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How do I...
Find out if SDSS's imaging data for an object are reliable?
The SDSS does automatic processing to determine the reliability of the imaging data
for each of the 14 million objects that it has seen. The reliability information is
stored in flags data in the PhotoObj
table in the database. Understanding the flags is extremely important for doing science,
so that you can understand what data are reliable.
By using several flags together, you can search for only objects that have clean photometry.
Skip to clean photometry search guide
Flags are yes/no parameters. If a certain flag (such as Saturated) is present for an object,
the object has that characteristic (i.e. its image is saturated). To save space in the database, the
flags are stored as zeros (absent) or ones (present). Each object has a long bitwise number
associated with it, where each set of digits corresponds to one flag. The database includes
functions that translate back and forth between the binary numbers and the flag names.
You can view flag names directly with the
Explore tool (link opens in new window), but to work with flags in search results, you will
need to know how to use the translate functions.
Next: Check what flags are present for a single object
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