You can read parts of exposures with something like
exp = butler.get("calexp_sub", bbox=XXX, ...)
Is there a way to specify PARENT or LOCAL? I can’t find any documentation of what get supports – pointers welcome.
You can specify imageOrigin="PARENT" or imageOrigin="LOCAL". This is not documented, and in the current model there is no single good place to document this. (It’s a conspiracy between code in lsst.daf.butlerUtils.CameraMapper and lsst.afw.formatters.ExposureFormatter and a little bit of your obs package’s PAF file, none of which are directly visible to lsst.daf.persistence.Butler.get(), which is just a generic interface.)