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
Actions
VOTable object
Metadata tree
VOTable Parser
Display
VOTable document (SIA, IDHA, etc…)
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