Wrong coordinates of events when producing a counts map

Gammapy version 0.20.dev726+g57be15f25

Bug description When producing a counts map, the coordinates of the events seem to be shifted to the source position (current master branch):

Expected behavior Background counts are expected to peak at the pointing positions (which is the case for gammapy 0.19):

To Reproduce

from gammapy.data import DataStore
from gammapy import __version__
import numpy as np
from astropy.coordinates.angle_utilities import angular_separation
import astropy.units as u
from astropy.coordinates import SkyCoord
from gammapy.makers import MapDatasetMaker
from gammapy.datasets import MapDataset, Datasets
from gammapy.maps import MapAxis, WcsGeom
import matplotlib.pyplot as plt

data_store = DataStore.from_dir(".")
observations = data_store.get_observations(required_irf=['aeff', 'edisp'])

ra_pnt = [obs.events.table.meta['RA_PNT'] for obs in observations] * u.deg
dec_pnt = [obs.events.table.meta['DEC_PNT'] for obs in observations] * u.deg
ra_obj = [obs.events.table.meta['RA_OBJ'] for obs in observations] * u.deg
dec_obj = [obs.events.table.meta['DEC_OBJ'] for obs in observations] * u.deg

separation = angular_separation(ra_pnt, dec_pnt, ra_obj, dec_obj)
mask = np.abs(separation - 1.8 * u.deg) < 0.05 * u.deg
observations18deg = data_store.get_observations(data_store.obs_table['OBS_ID'][mask], required_irf=["aeff", "edisp"])

source_pos = SkyCoord.from_name("Crab")

e_reco = MapAxis.from_energy_bounds(0.07, 2, 1, unit="TeV", name="energy")
geom = WcsGeom.create(skydir=source_pos, axes=[e_reco], width=4, binsz=0.1)
maker = MapDatasetMaker(selection=["counts"]) 

datasets = []

for obs in observations18deg:
    dataset = MapDataset.create(geom, name=str(obs.obs_id))
    dataset = maker.run(dataset, obs)
    datasets.append(dataset)
    
datasets = Datasets(datasets)
plt.figure()
counts = datasets.stack_reduce().counts.plot(add_cbar=True)
plt.tight_layout()
plt.savefig(f"counts_gammapy_{__version__}.png", dpi=300, bbox_inches='tight')

[SimoneMender]

@adonath I just made a test with the “$GAMMAPY_DATA/cta-1dc/index/gps” dataset. In this case, it looks good. So probably there is a problem with my dataset and in the different gammapy branches, there is only a difference from where some information is read.

Current master branch (0.20.dev726+g57be15f25):

0.19:

from gammapy.data import DataStore
from gammapy import __version__
import numpy as np
from astropy.coordinates.angle_utilities import angular_separation
import astropy.units as u
from astropy.coordinates import SkyCoord
from gammapy.makers import MapDatasetMaker
from gammapy.datasets import MapDataset, Datasets
from gammapy.maps import MapAxis, WcsGeom
import matplotlib.pyplot as plt

data_store = DataStore.from_dir("$GAMMAPY_DATA/cta-1dc/index/gps")
obs_id = [110380, 111140, 111159]
observations = data_store.get_observations(obs_id)

axis = MapAxis.from_edges(
    np.logspace(-1.0, 1.0, 2), unit="TeV", name="energy", interp="log"
)
e_reco = MapAxis.from_energy_bounds(0.07, 2, 1, unit="TeV", name="energy")
source_pos = SkyCoord.from_name("Galactic Center")
geom = WcsGeom.create(skydir=source_pos, axes=[e_reco], width=4, binsz=0.1)
maker = MapDatasetMaker(selection=["counts"]) 

datasets = []

for obs in observations:
    dataset = MapDataset.create(geom, name=str(obs.obs_id))
    dataset = maker.run(dataset, obs)
    datasets.append(dataset)
    
    
datasets = Datasets(datasets)
plt.figure()
counts = datasets.stack_reduce().counts.plot(add_cbar=True)
plt.tight_layout()
plt.savefig(f"counts_gammapy_hess_{__version__}.png", dpi=300, bbox_inches='tight')

[maxnoe]

The reason was a wrong assumption about the observation order, leading to the wrong observations being selected. See #3891