<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>I confirm that my issue was linked to an old IGNF file coming from PROJ4. </div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><b>De: </b>"Nicolas Bellaiche" <nicolas.bellaiche@ign.fr><br><b>À: </b>"Even Rouault" <even.rouault@spatialys.com><br><b>Cc: </b>"proj" <PROJ@lists.osgeo.org><br><b>Envoyé: </b>Vendredi 2 Juin 2023 11:14:39<br><b>Objet: </b>Re: [PROJ] PROJ 9 & old syntax +init=<br></div><div><br></div><div data-marker="__QUOTED_TEXT__"><div style="font-family:'arial' , 'helvetica' , sans-serif;font-size:12pt;color:#000000"><br><div><span style="text-decoration:underline" class=""></span><p style="margin:0px"><span style="color:rgb( 0 , 0 , 255 )">1) OK, I found out that the definition in the dataset file includes a conversion from altitude to ellipsoid height which explains the difference.</span></p><p style="margin:0px">2) This is very possible that I have an old IGNF file from PROJ4. I will check that now. Thanks for the clue, I didn't know there was an update on this file.</p><blockquote><div style="color:#000000;font-family:'arial' , 'helvetica' , sans-serif;font-size:12pt;font-style:normal;font-weight:normal;letter-spacing:normal;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration:none"><div><div class=""><div class=""><div><blockquote class=""><div class=""><div class=""><div class="" style="font-family:'arial' , 'helvetica' , sans-serif;font-size:12pt"><div class=""><div class="" style="font-family:'arial' , 'helvetica' , sans-serif;font-size:12pt"><br></div></div></div></div></div></blockquote></div></div></div></div></div></blockquote><br class="">
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1.a) NEW SYNTAX: z not correct (grid shift
not used)</div>
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<span style="font-size:8pt" class=""><strong class=""> echo 600000.00000000
300097.53400000 0.00000000 |
./bin/cs2cs IGNF:LAMB1 +to
IGNF:UTM31RGF93</strong></span><br class="">
<span style="font-size:8pt" class="">452845.19 5583309.40
0.00</span><br class="">
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Which grid shift file are you refering to ? ntf_r93.gsb ? I assume.
But this is a horizontal datum shift. No vertical correction. This
horizontal shift is applied, otherwise you'd get "452843.46
5583308.13 0.00" as a result<br>
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<span style="font-family:'arial' , 'helvetica' , sans-serif;font-size:16px;font-style:normal;font-weight:normal;letter-spacing:normal;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb( 255 , 255 , 255 );text-decoration:none;float:none;display:inline !important" class="">1.b) OLD SYNTAX: z
correct:</span></div>
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<span style="font-size:8pt" class=""><strong class="">echo 600000.00000000
300097.53400000 0.00000000 |
./bin/cs2cs +init=IGNF:LAMB1 +to
+init=IGNF:UTM31RGF93</strong></span><br class="">
<span style="font-size:8pt" class="">452845.19 5583309.40
43.64</span><br class="">
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<p>I have no idea how you get this result. You should really try
stopping using the (old) IGNF file with newer PROJ. This is mostly
in unsupported land. Even when trying, with both PROJ 5.2 and
latest PROJ master, and with the IGNF file supplied with PROJ 5.2,
I still get the "452845.19 5583309.40 0.00" result. Did you tweak
your IGNF file ?</p>
<p>The only way I can get something close to what you get is by
composing a manual pipeline using the gr3df97a grid with:<br>
</p>
<p>echo 600000.00000000 300097.53400000 0.00000000 |
PROJ_NETWORK=ON PROJ_DEBUG=3 bin/cct +proj=pipeline +step +inv
+proj=lcc +lat_1=49.5 +lat_0=49.5 +lon_0=0 +k_0=0.99987734
+x_0=600000 +y_0=200000 +a=6378249.2 +rf=293.466021 +pm=paris
+step +proj=cart +ellps=clrk80ign +step +proj=xyzgridshift
+grids=fr_ign_gr3df97a.tif +grid_ref=output_crs +ellps=GRS80 +step
+inv +proj=cart +ellps=GRS80 +step +proj=utm +zone=31
+ellps=GRS80<br>
452845.1911 5583309.3959 42.9892 inf<br>
</p>
<p>But it seems a bit dubious to have a Z correction term for NTF
<--> RGF93. And newer PROJ when operating with 2D CRS
doesn't change the Z value. You may sometimes upgrade your CRS to
3D by adding the --3d switch to cs2cs or projinfo, but if the
transformations available are only 2D ones, that won't make
miracles.<br>
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<p>What does Circe does under the hood for that transformation?<br>
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<span style="text-decoration:underline" class="">2) Example where the old syntax
gives a wrong result while the new
syntax works:</span></div>
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<div class="">2.a) OLD SYNTAX from
cartographic to geocentric coordinates /
result is wrong</div>
<div class=""><br class="">
<span style="font-size:8pt" class=""><strong class="">echo 652760.737 7033791.243
43.642 | PROJ_DEBUG=3 ./bin/cs2cs
+init=IGNF:LAMB93 +to +init=IGNF:RGF93</strong></span></div>
<div class=""><span style="font-size:8pt;font-family:'new roman' 'new york' 'times' serif" class="">4070355.05 166080.07
4891332.24</span></div>
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<p>I do get "4070327.25<span class="Apple-tab-span" style="white-space:pre"> </span>166078.93
4891298.61". This really smells like your IGNF file isn't the one
of PROJ 5.2<br>
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<div class=""><span style="font-family:'arial' , 'helvetica' , sans-serif;font-size:16px;font-style:normal;font-weight:normal;letter-spacing:normal;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb( 255 , 255 , 255 );text-decoration:none;float:none;display:inline !important" class="">2.b) NEW SYNTAX
from cartographic to geocentric
coordinates / result is correct</span><br class="">
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<div style="margin:0px;font-style:normal;font-weight:normal;font-stretch:normal;font-size:11px;line-height:normal;font-family:'menlo'" class=""><strong class="">echo
652760.737 7033791.243 43.642 |
PROJ_DEBUG=3 ./bin/cs2cs IGNF:LAMB93
+to IGNF:RGF93<span class="Apple-converted-space"> </span></strong></div>
<div style="margin:0px;font-style:normal;font-weight:normal;font-stretch:normal;font-size:11px;line-height:normal;font-family:'menlo'" class="">4070327.25<span class="Apple-tab-span" style="white-space:pre"> </span>166078.93
4891298.61</div>
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