<div>That explains, thanks.</div>Has it been fixed in the latest version of proj4 (the epsg file)?<div><br></div><div>WBL<br><br><div class="gmail_quote">On Mon, Feb 21, 2011 at 11:43 AM, Mikael Rittri <span dir="ltr"><<a href="mailto:Mikael.Rittri@carmenta.com">Mikael.Rittri@carmenta.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Hello,<br>
I think your parameters are nearly right, but not quite:<br>
the last number you have is -1, but it should be -1.2747.<br>
(Maybe this doesn't make a great difference in the results.)<br>
<br>
Apart from the this, your +towgs84 parameters agree with<br>
the datum shift "BD72 to WGS 84 (3)", EPSG:15929 (except<br>
that yours have more decimals).<br>
<br>
Background: I think the Belgian authorities published this<br>
datum shift in the opposite direction (from WGS 84 to BD72),<br>
which somehow made it into the proj/nad/epsg file. That's<br>
why you had to reverse so many signs.<br>
<br>
Also, the Belgians published the last number, not as a<br>
scale difference in ppm, but as the scale factor 1.0000012747.<br>
It appears that this factor has been rounded to 1, and interpreted<br>
as a scale difference in ppm by proj/nad/epsg (and by postgis too),<br>
but it really corresponds to the scale difference 1.2747 ppm,<br>
or -1.2747 ppm if you go from BD72 to WGS 84.<br>
<br>
A further problem is that EPSG has published an erroneous<br>
version of this datum shift, EPSG:15749, where the scale<br>
difference had the wrong sign. That version was deprecated<br>
by EPSG in March 2007 and replaced by EPSG:15929.<br>
<br>
Regards,<br>
Mikael Rittri<br>
Carmenta<br>
Sweden<br>
<a href="http://www.carmenta.com" target="_blank">http://www.carmenta.com</a><br>
<br>
________________________________<br>
<br>
From: <a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a> [mailto:<a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a>] On Behalf Of Willy-Bas Loos<br>
Sent: den 17 februari 2011 19:47<br>
To: <a href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</a><br>
Subject: [Proj] [proj4] epsg:31370 possible wrong parameters<br>
<div><div></div><div class="h5"><br>
<br>
Hi, we had issues displaying data from epsg:31370<br>
We changed some "-" signs, according to a definition that i found in postgis, and that solved the issue.<br>
We use Rel. 4.7.1, 23 September 2009.<br>
<br>
The parameters that showed us the expected result were:<br>
<31370> +proj=lcc +lat_1=51.16666723333333 +lat_2=49.80333339 +lat_0=90 +lon_0=4.367486666666666 +x_0=150000.013 +y_0=5400088.438 +ellps=intl +units=m +towgs84=-106.868628,52.297783,-103.723893,0.336570,-0.456955,1.842183,-1 +no_defs <><br>
<br>
The minus signs and the versions in the several packages in which proj4 is included is getting me a bit dazzled, so i might be mistaken.<br>
<br>
Hope this is constructive.<br>
Cheers,<br>
<br>
WBL<br>
<br>
--<br>
"Patriotism is the conviction that your country is superior to all others because you were born in it." -- George Bernard Shaw<br>
<br>
</div></div></blockquote></div><br><br clear="all"><br>-- <br>"Patriotism is the conviction that your country is superior to all others because you were born in it." -- George Bernard Shaw<br>
</div>