Apzip

The theoretical maximum compression for APOGEE's noise levels and bit depth is approximately 2.6. In practice, APZIP’s compression of ~2.0 is considered as good as can be expected for the specific astrophysical data it handles.

: An average difference image is computed and subtracted from all difference images, resulting in "residual" images that are easier to compress.

: Detector reads are converted into difference images (the first read plus difference images) to reduce dynamic range. : Detector reads are converted into difference images

: The resulting multi-extension FITS files are compressed using the FPACK utility and the lossless Rice compression algorithm . 3. Usage and Accessibility

: The APZIP code is part of the apogeereduce software product. While primarily an internal tool for the Sloan Digital Sky Survey (SDSS) , versions of the pipeline are hosted in public repositories like the SDSS-III SVN repository. 4. Comparative Efficiency Usage and Accessibility : The APZIP code is

The APOGEE instrument produces roughly and up to 100 GB per night . APZIP was created to speed up data transfer from the Apache Point Observatory to the Science Archive Server (SAS) and to minimize overall disk usage. It compresses raw data cubes by taking advantage of the fact that successive reads of the detector arrays are highly similar. 2. Technical Compression Algorithm

The APZIP procedure uses a three-step custom algorithm to achieve an average compression factor of approximately . : Detector reads are converted into difference images

: Compressed files generated by APZIP are saved with the .apz extension.