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We now go to greater lengths to check that the information in the file is consistent with the LSST standard, warning the user – and in some cases refusing to proceed – if it does not.
(DM-2599)
Improved support for non-standard FITS headers
The LSST stack is now capable of loading FITS files which contain non-standard headers of the form PVi_nn (i=1..x, nn=5..16), as written by SCAMP, and EQUINOX headers with a "J" prefix, as written by SkyMapper.
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See the description of the multi-band coadd processing work performed in S15 for details. In short, four new command-line Tasks have been added for consistent multi-band coadd processing:
DetectCoaddSourcesTask
- Detect Detect sources (generate Footprints for parent sources) and model background for a single band.
MergeDetectionsTask
- Merge Merge Footprints and Peaks from all detection images into a single, consistent set of Footprints and Peaks.
MeasureMergedCoaddSourcesTask
- Deblend Deblend and measure on per-band coadds, starting from consistent Footprints and Peaks for parent objects.
MergeMeasurementsTask
- Combine Combine separate measurements from different bands into a catalog suitable for driving forced photometry. Essentially, it must have a centroid, shape, and CModel fit for all objects, even for objects that were not detected on the canonical band. Will assume that all input catalogs already have consistent object lists.
(DM-1945, DM-3139)
Enable use of deblended HeavyFootprints in coadd forced photometry
Given the new multi-band processing for coadds (above), we now have a reference catalog that is consistent across all bands. This catalog allows the use of the source's HeavyFootprints to replace neighbors with noise in forced photometry, thus providing deblended forced photometry and consistent deblending across all bands. This provides much better colors for blended objects as well as measurements for drop-out objects that do not get detected in the canonical band. This functionality has been enabled for forced coadd photometry.
See the description of the multi-band coadd processing work performed in S15 for further motivation of this change.
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Large Footprints may be skipped on initial processing
For practical processing purposes (specifically total processing time and memory limits due to current hardware limitations), we have the option to skip over objects with large Footprints during large-scale processing, with the intention to return to these objects to "reprocess" them using different hardware in future. The ability to properly record which objects have been skipped and require further processing has been implemented along with optimizations with optimizations to the deblender configuration for the maximum number of Peaks per Footprint, and the size and area of Footprints.
(DM-2914)
Command line tasks for measurement transformation
The measurement transformation framework provides a generic mechanism for transforming the outputs of measurement plugins in raw units, such as pixel positions or flux, to calibrated, physical units, such as celestial coordinates or magnitudes. Appropriate transformations are defined on a per-measurement-plugin basis, and may make use of the calibration information and WCS stored with the data.
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A number of minor changes and documentation improvements were made to the CoaddBase, AssembleCoadd, CoaddInputRecorder and MakeCoaddTempExp tasks. These brought the structure of the code better into line with the state-of-the-art development on Hyper Suprime Cam.
(DM-2980)
Properly handle masking NaN or saturated values in overscans
Resolved an issue where, in certain circumstances, flags in the mask plane for saturated and nan values in overscans were being improperly propagated to all amplifiers in an image. These flags are now applied to the amplifier where the bad values are seen.
(DM-2923)
Deblender optimization
Several performance optimizations to the (C++) algorithms used in the deblender have been implemented, in particular those which identify objects with significant amounts of their flux attributed to edge pixels. In addition, memory memory usage was reduced by removing unused mask planes left over from debugging, not storing masks for deblending templates, and by clipping template images when their associated Footprints are clipped.
(DM-2914)