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Hello Eric<br>
<br>
Le 08/05/12 08:30, Eric HORLAIT a écrit :
<blockquote cite="mid:CBCDDA04.4F248%25ehorlait@tutor.fr"
type="cite">
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<div style="font-size: medium; font-weight: normal;
font-family: Helvetica; "><font
face="Calibri,Verdana,Helvetica,Arial"><span
style="font-size: 11pt; ">I did quite that with Gtools
with the following code. The test is a comparaion with
cs2cs result. And It does not match!</span></font></div>
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<div style="font-size: medium; font-weight: normal; font-family:
Helvetica; "><font face="Calibri,Verdana,Helvetica,Arial"><span
style="font-size: 11pt; ">Do you think this will be the same
thing with GToolKit?</span></font></div>
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<br>
I tested and Geotk produces the same result than Geotools. It took
me a little while to investigate, and finally the problem appears to
be in the WKT string. The IGN:LAMBE definition is (trimming the
parts not relevant to this discussion):<br>
<br>
PROJCS["Lambert II étendu", GEOGCS[..., PRIMEM["Paris",
2.337229167], UNIT["grad", 0.01570796326794897],
...],PROJECTION["Lambert_Conformal_Conic_1SP"], ...
PARAMETER["latitude_of_origin",46.8], ...]<br>
<br>
The key element is UNIT["grad", ...]. According the WKT
specification, this implies that the PRIMEM element and all
PARAMETER elements having angular values shall be in gradiants.
However many software are not compliant with this WKT clause,
including Proj.4/GDAL and ESRI. The IGN definition string follows
that path: the PRIMEM value is 2.337°, which is decimal degrees (the
values in gradiants is 2.597), and the latitude of origin is in
degrees too (46.8°, while the value in gradiants according the EPSG
database is 52).<br>
<br>
However Geotk tries to be strictly OGC compliant and interprets the
2.337 and 46.8 angle values as gradiants, because of the
UNIT["grad"] declaration. It was apparently not the intend of IGN.
If you replace UNIT[\"grad\",0.01570796326794897] by
UNIT[\"degree\",0.0174532925199433] in the WKT definition, you
should get the same result than cs2cs.<br>
<br>
Geotk tries to handle the "various WKT flavors" problem with a
Convention enumeration:<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.geotoolkit.org/apidocs/org/geotoolkit/io/wkt/Convention.html">http://www.geotoolkit.org/apidocs/org/geotoolkit/io/wkt/Convention.html</a><br>
<br>
The convention you are facing is the "ESRI" convention. Current
Geotk implementation applies the conventions only at formatting time
and, in the ESRI convention case, only to PRIMEM value. However
given the issue you reported, I would bet that ESRI uses decimal
degrees not only for PRIMEM, but also for all PARAMETER angular
values. I will update the code in order to extend the ESRI case
handling to PARAMETER elements as well, and to parsing too.<br>
<br>
Regards,<br>
<br>
Martin<br>
<br>
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