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<p>Nicolas,</p>
<p>I believe the Helmert transformation is used when using IGNF
codes, because the IGNF database has only recorded the use of the
ntf_r93 grid for NTF to RGF93, but not for NTF to ETRS89 (by the
way, just reiterating that IGN is more than welcome to take over
on maintenance & updates of the IGNF part of the PROJ
database). And when transforming between 2 IGNF codes, PROJ by
default will only consider transformations in the IGNF domain. But
if you use EPSG codes, then ntf_r93 is available to transforme
between NTF and ETRS89.</p>
<p>To get a vertical transformation, you also need to use 3D CRS.<br>
</p>
<p>For example<br>
</p>
<p>projinfo -s "NTF geographiques Paris (gr) + NGF-IGN69 height" -t
IGNF:ETRS89LCC --3d --spatial-test intersects <br>
</p>
<p>reports the following pipeline:<br>
</p>
<p>unknown id, axis order change (2D) + NTF (Paris) to NTF (1) + NTF
to RGF93 v1 (1) + Inverse of RGF93 v1 to NGF-IGN69 height (1) +
RGF93 v1 to ETRS89 (1) + axis order change (geographic3D
horizontal) + ETRS89 LAMBERT CONFORMAL CONIC, 1.6 m, France -
mainland onshore., at least one grid missing<br>
<br>
PROJ string:<br>
+proj=pipeline<br>
+step +proj=unitconvert +xy_in=grad +xy_out=rad<br>
+step +inv +proj=longlat +ellps=clrk80ign +pm=paris<br>
+step +proj=push +v_3<br>
+step +proj=cart +ellps=clrk80ign<br>
+step +proj=xyzgridshift +grids=fr_ign_gr3df97a.tif
+grid_ref=output_crs<br>
+ellps=GRS80<br>
+step +inv +proj=cart +ellps=GRS80<br>
+step +proj=pop +v_3<br>
+step +proj=vgridshift +grids=fr_ign_RAF18.tif +multiplier=1<br>
+step +proj=lcc +lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65
+x_0=4000000<br>
+y_0=2800000 +ellps=GRS80<br>
</p>
<p><br>
</p>
<p>Here, as there's a mix of objects from different authorities
(IGNF and EPSG), then EPSG transformations are considered, hence
you get the gr3df97a grid.<br>
</p>
<p>$ echo 0 56.000000 0 | PROJ_NETWORK=ON bin/cs2cs -d 3 "NTF
geographiques Paris (gr) + NGF-IGN69 height" IGNF:ETRS89LCC --3d <br>
3474789.997 2655359.291 43.644</p>
<p>which is the application of the above pipeline:<br>
</p>
<p>$ echo 0 56.000000 0 | PROJ_NETWORK=ON bin/cct -d 3
+proj=pipeline +step +proj=unitconvert +xy_in=grad +xy_out=rad
+step +inv +proj=longlat +ellps=clrk80ign +pm=paris +step
+proj=push +v_3 +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=pop
+v_3 +step +proj=vgridshift +grids=fr_ign_RAF18.tif +multiplier=1
+step +proj=lcc +lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65
+x_0=4000000 +y_0=2800000 +ellps=GRS80<br>
<br>
</p>
<p>If you want to get exactly the below pipeline, you'll have to
tweak proj.db to create a compound CRS for "NTF geographiques
Paris (gr) + NGF-IGN69 height", and then create a custom record in
other_transformation for the transformation between this compound
CRS and (a 3D projected CRS derived from) IGNF:ETRS89LCC. Cf
data/sql/other_transformation_custom.sql for potential inspiration</p>
<p>Even<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">Le 15/02/2024 à 19:46, Nicolas
Bellaiche via PROJ a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:613751832.7612339.1708022783849.JavaMail.zimbra@ign.fr">
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<div>Hi there,</div>
<div><br data-mce-bogus="1">
</div>
<div>I try to make a conversion using shiftgrids from IGNF: NTFP
to IGNF:ETRS89LCC. By default, it seems that it uses the
helmert approximation between the 2 crs and i cannot figure
out how to use the grid fr_ign_ntf_r93.</div>
<div><br data-mce-bogus="1">
</div>
<div>So far i've found how to create a pipeline that works with
cct, but i'd like to have a code that represents the crs and
be able to go to different destination crs with the cs2cs
application. Any idea?</div>
<div><br data-mce-bogus="1">
</div>
<div><span
style="color: #5d6c79; font-family: Menlo; font-size: 15px; font-style: normal; font-variant-ligatures: no-common-ligatures; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: #ffffff; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;"
data-mce-style="color: #5d6c79; font-family: Menlo; font-size: 15px; font-style: normal; font-variant-ligatures: no-common-ligatures; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: #ffffff; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">(helmert
approx + no geoid with the standard codes)</span></div>
<div>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1">echo 0 56<span
class="Apple-converted-space"> </span>0 | ./cs2cs<span
class="Apple-converted-space"> </span>+ from IGNF:NTFP<span
class="Apple-converted-space"> </span>+to
IGNF:ETRS89LCC </span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1">result : </span><span
class="s1">3474788.21<span class="Apple-tab-span"> </span>2655358.23
0.00</span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1"></span><br>
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1">(correct
pipeline)</span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1">echo 0
56.000000 0 | PROJ_DEBUG=3 ./cct +proj=pipeline +step
+proj=unitconvert +xy_in=grad +xy_out=rad +step +inv
+proj=longlat +ellps=clrk80ign +pm=paris +step
+proj=hgridshift +grids=fr_ign_ntf_r93.tif +step +inv
+proj=vgridshift +grids=RAF09.gtx +step +proj=lcc
+lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65 +x_0=4000000
+y_0=2800000 +ellps=GRS80</span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1"></span><br>
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1"><span
class="Apple-converted-space">result : </span>3474789.9972
<span class="Apple-converted-space"> </span>2655359.2908
<span class="Apple-converted-space"> </span>43.6421
<span class="Apple-converted-space"> </span>inf</span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1"></span><br>
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><span class="s1">reference
from THE official IGN/SGN dataset:</span></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;">3474789.997<span
class="Apple-tab-span"> </span>2655359.291<span
class="Apple-tab-span"> </span>43.642</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><br>
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><br data-mce-bogus="1">
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><font
face="arial, helvetica, sans-serif" color="#000000"><span
style="font-size: 16px;">Thanks a lot for your help,</span></font></p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><br data-mce-bogus="1">
</p>
<p class="p1" style="margin: 0px;"
data-mce-style="margin: 0px;"><font
face="arial, helvetica, sans-serif" color="#000000"><span
style="font-size: 16px;">Nicolas Bellaiche</span></font></p>
<div style="clear: both;" data-mce-style="clear: both;"><br>
</div>
</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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</blockquote>
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