[Proj] Belge 1972 / Belgian Lambert 72 (31370) -towgs84parameters

[Thibaut Gheysen]

Hi,

The development of the Lambert coordinate system 2005 follows the
introduction of ETRS89 in Europe. From 1989 to 2002, the IGN has reviewed
the national geodetic network using the GPS network. This changes has led to
the Lambert 2005 projection. For a given location, the difference between
the coordinates in Lambert 1972 and 2005 are relatively low (+ / - 1
kilometer). Considering this small difference, when we received map data in
Lambert 2005 without the coordinate system used has been specified, you
might think, if you don't pay too much attention, that the data were still
in Lambert 1972. Therefore, the IGN has added 500 kilometers in X and Y
(Lambert 2008) : you see thus immediately that the projection system used is
no longer the Lambert 1972.

Thibaut.


2010/1/27 Jan Hartmann <j.l.h.hartmann at uva.nl>

>
> Nice. Our Belgian friends seem to have changed their national
> projection. I don't understand this page (Dutch:
> http://www.ngi.be/FR/FR4-4.shtm; French:
> http://www.ngi.be/FR/FR2-1-7.shtm, no English need apply). It says:
>
> "Due to the too small deviation (1 kilometer) between the coordinates of
> the Lambert 1972 projection and those of the Lambert 2005 projection,
> the NGI has changed the parameters of the Lambert 2005 projection, and
> created the Lambert 2008 projection".
>
> What they did was just adding 499.000 to both x and y coordinates of
> Lambert 2005.
>
> Lambert 1972 is the projection as defined in PROJ's epsg file (nr
> 31370), derived from the EPSG database (coordinate reference nr 411).
> Its datum is intl (=Hayford). First standard parallel is 51.166667,
> second standard parallel 49.833333, central parallel 90 (?), central
> meridian 4.367486666. x_0 = 150000.01256, y_0 = 5400088.4378
>
> Lambert 2005, as defined on the above page (nothing in the EPSG
> database): datum GRS80 (=WGS84, approximately). First standard parallel
> 51.166667, second standard parallel 49.833333, central parallel
> 50.7977777, central meridian 4.35916666666. x_0 = 150328, y_0 = 166262
>
> Lambert 2008 is Lambert 2005 Hi,with 499 km added to both x and y
> coordinates
>
> So, without additional information, I really don't see the relationship
> between the 1972, 2005 and 2008 systems. What's the difference between
> 1972 and 2005, and why did they add 500 km in 2008? Did they change each
> and every coordinate on each and every Belgian map in 2005 and are they
> changing it again in 2008? Has anyone ever seen a Lambert 2005
> coordinate? They are not in the EPSG database.
>
> If anyone can make sense of this gobbledygook, I would be happy to know.
>
> Jan
>
>
>
>
> On 27-1-2010 20:12, OvV_HN wrote:
> >
> > ----- Original Message ----- From: "Jan Hartmann" <j.l.h.hartmann at uva.nl
> >
> > To: "PROJ.4 and general Projections Discussions"
> > <proj at lists.maptools.org>
> > Cc: "OvV_HN" <ovv at hetnet.nl>
> > Sent: Wednesday, January 27, 2010 7:59 PM
> > Subject: Re: [Proj] Belge 1972 / Belgian Lambert 72 (31370)
> > -towgs84parameters
> >
> >
> >> Thanks Oscar, good to know. How did you find this page? Is it
> >> reachable from within the ngi site or did you find it with Google.
> >>
> >> Jan
> >>
> >
> >
> > The path starting from the Dutch language home page is:
> > home > know-how > geodetische diensten > Lambert 2008
> > http://www.ngi.be/NL/NL2-1-7.shtm
> >
> > Scroll down to:
> > "Relatie tussen de geodetische referentiesystemen van 1972 en 2008"
> > ...
> > "> uitgebeider schema in pdf"
> >
> > This last link goes to the page I mentioned.
> >
> >
> > Oscar van Vlijmen
> >
> >
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