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

[Jan Hartmann]

Hi Thibaut,

Why did they do this in 2005? In Holland we still use the RD system with 
the Bessel ellipse. Nowadays, there is no problem at all in converting 
from whatever projection and datum to WGS84. Before 2005 you had to 
convert from Lambert 1972, after that from Lambert 2005, and now you 
have to add 500000 to each coordinate. Given that you can convert from 
every system, why going to the hassle of changing the datun and zero 
point of an existing Lambert system, only to end up with something that 
also has te be converted to WGS84?

Jan

On 28-1-2010 9:20, Thibaut Gheysen wrote:
> 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 
> <mailto: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 <mailto:j.l.h.hartmann at uva.nl>>
>     > To: "PROJ.4 and general Projections Discussions"
>     > <proj at lists.maptools.org <mailto:proj at lists.maptools.org>>
>     > Cc: "OvV_HN" <ovv at hetnet.nl <mailto: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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