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In the next major release of the LSST stack, the system for measuring the properties of sources will be replaced by a new one, housed mostly in the new meas_base package. In addition to providing new Task classes and a new plugin interface for measurement algorithms, this overhaul also includes changes to the schemas of the catalogs produced by the measurement framework. The new framework will not be entirely complete as of the next release, but it will have sufficient functionality to replace the old framework as the default. The old system will remain available via config on the S14 final release, but will be removed entirely before the W15 release.
New Tasks
The main entry point for the new measurement framework is the new SingleFrameMeasurementTask class (in meas_base), which is intended as an almost drop-in replacement for the current SourceMeasurementTask (in meas_algorithms). It's not drop-in replacement, because it has different plugins, a slightly different slot system, and an entirely different output schema - so we will use it everywhere SourceMeasurementTask was used before, but many other additional configuration settings need to be modified when retargeting the measurement task to keep it all working. We've provided configuration files to make that easy, as described in the next section.
SingleFrameMeasurementTask combines the work previously done by two classes, the old SourceMeasurementTask and the C++ MeasureSources class. It initializes the plugins (which determines the schema) in its constructor, then invokes the plugins on each source in the image, replacing neighbors with noise as it does so (this is delegated to the NoiseReplacer class, which replaces the ReplaceWithNoiseTask subtask). Unlike SourceMeasurementTask, SingleFrameMeasurementTask does not do forced photometry (see below). Sources are also processed in a slightly different order (see Simultaneous Multi-Object Measurement).