Reproducing SWEREF99 to ITRF2014 Transformation using proj.org cct

Question

The Swedish Geodetic Agency Lantmateriet provides a document (see references) with a procedure for transforming coordinates between ITRF2014 and SWEREF99. The document also provides and example of the transformation.

I am attempting to perform the transformation using cct from proj.org since the document alludes to it being the documented method of doing so. There is a partial example of using it here, but it does not include a change of epoch.

In the document, there is an example transform in geocentric coordinates:

Initial ITRF2014 coordinates (epoch 2020.25) of the example stations
2251700.0000 819600.0000 5891200.0000

The coordinates of the example stations in SWEREF 99 (epoch 1999.5).
2251700.5587 819599.6862 5891199.6467

How do I reproduce these results using proj.org?

The previously mentioned method was:

echo  2251700.0000 819600.0000 5891200.0000 2020.25 | cct NKG:ITRF2014_TO_SE

Which emits coordinates for the same epoch (2020.25):

 2251700.5587    819599.6862  5891199.6467     2020.2500

How does one change the epoch to 1999.5 to match SWEREF99 example?

Adding the +t_epoch=1999.5 does not seem to help.

dusha@computer:~$ echo  3468700.0000 864800.0000 5264500.0000 2020.25 | cct  +t_epoch=1999.5 NKG:ITRF2014_TO_SE
proj_create: unrecognized format / unknown name
cct: Bad transformation arguments - (Invalid PROJ string syntax)
    'cct -h' for help

I am running a recent release from Debian:

dusha@computer:~$ cct --version
cct: Rel. 9.1.0, September 1st, 2022

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References:

• Lantmateriet, "Transformation between ITRF 2014/WGS 84 and SWEREF 99", 2021-03-12.

Answer 1

the transformation is correct but I agree that it can be confusing with the output epoch.

SWEREF 99 is a static reference frame, so the coordinates are not supposed to change with the epoch, i.e. the epoch does not matter as long as you do not have local movements. IF you have a local movemnet (e.g. land slide) it would make sense to mark the coordinates with the observation epoch, in this case 2020.25.

The epoch 1999.5 is in the definition of the SWEREF 99 frame (epoch with respect to the land uplift). Further on SWEREF 99 is a realization of the European reference system ETRS89, with the reference epoch 1989.0 (with respect to the plate techtonics). Both those epochs are included and taken care of in the NKG:ITRF2014_TO_SE-transformation.

To conclude: With a static frame you can interpret the epoch as the observation epoch. Normally the epoch of the coordinates does not matter in a static frame.

Best Regards, Lotti Jivall, Lantmäteriet, Sweden