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Hi Thibaut,<br>
<br>
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?<br>
<br>
Jan <br>
<br>
On 28-1-2010 9:20, Thibaut Gheysen wrote:
<blockquote
cite="mid:94e91cde1001280020q34d52013ref97a6317143a882@mail.gmail.com"
type="cite">Hi,<br>
<br>
<span id="result_box" class="long_text"><span
style="background-color: rgb(255, 255, 255);"
title="Le développement du système de coordonnées
Lambert 2005 fait suite à la mise en place du système ETRS89 en Europe.">The
development of the Lambert coordinate system 2005 follows the
introduction of ETRS89 in Europe. </span><span
style="background-color: rgb(255, 255, 255);"
title="De 1989 à 2002,
l'IGN a revu et densifié le réseau géodésique national en utilisant
pleinement le réseau GPS.">From
1989 to 2002, the IGN has reviewed the </span></span><span
id="result_box" class="long_text"><span
style="background-color: rgb(255, 255, 255);"
title="De 1989 à 2002,
l'IGN a revu et densifié le réseau géodésique national en utilisant
pleinement le réseau GPS.">national</span></span><span
id="result_box" class="long_text"><span
style="background-color: rgb(255, 255, 255);"
title="De 1989 à 2002,
l'IGN a revu et densifié le réseau géodésique national en utilisant
pleinement le réseau GPS.">
geodetic network using the GPS network. </span><span
style="background-color: rgb(255, 255, 255);"
title="Ce qui, au final, a
débouché sur le système de projection Lambert 2005.">This
changes has led to the Lambert </span></span><span id="result_box"
class="long_text"><span style="background-color: rgb(255, 255, 255);"
title="Ce qui, au final, a
débouché sur le système de projection Lambert 2005.">2005</span></span><span
id="result_box" class="long_text"><span
style="background-color: rgb(255, 255, 255);"
title="Ce qui, au final, a
débouché sur le système de projection Lambert 2005.">
projection. </span><span style="background-color: rgb(255, 255, 255);"
title="Pour une même
localisation, la différence entre les coordonnées en Lambert 1972 et
Lambert 2005 sont relativement faibles (+/- 1 kilomètre).">For
a given location, the difference between the coordinates in Lambert
1972 and 2005 are relatively low (+ / - 1 kilometer). </span><span
style="background-color: rgb(255, 255, 255);"
title="Vu ce faible écart,
lorsque l'on recevait des données cartographiques en Lambert 2005 sans
que le système de coordonnées utilisé ne soit précisé, on pouvait
croire, si l'on ne faisait pas trop attention, que les données étaient
toujours en Lambert 1972.">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. </span><span
style="background-color: rgb(255, 255, 255);"
title="C'est pourquoi, ils ont ajoutés 500
kilomètres en X et Y (Lambert 2008) : on se rend ainsi compte tout de
suite que le système de projection utilisé n'est plus le 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.</span></span><br>
<br>
Thibaut.<br>
<br>
<br>
<div class="gmail_quote">2010/1/27 Jan Hartmann <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:j.l.h.hartmann@uva.nl">j.l.h.hartmann@uva.nl</a>></span><br>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>
Nice. Our Belgian friends seem to have changed their national<br>
projection. I don't understand this page (Dutch:<br>
<a moz-do-not-send="true" href="http://www.ngi.be/FR/FR4-4.shtm"
target="_blank">http://www.ngi.be/FR/FR4-4.shtm</a>; French:<br>
<a moz-do-not-send="true" href="http://www.ngi.be/FR/FR2-1-7.shtm"
target="_blank">http://www.ngi.be/FR/FR2-1-7.shtm</a>, no English need
apply). It says:<br>
<br>
"Due to the too small deviation (1 kilometer) between the coordinates of<br>
the Lambert 1972 projection and those of the Lambert 2005 projection,<br>
the NGI has changed the parameters of the Lambert 2005 projection, and<br>
created the Lambert 2008 projection".<br>
<br>
What they did was just adding 499.000 to both x and y coordinates of<br>
Lambert 2005.<br>
<br>
Lambert 1972 is the projection as defined in PROJ's epsg file (nr<br>
31370), derived from the EPSG database (coordinate reference nr 411).<br>
Its datum is intl (=Hayford). First standard parallel is 51.166667,<br>
second standard parallel 49.833333, central parallel 90 (?), central<br>
meridian 4.367486666. x_0 = 150000.01256, y_0 = 5400088.4378<br>
<br>
Lambert 2005, as defined on the above page (nothing in the EPSG<br>
database): datum GRS80 (=WGS84, approximately). First standard parallel<br>
51.166667, second standard parallel 49.833333, central parallel<br>
50.7977777, central meridian 4.35916666666. x_0 = 150328, y_0 = 166262<br>
<br>
Lambert 2008 is Lambert 2005 Hi,with 499 km added to both x and y
coordinates<br>
<br>
So, without additional information, I really don't see the relationship<br>
between the 1972, 2005 and 2008 systems. What's the difference between<br>
1972 and 2005, and why did they add 500 km in 2008? Did they change each<br>
and every coordinate on each and every Belgian map in 2005 and are they<br>
changing it again in 2008? Has anyone ever seen a Lambert 2005<br>
coordinate? They are not in the EPSG database.<br>
<br>
If anyone can make sense of this gobbledygook, I would be happy to know.<br>
<br>
Jan<br>
<br>
<br>
<br>
<br>
On 27-1-2010 20:12, OvV_HN wrote:<br>
><br>
> ----- Original Message ----- From: "Jan Hartmann" <<a
moz-do-not-send="true" href="mailto:j.l.h.hartmann@uva.nl">j.l.h.hartmann@uva.nl</a>><br>
> To: "PROJ.4 and general Projections Discussions"<br>
> <<a moz-do-not-send="true" href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</a>><br>
> Cc: "OvV_HN" <<a moz-do-not-send="true"
href="mailto:ovv@hetnet.nl">ovv@hetnet.nl</a>><br>
> Sent: Wednesday, January 27, 2010 7:59 PM<br>
<div class="im">> Subject: Re: [Proj] Belge 1972 / Belgian
Lambert 72 (31370)<br>
> -towgs84parameters<br>
><br>
><br>
</div>
<div class="im">>> Thanks Oscar, good to know. How did you
find this page? Is it<br>
>> reachable from within the ngi site or did you find it with
Google.<br>
>><br>
>> Jan<br>
>><br>
><br>
><br>
</div>
> The path starting from the Dutch language home page is:<br>
> home > know-how > geodetische diensten > Lambert 2008<br>
> <a moz-do-not-send="true" href="http://www.ngi.be/NL/NL2-1-7.shtm"
target="_blank">http://www.ngi.be/NL/NL2-1-7.shtm</a><br>
><br>
> Scroll down to:<br>
> "Relatie tussen de geodetische referentiesystemen van 1972 en 2008"<br>
> ...<br>
> "> uitgebeider schema in pdf"<br>
><br>
> This last link goes to the page I mentioned.<br>
<div>
<div class="h5">><br>
><br>
> Oscar van Vlijmen<br>
><br>
><br>
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