Build on existing coadds?

Support
#1

Dear all,

Is there a way to add extra exposures to an existing set of coadds? For example, generating a set of coadds from exposures from night 1 then adding to these with exposures from night 2 (3, 4, etc.) without having to re-warp etc. the exposures from night 1? In this example, the exposures from night 2 would either increase the depth of the coadds (if they were co-spatial) or extend the area covered by the coadds (if they were not co-spatial).

Sorry if we’re missing something obvious here, but we’ve poked around through the stack and available documentation and the only thing we’ve found that may help is addExposure in lsst.coadd.utils.coadd. However, this doesn’t seem to be called by any of the pipe_tasks or pipe_drivers.

Thanks,

James

#2

There is no easy way to do this; the low-level code could do it, but you’d need to write some new high-level code to put it all together, and the safe-clipping algorithm for removing junk may not work.

If you’re concerned about computation time, it’s worth pointing out that the actually coaddition process is quite fast compared to warping the images (the makeCoaddTempExp.py stage). So if you just run that on the additional images and re-run all of coaddition, you’ll still spend most of your time on the makeCoaddTempExp.py step anyway.

#3

Thanks for the quick reply. It’s useful to know that this isn’t implemented in the stack and so it’s not simply that we aren’t aware of the correct procedure to use.

My concern is, indeed, computation time, so I really welcome your suggestion of just warping the new images and re-running all the coaddition.

Thanks!