Space-Time Coordinate Metadata RFC

This document will act as RFC centre for the Space-Time Metadata V1.21 Proposed Recommendation.

In order to add a comment to the document, please edit this page and add your comment to the list below in the format used for the example (include your WikiName so authors can contact you for further information). When the author(s) of the document have considered the comment, they will provide a response after the comment.

Discussion about any of the comments or responses should be conducted on the data model mailing list, dm@ivoa.net.

Comments

• The following comments affecting the document came from the VOEvent workshop (ArnoldRots - 16 May 2005):
  • Can Name in Coordinate be made optional?
  • What Frames should really be required in AstroCoordSystem?
  • Can the duplication of TimeScale in AstroCoordSystem and AstronTime be avoided?
  • XInclude examples in Appendix C?

• The following comments affecting the STC-X (schema) implementation came from the VOEvent workshop (ArnoldRots - 16 May 2005):
  • Can Observatory and Observation Locations be uncoupled?
  • Can multiple Observations and multiple coordinates be accommodated in ObsDataLocation?
  • Can AstroCoordArea be made optional in ObservationLocation?
  • Can there be an simpler description for error circles in the case of 2-D spatial coordinate systems?

I'm concerned about the amount of "implementation" that has been done to date. Could we have a definitive statement of what is serving as our 2 implementations?

I don't think having some example XML instance documents is sufficient for serving as an "implementation". We need actual software that actually does something with it. Use of STC in SkyNode does qualify; however, I think it is fair to say that this is only partial use. Something like the footprint service would perhaps provide more coverage of the schema. A stylesheet that converts STC into an astronomer-friendly description of a coordinate system, region, etc. would also be useful. It's not until a developer (because users are going to look at this stuff) actually sits down with STC and tries to use it will we understand if the schema does the job.

-- RayPlante - 16 May 2005

Responses

• The four requests from VOEvent affecting the document are reasonable and I will amend the document accordingly. The corresponding modifications to the schema implementation are minor and do not affect the validity of existing documents. ArnoldRots - 16 May 2005
  Specifically:
  • CoordName in Section 4.3.1 will be made optional.
  • SpectralFrame will be dropped from the list of required frames for AstroCoordSystem in Section 4.5.
  • TimeScale will be made optional in AstronTime in Section 4.6.1.1, though it will be stressed that it should only be omitted if that element is associated with and AstroCoordSystem.
  • I will suggest a standard naming of XInclude files and the IDs they contain, to reflect their contents and provide examples for ICRS-TT-TOPO and FK5-UTC-TOPO as representing commonly used cases.

• As to the four comments from VOEvent on the schema implementation: the last two are minor and will be implemented, while the first two need additional study; none of them affect the PR or existing documents based on the schemata. ArnoldRots - 16 May 2005

• A few typos were pointed out and a suggestion for improvement (use of different units) was made for the example in Appendix B.4: The coord_system_id should be "ICRS-TT-TOPO", the wavelength units might be changed to "nm", the Start and Stop Times need to be corrected, and the pixel number upper limits need to be corrected. These changes will be made. ArnoldRots - 16 May 2005

• A query from the Catalog group made me realize that 3-D spherical coordinates need to be extended to allow "deg deg Mpc" as units in Section 4.5.2.2; this will be accommodated. ArnoldRots - 16 May 2005