Best way to warp a PSF to match a warped image?

[charlotteaward (Charlotte Ward)]

Hello!

I’ve created warped cutouts following the examples in tutorial-notebooks/DP0.2/13a_Image_Cutout_SciDemo.ipynb at main · lsst/tutorial-notebooks · GitHub and would like to warp their corresponding PSFs so they match the new WCS. The warpExposure documentation recommends using WarpedPSF (Class WarpedPsf — LSST Science Pipelines) and I was wondering how to best obtain the inputs for this function. I currently obtain PSFs using, for example info_calexp = img.getInfo() psf_calexp = info_calexp.getPsf() and have the WCS of the warped images using img.getWcs() but am having trouble tracking down how to get the right input formats for WarpedPSF!

Many thanks!

[ameisner (Aaron Meisner)]

Hi @charlotteaward – thanks for your message. Another community member recently posted an example of using WarpedPsf :

Issues with Image Subtraction

Hi everyone, So I think I’ve figured it out. I wanted to share my solution in case anyone else wants to do this. The first step involves obtaining the sources in the visit image and making sure that the final SourceCatalog has the right columns. from lsst.meas.algorithms.detection import SourceDetectionTask from lsst.meas.deblender import SourceDeblendTask from lsst.meas.base import SingleFrameMeasurementTask import lsst.daf.base as dafBase calexp.mask.removeAndClearMaskPlane('DETECTED') sch…

Specifically the lines:

xyTransform = afwGeom.makeWcsPairTransform(template.wcs,calexp.wcs)
warpedPsf = measAlgorithms.WarpedPsf(template.psf, xyTransform)

Does that approach (passing an output from afwGeom.makeWcsPairTransform as an input to WarpedPsf) work for you? Thanks again.

[charlotteaward (Charlotte Ward)]

Yes!!! This worked!! Thank you very much