YAC coupling: Make projection user-configurable

[BenjaminRodenberg]

The projection "EPSG:3413" is currently hard-coded:

elmerfem/fem/src/project_to_lonlat.c

Lines 42 to 44 in df4bd30

	PJ * P =
	proj_create_crs_to_crs(
	PJ_DEFAULT_CTX, "EPSG:3413", "+proj=longlat +datum=WGS84", NULL);

We need to support arbitrary projections. Therefore, this should be exposed to the user and configurable (via the .sif file).

@tzwinger hope this summarizes our discussion and the goal sufficiently? I can take care of this.

[fgillet]

Hi;

I wrote a module under elmerice/Utils/ProjUtils.F90 that contains utility subroutines for geographical transformations;

It is used by the XIOSOutputSolver.F90 and I also wrote user functions under UserFunctions/USF_proj.F90;
see the test case under elmerice/Tests/Proj_South/

I have hard coded polar stereographic projection but also added the support for the fortrangis libraries https://fortrangis.sourceforge.net/ which itself has a support for the proj library to support arbitrary projections.

The projection is defined in the Simulation section of the .sif

Maybe your can use/update this?

Fabien

[fgillet]

BTW I fixed the compilation of USF_proj.F90 in the Cmake configuration in the elmerice branch last month:
b917316

[BenjaminRodenberg]

Thanks for the reminder @fgillet ! I already created a first prototype before I saw your comment here. But I looked at the code you are pointing to. I have to check with my colleagues but I think it provides everything we need. If I get it right it allows to use EPSG:3413 - the one we were already using before - and EPSG:3031 - the counterpart for the southern hemisphere. It's also nice that there are some tests for the code.

#783 contains my prototype for this feature. I will potentially replace the implementation with code from elmerice/Utils/ProjUtils.F90 in a second step.

[fgillet]

Hi @BenjaminRodenberg;
Yes, I have coded the polarstereographic projections; and the latitude of true scale and central meridian are set by the user;
so EPSG 3031 (Antarctic) is

  projection type = String "polar stereographic south"
  central_meridian = Real 0.0
  latitude_of_origin = Real -71.0

and EPSG 3413 (Greenland):

  projection type = String "polar stereographic north"
  central_meridian = Real -45.0
  latitude_of_origin = Real 70.0

And using the fortrangis interface to proj allows to use any projection; e.g. UTM for glaciers.