[Proj] [proj4] epsg:31370 possible wrong parameters

Willy-Bas Loos willybas at gmail.com
Mon Feb 21 10:50:16 EST 2011

That explains, thanks.
Has it been fixed in the latest version of proj4 (the epsg file)?


On Mon, Feb 21, 2011 at 11:43 AM, Mikael Rittri
<Mikael.Rittri at carmenta.com>wrote:

> Hello,
> I think your parameters are nearly right, but not quite:
> the last number you have is -1, but it should be -1.2747.
> (Maybe this doesn't make a great difference in the results.)
> Apart from the this, your +towgs84 parameters agree with
> the datum shift "BD72 to WGS 84 (3)", EPSG:15929 (except
> that yours have more decimals).
> Background: I think the Belgian authorities published this
> datum shift in the opposite direction (from WGS 84 to BD72),
> which somehow made it into the proj/nad/epsg file.  That's
> why you had to reverse so many signs.
> Also, the Belgians published the last number, not as a
> scale difference in ppm, but as the scale factor 1.0000012747.
> It appears that this factor has been rounded to 1, and interpreted
> as a scale difference in ppm by proj/nad/epsg (and by postgis too),
> but it really corresponds to the scale difference 1.2747 ppm,
> or -1.2747 ppm if you go from BD72 to WGS 84.
> A further problem is that EPSG has published an erroneous
> version of this datum shift, EPSG:15749, where the scale
> difference had the wrong sign. That version was deprecated
> by EPSG in March 2007 and replaced by EPSG:15929.
> Regards,
> Mikael Rittri
> Carmenta
> Sweden
> http://www.carmenta.com
> ________________________________
> From: proj-bounces at lists.maptools.org [mailto:
> proj-bounces at lists.maptools.org] On Behalf Of Willy-Bas Loos
> Sent: den 17 februari 2011 19:47
> To: proj at lists.maptools.org
> Subject: [Proj] [proj4] epsg:31370 possible wrong parameters
> Hi, we had issues displaying data from epsg:31370
> We changed some "-" signs, according to a definition that i found in
> postgis, and that solved the issue.
> We use Rel. 4.7.1, 23 September 2009.
> The parameters that  showed us the expected result were:
> <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 <>
> 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.
> Hope this is constructive.
> Cheers,
> --
> "Patriotism is the conviction that your country is superior to all others
> because you were born in it." -- George Bernard Shaw

"Patriotism is the conviction that your country is superior to all others
because you were born in it." -- George Bernard Shaw
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