The warping implementation (currently MakeCoaddTempExpTask) relies on a SelectImagesTask to sort out the inputs. Unfortunately, this selection is performed inside the MakeCoaddTempExp.run method, which means MakeCoaddTempExpTask gets parallelised over patches rather than over individual warps (unless the user has some additional mechanics for setting the command-lines, essentially doing the selection themselves), which is inefficient. The SelectImagesTask hierarchy grew up as a MySQL database query before other things got tacked on to support butler-based selection, and could use simplification.

I propose to move the selection of images into the TaskRunner.getTargetList method, which will allow for parallelisation over individual warps. I will also refactor the SelectImagesTask hierarchy and add a sub-class to perform selection of images using the spatial database introduced in DM-3472.

There is a SelectSdssImagesTask in obs_sdss that I propose to drop because it relies on a particular database that I don't have access to and cannot recreate, and that code probably hasn't been used in a while. If someone objects to dropping it, I will attempt to modify it to conform with the SelectImagesTask changes, but testing and fixing it will have to be the responsibility of whoever wants to keep it.

While I'm modifying the warping front-end, I also propose to move the config parameters that are operational in nature (e.g., doWrite, doOverwrite) out of the Config. Their presence in the Config causes trouble because there are legitimate reasons for changing their values between command-line incantations, but doing so requires adding --clobber-config which should only be required for changes of an algorithmic nature.