Viewing LSST Source Detection Footprints

The Firefly backend for lsst.afw.display includes specialized functions for overlaying and interacting with LSST Source Detection Footprints.

Here is an example using HSC-reprocessed data. When using the LSST Science Platform, a “medium” or larger container size is recommended.

Define a Butler instance and an identifier for retrieving the data.

from lsst.daf.butler import Butler
butler = Butler('/datasets/hsc/repo/', collections='rerun/RC/w_2019_22/DM-19244/')
dataId = dict(pysical_filter='HSC-R', tract=9813, patch=32)

Define bounding boxes for two regions of interest, one for the catalog and a somewhat larger one for the image. Use these to retrieve a cutout of the coadd image.

import lsst.geom as geom
footprintsBbox = geom.Box2I(corner=geom.Point2I(16900, 18700),
                            dimensions=geom.Extent2I(600,600))
imageBbox = geom.Box2I(corner=geom.Point2I(16800, 18600),
                       dimensions=geom.Extent2I(800,800))
calexp = butler.get('deepCoadd_calexp', dataId=dataId, parameters={'bbox'=imageBbox})

Retrieve the entire catalog and then select only those records with pixel locations inside the footprints bounding box.

measCat = butler.get('deepCoadd_meas', dataId=dataId)
import numpy as np
catSelect = np.array([footprintsBbox.contains(geom.Point2I(r.getX(), r.getY()))
                   for r in measCat])
catalogSubset = measCat.subset(catSelect)

Set up the Firefly display and display the image.

import lsst.afw.display as afwDisplay
display1 = afwDisplay.Display(frame=1, backend='firefly')
display1.setMaskTransparency(80)
display1.scale('asinh', 10, 80, unit='percent', Q=6)
display1.resetLayout()
display1.mtv(calexp)

Overlay the footprints and show the accompanying table. Colors can be specified as a name like “cyan” or “afwDisplay.RED”; as an rgb value such as “rgb(80,100,220”; or as rgb plus alpha (opacity) such as “rgba(74,144,226,0.60)”.

display1.overlayFootprints(catalogSubset, color='rgba(74,144,226,0.50)',
                           highlightColor='yellow', selectColor='orange',
                           style='outline', layerString='detection footprints ',
                           titleString='catalog footprints ')

The layerString and titleString are concatenated with the frame, to make the footprint drawing layer name and the table title, respectively. If multiple footprint layers are desired, be sure to use different values of layerString.