CRDS uses command line tools or calibration software to identify and automatically download required reference files.
Working with CRDS references typically involves one or more of the following:
The current preferred approach is to install CRDS as part of Astroconda.
Onsite use generally requires no CRDS setup for JWST and uses shared CRDS files located under /grp/crds/cache.
# Typical onsite users and developers need no configuration for JWST.
For personal or offsite use, configuration requires defining:
setenv CRDS_PATH $HOME/crds_cache setenv CRDS_SERVER_URL https://jwst-crds.stsci.edu
export CRDS_PATH="$HOME/crds_cache" export CRDS_SERVER_URL="https://jwst-crds.stsci.edu"
This defines where personal copies of CRDS files are stored and which CRDS server is used.
Non-standard onsite configurations (TEST, I&T, DEV) require similar setup and designation of the appropriate server and cache area.
For JWST best references are assigned and/or downloaded transparently when calibration software is run.
Performing JWST Calibrations describes running JWST calibrations more generally, including implicitly CRDS.
Once initialized, CRDS can operate from cache when not connected to the Internet. In this disconnected mode CRDS runs normally but can only assign the best reference files known to the local cache.
CRDS creates and maintains your CRDS cache. Direct edits to files in the cache should be avoided.
Recalibrating to utilize new references should not require redownloading your datasets or previously cached reference files.