A VO experience:Lessons learnt from accessing

SIA compliant image servers with the AVO prototype

F.Bonnarel on behalf of M.Allen, T.Boch, M.Dolensky, D.Durand, P.Fernique, M.Louys, A.Micol, A.Richards, A.Schaaff, N.Walton

A VO experience

Image access for the AVO scientific demo:

– Use ALADIN as the core display system for the AVO prototype.

– Two types of image access:• Using the CDS image server (e.g. GOODS data

provided by ESO, STScI)• Other external image servers (e.g. CHANDRA)

– Visualize the field of views.– Image cut-out limits on previews.

A VO experience

• Accessing image data before SIA– Images qualifiers stored in the CDS image

server– Links to the images via URL stored in the

observation logs from VIZIER– Links to other servers using miscellaneous

methods (SKYVIEW, DSS servers, SuperCosmos). GLU descriptions. Availability problem.

A VO experience

• Accessing image data with SIA - the availability issue.

– Common request syntax– Using “standard” metadata

• To describe images of all the compliant servers• To formulate queries using the metadata

– Using “standard” access layer. Agreement on the required and optional metadata fields

– Allow distributed image access (no need to store everything at one place)

A VO experience

• Problems found with present SIA compliant servers:

• Wrong URLs• Wrong UCDs (VOX:Image_AccessReference)• Required fields missing (Image_Title,

Image_Scale, Image_Naxis)• Useful optional fields missing (BandPass_ID,

WCS)• SIA 1.1 will provide data collection field• Other SIA 1.0 limitations discussed during the

interoperability meeting

A VO experience

Writing a SIA interface: the AVO prototype example.

– Need for a VOTable parser: (SAVOT) ---> a VOTable object in memory

– Need for a visual structure manipulation: the metadata tree

– The TreeBuilder provides flexible organisation of VOTable fields and resources in the metadata tree.

– In addition to metadata display, the interface can use the metadata to draw observation centres, FOV, etc..

A VO experience

Accessing image data: metadata factorization issue.– Parallel development of the IDHA VOTable and SIA for

the purposes of the AVO scientific demonstration.

– main difference with SIA is that factorization of the metadata is possible in IDHA

– main part of the AVO prototype chain from the VOTable document to the metadata tree is the same for both SIA and IDHA VOTables

– Other kinds of VOTable descriptions of the metadata could be integrated in the same way (e.g future versions of SIA)

How is it working?

TreeBuilder

VOTable Parser

Metadata tree

VOTable document (SIA, IDHA, etc…)

VOTable object

Actions

Display

A VO experience

• Image data accessible from the AVO prototype:– SIA servers at NOAO, Skyview, CADC,

NCSA, Skyview, IPAC, XMM-Newton, SDSS, CDS, NAOJ, etc...

– IDHA servers at CDS, and HST facilities– IDHA local document accessing image data at

Jodrell Bank – Local SIA VOTABLES document could also

be read

A VO experience

• Some Key Words:– The ALADIN Java interface– AVO prototype– VOtable1.0– Metadata tree – SIA 1.0 VOtables– IDHA VOtables– IDHA model