The PS1 object identifiers (
objID in the database tables) are computed from the object positions. We do not recommend trying to extract the positions directly from the
objID because subsequent calibrations have significantly improved the positional accuracy of the RA and Dec columns. However, the
objID is the primary key in most PS1 tables, and it is useful to know how the
objID is related to position. Partitioning the table by
objID approximately divides the table into declination strips.
How the object identifier is computed from RA and Dec
objID index is derived from right ascension and declination. While it is possible to calculate the RA and Dec from the
objID, it is not recommended to do this, because the
objID is based on the astrometric solutions from individual exposures and stacks as they are ingested during an early phase of the PS1 data processing. Consequently the positions derived from the
objID have not been calibrated against 2MASS or Gaia. It is recommended to use
decMean from ObjectThin. Included below is the C code for the translation between R.A. and Dec., for users interested in the relationship.
The figure below (adapted from a similar figure from Heather Flewelling) shows an example of computing the
objID from specific RA and Dec values.