VObs.it Osservatorio Virtuale Italiano

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VObs.it Osservatorio Virtuale Italiano

• Simple Cone Search (SCS)
• Simple Image Access (SIA)
• C.A. Volpicelli

INAF - Monte Porzio Catone ,23-24 novembre 2006
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Simple Cone Search

• Summary
• Simplest possible access to astronomical catalogs
• By far the most widely implemented VO data
  service
• Query Parameters
• RA, DEC Position on the sky (J2000,
  DDEG)
• SR Search radius (DDEG)
• VERB Verbosity (levels 1-3, optional)
• There may be other parameters

INAF - Monte Porzio Catone ,23-24 novembre 2006
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Simple Cone Search

• Query Response
• VOTable v1.0 UCDs describe columns
• VOTable MUST comply with these conditions
• Single RESOURCE with single TABLE
• TABLE must have FIELDs where the following UCD
  have been set
• Exactly one FIELD must have ucdID_MAIN
  (string) pepresenting an ID string for that
  record of the table
• Exactly one FIELD must have ucdPOS_EQ_RA_MAIN
• Exactly one FIELD must have ucdPOS_EQ_DEC_MAIN
• In case of error, the service MUST respond with a
  VOTable that contains a single parameter called
  ERROR.
• In case of empty return from the query it should
  return a VOTable with metadata without data
  records.

IVOA Working Draft Simple Cone Search V. 1.0
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Esempio
INAF - Monte Porzio Catone ,23-24 novembre 2006
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SIA Protocol

• SIA is designed primarily an an image on
  demande service, with images created on-the-fly
  by the service given the position and size of the
  desired output image
• Represents a negotiation between the client and
  the image service.The client describes the ideal
  image- what it would like to get back from the
  image service- and the image service return a
  list, encoded as a VOTable, of the (often
  virtual) images it can actually return.

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Simple Image Access (SIA V1.0)

• Summary
• Uniform access to 2 dimensional images
• Basically 2-D, but data model and interface are
  more general
• Same service profile as Cone, but adds getData
• The query is now used for data discovery instead
  of data access as for Cone data access is a
  separate operation
• Prototype for 2nd generation DAL interfaces
• multiple output formats, virtual data generation,
  etc.

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SIA ConceptsService Type

• These categories are use primarily to
  charaterize the service as part of Service
  Registration, to aid the clients in discovering
  the services best suited to their needs.
• Atlas Pre-computed survey image (entire image)
• Pointed Image from pointed observation (entire
  image), instrumental archives ( HST, GALEX, .)
• Cutout Cutout existing image (pixels unchanged) ,
  returning an image of the requested size to the
  client
• Mosaic Reprojected image (pixels re-sampled),
  similar to the cutout but add the capability to
  compute an image of the size, scale, and
  projection specified by the client
• SIA data model is the familiar "astronomical
  image"
• Generally this means a 2D sky projection, but
  cubes too
• Data array is logically a regular grid of pixels
• Encoded as a FITS image, GIF/JPEG, etc.

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SIA Input Parameters

• Required parameters
• POS center of ROI (ra, dec decimal degrees ICRS)
• SIZE the angular size of the region in decimal
  degrees width or width, height
• SIZE0 For atlas or pointed image archive this
  tests whether the given point is in any image.
  For cutout or mosaic service a default sized
  image is returned
• FORMAT ALL, GRAPHIC, image/fits, image/jpeg,
  text/html, FORMATmetadata returns service
  metadata
• Optional parameters
• INTERSECT values covers, enclosed, center,
  overlaps
• VERB Table verbosity , integer value ( 0 - 3)
  .Indicates the desired level of information to
  be returned in the output table
• Service-defined parameters
• used to further refine queries, but not yet
  standardized
• e.g., BAND, SURVEY, etc.
• Image generation parameters
• NAXIS, CFRAME, EQUINOX, CRPIX, CRVAL, CDELT,
  ROTANG, PROJ
• used for cutout/mosaic services to specify image
  to be generated

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SIA Input Parameters

• Image Generation Parameters
• The service MAY support the following image
  generation parameters (IGP) which are used to
  specify the desired size, scale, and orientation
  of the output image.
• These parameters are provided for the cutout and
  mosaicing services which generate images upon
  demand. Services which do not support these
  parameters may ignore them, but MUST allow them
  to be present without error.
• NAXIS,CFRAME,EQUINOX,CRPIX,CRVAL,
• CDELT,ROTANG,PROJ

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SIA Query Response

• Output is a VOTable
• Must contain a RESOURCE element with
  tag"results", containing the results of the
  query.
• The results resource contains a single table
• Each row of the table describes a single data
  object which can be retrieved.
• The FIELDs of the table describe the attributes
  of the dataset
• In SIA 1.0, the UCD is used to identify the data
  model attribute
• e.g., POS_EQ_RA_MAIN, VOXImage_Scale, etc.

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SIA Image Metadata (UCDs)

• VOXImage_Title Brief description of image
• POS_EQ_RA_MAIN Ra (ICRS)
• POS_EQ_DEC_MAIN Dec (ICRS)
• INST_ID Instrument name
• VOXImage_MJDateObs MJD of observation
• VOXImage_Naxes Number of image axes
• VOXImage_Naxis Length of each axis
• VOXImage_Scale Image scale, deg/pix
• VOXImage_Format Image file format
• VOX defines a temporary namespace for UCD-like
  terms defining experimental concepts used in VO
  prototypes.

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SIA Access Metadata

• VOXImage_AccessReference (required)
• specifying the URL to be used to access or
  retrieve the image
• Not point to an actual existing online image,
  could point to a virtual image, which will be
  generate on-the-fly.
• VOXImage_AccessRefTTL
• Specifying the minimum time to live in seconds of
  the access reference
• VOXImage_FileSize
• Representing the actual or estimated size of the
  encoded image in bytes ( not pixel)

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SIA Query Response

• Image metadata
• Describes the image object (required)
• Coordinate system metadata
• Image WCS
• Spectral bandpass metadata
• Prototype data model describing spectral bandpass
  of image
• Processing metadata
• Tells whether the service modified the image
  data
• Access metadata
• Tells client how to access the dataset
  (required)
• Resource-specific metadata
• Additional optional service-defined metadata
  describing image

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Image Retrieval

• Retrieval is optional
• Typically only a fraction of the available images
  are retrievedBased on query response
• If an access reference is provided, the data can
  be retrieved
• SIAP can also be used to describe data which is
  not online
• The same data may be available in multiple
  formatsImage retrieval
• Very simple access reference is a URL
• Standard tools can be used to fetch the data
• (browser, wget, curl, i/o library, etc.)
• Data is often computed on-the-fly
• All retrieval is synchronous (currently)
• No provision for restricting access (currently)