Apzip · Working & Fast

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

The APZIP procedure uses a three-step custom algorithm to achieve an average compression factor of approximately . : Compressed files generated by APZIP are saved with the

: The resulting multi-extension FITS files are compressed using the FPACK utility and the lossless Rice compression algorithm . 3. Usage and Accessibility APZIP was created to speed up data transfer

: Detector reads are converted into difference images (the first read plus difference images) to reduce dynamic range. : Compressed files generated by APZIP are saved with the

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

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

: The corresponding program APUNZIP.PRO is used to restore the raw data cubes for reduction.