@Nicolas
I get the same result as you, if the nadgrid and geoidgrid files are not
selected.
Maybe, in your system, cs2cs does not know where to find grid files. So
maybe setting this, or copying the grid files in the actual directory
can help.
You can check it with:
echo 0 56.000000 0 | ./cs2cs -f "%.3f" +proj=eqc
+R=6366197.72367581 +to_meter=100000 +lon_0=-2.3372291667E
+nadgrids=@null +geoidgrids=@null +to +proj=lcc
+lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65 +x_0=4000000 +y_0=2800000
+ellps=GRS80
That produces the same wrong result that you got, because no grid files
are selected.
Please let me know, if it works! Thank you!
Gabor
On 2024-02-20 14:41, Nicolas Bellaiche wrote:
@Gabor
your pipeline gives me this result with Proj-9.3.1:
echo 0 56.000000 0 | ./cs2cs -f "%.3f" +proj=eqc
+R=6366197.72367581 +to_meter=100000 +lon_0=-2.3372291667E
+nadgrids=fr_ign_ntf_r93.tif +geoidgrids=RAF09.gtx +to +proj=lcc
+lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65 +x_0=4000000 +y_0=2800000
+ellps=GRS80
3474840.045 2655360.932 0.000
@Even
I'm studying this, hopefully I find how it works without sweating too
much!
Nicolas
----- Mail original -----
De: "molnar via PROJ" <[email protected]>
À: "proj" <[email protected]>
Envoyé: Lundi 19 Février 2024 21:15:54
Objet: Re: [PROJ] Help needed for a cs2cs pipeline with shift grids
Dear Nicolas,
If you really need a cs2cs string, that converts from grad to Lambert
projection, here it is:
cs2cs -f "%.3f" +proj=eqc +R=6366197.72367581 +to_meter=100000
+lon_0=-2.3372291667E +nadgrids=fr_ign_ntf_r93.tif
+geoidgrids=RAF09.gtx
+to +proj=lcc +lat_0=52 +lon_0=10 +lat_1=35 +lat_2=65 +x_0=4000000
+y_0=2800000 +ellps=GRS80
This produces exactly the same result as your cct code!
It simulates the grad to degree transformation with an equidistant
cylindrical projection. (My favorite trick :-)) Input data (that is in
grad) handled internally as meter, and the first part of the cs2cs
command with equidistant cylindrical projection converts it to degree.
As a surprise for me, nadgrids and geoidgrids should be applied before
the +to switch.
Best wishes,
Gabor
On 2024-02-18 14:16, Even Rouault via PROJ wrote:
Nicolas,
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.
To get a vertical transformation, you also need to use 3D CRS.
For example
projinfo -s "NTF geographiques Paris (gr) + NGF-IGN69 height" -t
IGNF:ETRS89LCC --3d --spatial-test intersects
reports the following pipeline:
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
PROJ string:
+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
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.
$ echo 0 56.000000 0 | PROJ_NETWORK=ON bin/cs2cs -d 3 "NTF
geographiques Paris (gr) + NGF-IGN69 height" IGNF:ETRS89LCC --3d
3474789.997 2655359.291 43.644
which is the application of the above pipeline:
$ 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
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
Even
Le 15/02/2024 à 19:46, Nicolas Bellaiche via PROJ a écrit :
Hi there,
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.
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?
(helmert approx + no geoid with the standard codes)
echo 0 56 0 | ./cs2cs + from IGNF:NTFP +to IGNF:ETRS89LCC
result : 3474788.21 2655358.23 0.00
(correct pipeline)
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
result : 3474789.9972 2655359.2908 43.6421 inf
reference from THE official IGN/SGN dataset:
3474789.997 2655359.291 43.642
Thanks a lot for your help,
Nicolas Bellaiche
_______________________________________________
PROJ mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/proj
--
http://www.spatialys.com
My software is free, but my time generally not.
_______________________________________________
PROJ mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/proj
_______________________________________________
PROJ mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/proj
_______________________________________________
PROJ mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/proj
