Mapping to/from rho tor norm

[AreWeDreaming]

Leaf of #258
Adds rho_tor_norm to the magnetic coordinates omas_physics.remap_flux_coordinates can map between. Wouldn't hurt if this someone double checked my math once #258 is merged. I did do a spot check and while the result wasn't perfect it was not too far off.
Arguably a unit test wouldn't hurt here, but I don't have time to write it at the moment.

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[torrinba]

I see no new changes here, but if you can point me to where the rho_tor_norm conversion was added I'm happy to look it over

[AreWeDreaming]

omas/omas/omas_physics.py

Line 390 in 6f2afab

def remap_flux_coordinates(ods, time_index, origin, destination, values):

and above

[torrinba]

Is this comment still accurate? It appears not to be...

def remap_flux_coordinates(ods, time_index, origin, destination, values):
    """
    Maps from one magnetic coordinate system to another. At the moment only supports
    psi <-> rho_pol

[torrinba]

Have you tested whether the transformations to/from phi are correct? If it isn't already in the ODS, I have some concerns about this working correctly, without accounting for the boundary terms

phi_spline = q_spline.antiderivative(1)

Of course the magnitude of phi doesn't matter if you're just interested in rho_tor_norm, but it could help avoid some of the concerns you've addressed with the wrong_sign_mask

[torrinba]

omas/omas/omas_physics.py

Line 313 in 6f2afab

phi_grid = ods["equilibrium"]["time_slice"][time_index]["profiles_1d"]["phi"][psi_mask]

This line assumes that the data already exists, which might not be the case if the conversion is from rho_tor_norm. It would be more robust to protect against the ValueError in this case by falling back on add_phi_to_equilbrium_profiles_1d_ods as well

[torrinba]

phi_spl = InterpolatedUnivariateSpline(psi_grid[psi_grid_mask]

Assumes that psi is strictly increasing (AFAIK this is a requirement for InterpolatedUnivariateSpline), but the sign of psi depends on the COCOs so I don't think this is a safe assumption.