[PROJ] cs2cs and +towgs84

[Kristian Evers]

Stefano,

cs2cs uses the ”best guestimate” operation between source and destination CRS.
If you want something else you need to specify that yourself. projinfo can help you
find the correct transformation:

$ projinfo -k operation -o PROJ EPSG:1660
PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=push +v_3 +step +proj=cart +ellps=intl +step +proj=helmert +x=-104.1 +y=-49.1 +z=-9.9 +rx=0.971 +ry=-2.917 +rz=0.714 +s=-11.68 +convention=position_vector +step +inv +proj=cart +ellps=WGS84 +step +proj=pop +v_3 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1

Which you can then use with cct:

$ echo 41.7447031 15.0618939 | cct -z0 -t0 -d8 +proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=push +v_3 +step +proj=cart +ellps=intl +step +proj=helmert +x=-104.1 +y=-49.1 +z=-9.9 +rx=0.971 +ry=-2.917 +rz=0.714 +s=-11.68 +convention=position_vector +step +inv +proj=cart +ellps=WGS84 +step +proj=pop +v_3 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1
  41.74535412    15.06180323    0.00000000        0.0000

That should do the trick :-)

Please don’t use the +towgs84 parameter – it is deprecated and only supported for legacy reasons.

/Kristian

From: PROJ <proj-bounces at lists.osgeo.org> On Behalf Of Stefano Iacovella
Sent: 5. februar 2020 13:57
To: proj at lists.osgeo.org
Subject: [PROJ] cs2cs and +towgs84

Hello,

I already read the cs2cs usage page at [1] but I am still a little bit confused about the +towgs84 option so I am looking for your help.

I am trying to convert from EPSG:4265 CRS to EPSG:4326 CRS

First of all I used the following syntax

$> cs2cs -d 8 epsg:4265 epsg:4326
41.7447031 15.0618939
41.74535412     15.06180323 0.00000000

this way the coordinate are transformed but I have no control on which operation is really used, e.g. I don't know which are the towgs84's parameters

Really I want to use the EPSG:1660 operation, so I tried to add the +towgs84 option but I got an error:

$> cs2cs -d 8 epsg:4265 epsg:4326 +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
proj_create: crs not found
Rel. 6.3.0, January 1st, 2020
<cs2cs>:
cannot instantiate source coordinate system
program abnormally terminated

Which is the correct syntax to be used?

Thank you in advance

Stefano

[1] https://proj.org/apps/cs2cs.html
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