
>In QGIS they appear having the same definition, Could you
paste the<br>
>102092 definition that you have?<br>
><br>
><br>
>giovanni<br>
><br>
><br>
><br>
>2013/11/6 Paolo <<a moz-do-not-send="true"
href="mailto:e-paul@tiscali.it">e-paul@tiscali.it</a>><br>
><br>
>Hello,<br>
>I am a relatively recent QGIS user. I am at the moment
using version 2.0<br>
>- Dufour.<br>
>I would like to ask a simple question about two different
datums I am<br>
>experiencing problems with.<br>
>They are: EPSG 102092 and EPSG 3004.<br>
>Accordinf to my (short) research, they are supposed to be
exactly the<br>
>same datum, but the definitions in QGIS are different.<br>
>If I use 3004, the specific data set I'm using will
overlap properly with<br>
>the other datasets, but it will not if I use 102092.<br>
>Can anybody help me getting a better understanding of this
behaviour?<br>
>Thanks<br>
>Paolo<br>
>_______________________________________________<br>
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target="_blank">http://lists.osgeo.org/mailman/listinfo/qgis-user</a><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
>--<br>
>Giovanni Allegri<br>
><a moz-do-not-send="true"
href="http://about.me/giovanniallegri" target="_blank">http://about.me/giovanniallegri</a><br>
>blog: <a moz-do-not-send="true"
href="http://blog.spaziogis.it" target="_blank">http://blog.spaziogis.it</a><br>
>GEO+ geomatica in Italia <a moz-do-not-send="true"
href="http://bit.ly/GEOplus" target="_blank">http://bit.ly/GEOplus</a><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
>--<br>
>Giovanni Allegri<br>
><a moz-do-not-send="true"
href="http://about.me/giovanniallegri" target="_blank">http://about.me/giovanniallegri</a><br>
>blog: <a moz-do-not-send="true"
href="http://blog.spaziogis.it" target="_blank">http://blog.spaziogis.it</a><br>
>GEO+ geomatica in Italia <a moz-do-not-send="true"
href="http://bit.ly/GEOplus" target="_blank">http://bit.ly/GEOplus</a><br>
<br>
</blockquote>
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