Detection Overlays

To aid the matching of positional data, image queries support detection overlays.

Note

By default, detection overlays are configured for the following Vizier catalogues:

• Gaia - gaia

• Pan-STARRS - panstarrs

• SkyMapper - skymapper

• GALEX - galex

• ROSAT - rosat

• SDSS - sdss

• WISE - wise

• 2MASS - 2mass

• eROSITA - erosita

A tutorial on defining detection overlays for any Vizier catalogue can be found here.

Requesting an Overlay

An overlay can be requested by passing overlays to query() with a list of surveys:

from ATK import query

ps_query = query("image", targets=2552928187080872832, survey="panstarrs", band="g", size=120, overlays=["galex"], path="example_image_2.fits.gz")
ps_query.open()

As with all figure elements, overlayed detections can be hidden by clicking them in the legend. Hovering over a detection displays its key parameters (e.g. its position and magnitude), and clicking a detection searches for the object in SIMBAD.

Detections are corrected for proper motion where possible, as stated by the corrected flag. Non-gaia detections are also corrected by crossmatching them with corresponding Gaia detections. The GALEX data that was found for van Maanen’s Star from the previous section is a match!

Overlay Configuration

By default, a detection overlay uses whichever band is listed first in the catalogue’s overlay definition (see here). If a different band is required, or perhaps multiple bands from the same catalogue need to be overlayed simultaneously, overlays can instead be passed as a dict:

ps_query = query(
    "image",
    targets=2552928187080872832,
    survey="panstarrs",
    band="g",
    size=120,
    overlays={"galex": ["NUVmag", "FUVmag"]},
    path="example_image_4.fits.gz",
)
ps_query.open()

Note

Where possible, detection markers are scaled in size by magnitude. Markers labelled galex detection in the above image are detections that had an invalid magnitude, and hence could not be scaled.

Download this Tutorial