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Check Flags

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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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