plotting `ConstantSpatialModel`

Models.plot_regions()/plot_positions() fails if it contains any ConstantSpatialModel (or ConstantFluxSpatialModel), with a rather complicated error message. I suppose this is because there is no position defined for these models.

It would be nice to have this fixed before the 1.0rc release.

A quick solution can be to simply add an exception for ValueError as well here https://github.com/gammapy/gammapy/blob/a68be851d6523742627ed293aa1122c795680f8e/gammapy/modeling/models/core.py#L918.

[adonath]

For compatibility with regions 0.6 we have to remove the np.nan values anyway. So I’ll do the compatibility update with regions 0.6 and the we see whether the plotting issue remains…

[adonath]

OK

from gammapy.maps import Map
from gammapy.modeling.models import (
    SkyModel,
    PowerLawSpectralModel,
    ConstantSpatialModel,
    PointSpatialModel,
    GaussianSpatialModel,
    Models
)

m1 = SkyModel(
    spectral_model=PowerLawSpectralModel(),
    spatial_model=ConstantSpatialModel()
)

m2 = SkyModel(
    spectral_model=PowerLawSpectralModel(),
    spatial_model=PointSpatialModel()
)

models = Models([m1, m2])

m = Map.create(width=10)
ax = m.plot()
models.plot_regions(ax=ax);

Triggers:

ValueError: need at least one array to concatenate

Which is raised from matplotlib…