7.2.1 Data integration
Author(s): Alex Hutton and Enrique Utrilla
As described in previous sections, the data received from Gaia follows a chain of processes focused in different aspects. Typically each of these specialised processes uses only the part of the data available for each source that is relevant for it, discarding the rest. In other cases, output is generated only for a subset of the sources. For this reason the output of different processes has to be combined with the original data as part of the cyclic processing to generate a complete record with all the information available for each source.
From the point of view of astrometry, the core of this integration process is the combination of the data from IDU, which provides the cross-match of individual observations into sources, and AGIS, that generates an astrometric solution for the sources, as well as data from the initial catalogue.
In particular, for Gaia EDR3 the astrometry datasets to be integrated are the following:
The complete, unfiltered list of sources obtained in cycle 2, from which the Gaia DR2 catalogue was extracted. This includes data integrated from the AGIS, IDU and the initial IGSL catalogue in cycles 1 and 2.
The lists of new, updated and removed sources as a result of the processing in IDU of the cycle 3 data (IDU-03 - see Section 3.4.13). This process can result in the merging of two previously separate sources, or the split of the observations previously assigned to a single source into two or more, or the deletion of a source based on previous spurious observations.
The astrometry produced by AGIS for these cycle 3 sources (AGIS-03).
Additionally in Gaia EDR3, the detailed photometry produced by the photometric data processing are merged into the source records.
This integration process is carried out by a dedicated software called the MDB Integrator.