For the RSP image metadata services, based on the IVOA ObsCore model (initially ObsTAP and later also SIAv2) we have adopted the "CADC model" where the access_url  in the ObsCore data model is a link, not directly to the image, but to a DataLink "links service" which provides access to the image and (extensibly, over time) to a variety of related information.

IVOA Documentation:

  • ObsCore v1.1: abstract, PDF
    • Definition of access_format  when using a links service for access_url: end of section 4.7
  • DataLink v1.0: abstract, HTML

Most immediately we need to decide on what the URL TO  the links service will be, for each image, e.g., something of the form:

... and on what the links service itself will return as a URL, which must be directly usable via GET, for the underlying image file itself.

Update from  meeting:

  • The links service will live at https://data.lsst.cloud/api/datalink/links .
  • The ID parameter's value will have the format butler://dp02/{uuid} , where uuid  is the standard Gen3 Butler UUID string.
  • Escaping for the ID parameter's value will be a matter for SQuaRE to work out.  It's possible only the ":" will need to be escaped.
  • Tim Jenness , what if we need/want to use this, beyond DP0.2, for a Butler repo that doesn't have a "short name" yet?
  • The "links service" itself will be responsible for creating a Butler based on the "dp02" part of the string, then using that Butler to translate the UUID into a Google Cloud S3 URI for the underlying file artifact, and then finally for obtaining a signed URL for that artifact that is usable externally for a limited time.
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