Support xunit in FluxPoints.plot()

[mireianievas]

Using v1.0.1, but I believe it still applies to the development version.

Looking at the code (https://docs.gammapy.org/dev/_modules/gammapy/estimators/points/core.html#FluxPoints.plot ), it looks like like the units in the y-axis are hardcoded in the DEFAULT_UNIT dictionary, but I don't see a reference to the x-axis units. I believe it uses the default units stored in that FluxPoints object.

It would be nice if, similar to how the SpectralModel.plot() work, it could take xunit and yunit as possible parameters and handle the conversions (e.g. TeV -> GeV).

[tunbehaun273]

Add: I would think it is also useful to be able to pass flux_unit as a kwarg to the plot() function again, as it was possible for v0.18.2. This could be done for the FluxPoints but also for the SpectralModels in order to enable easily customizable plots.

[adonath]

@mireianievas Have you checked out the entry "Choose units for plotting" in our how to? (see https://docs.gammapy.org/1.1/user-guide/howto.html)

Removing the unit handling from the Gammapy API was a deliberate decision, because the combination of matpplotlib and Astropy already offers every functionality needed. Here is the copy and paste example from the how to:

import matplotlib.pyplot as plt
from gammapy.estimators import FluxPoints
from astropy import units as u

filename = "$GAMMAPY_DATA/hawc_crab/HAWC19_flux_points.fits"
fp = FluxPoints.read(filename)

ax = plt.subplot()
ax.xaxis.set_units(u.eV)
ax.yaxis.set_units(u.Unit("erg cm-2 s-1"))
fp.plot(ax=ax, sed_type="e2dnde")

The ax.xaxis.set_units(u.eV) and ax.yaxis.set_units(u.eV) pattern works with every(!) plot in Gammapy. Two things are important:

• You have to create an independent plot axis first using e.g. plt.subplot()
• The units have to be set before plotting, such that the plotted quantities can be converted to the right units