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SDSS ObjID Encoding

The bit encoding for the long (64-bit) IDs that are used as unique keys in the SDSS catalog tables is described here.


The encoding of the photometric object long ID (objID in the photo tables) is described in the table below. This scheme applies to the fieldID and objID (objid bits are 0 for fieldID).

Bits Length
(# of bits)
Mask Assignment Description
0 1 0x8000000000000000 empty unassigned
1-4 4 0x7800000000000000 skyVersion resolved sky version (0=TARGET, 1=BEST, 2-15=RUNS)
5-15 11 0x07FF000000000000 rerun number of pipeline rerun
16-31 16 0x0000FFFF00000000 run run number
32-34 3 0x00000000E0000000 camcol camera column (1-6)
35 1 0x0000000010000000 firstField is this the first field in segment?
36-47 12 0x000000000FFF0000 field field number within run
48-63 16 0x000000000000FFFF object object number within field


The encoding of the long ID for spectroscopic objects is described below. This applies to plateID, specObjID, specLineID, specLineIndexID, elRedshiftID and xcRedshiftID.

Bits Length
(# of bits)
Mask Assignment Description
0-15 16 0xFFFF000000000000 plate number of spectroscopic plate
16-31 16 0x0000FFFF00000000 MJD MJD (date) plate was observed
32-41 10 0x00000000FFC00000 fiberID number of spectroscopic fiber on plate (1-640)
42-47 6 0x00000000003F0000 type type of targeted object
48-63 16 0x000000000000FFFF line/redshift/index 0 for SpecObj, else number of spectroscopic line (SpecLine) or index (SpecLineIndex) or redshift (ELRedhsift or XCRedshift)