Virtual Observatory: the CFHTLS at CDS
The Centre de Données astronomiques de Strasbourg (CDS) [1] provides several products derived from the final CFHTLS release (T0007):
  • The catalog of observations in VizieR: two tables (II/317/cfhtls_w, II/317/cfhtls_d), respectively the Wide survey (fields W1--W4: 35,651,677 sources) and the Deep survey (fields D1--D4: 2,293,851 sources). This catalog is available via the well known VizieR catalog service [2] for any Web users and for "VO compatible tools" such as Aladin [3] or TOPcat [4]. This catalog has been also integrated in the CDS cross-match service [5] allowing one to easily correlate data with any other catalog distributed by the CDS.

  • Ten multi-resolution all-sky previews in Aladin (one preview per band u*, g', r', i', z') and per survey (Wide, Deep) and 2 colored multi-resolution all-sky previews (based on u*+g'+r' bands). Each preview enables one to zoom and pan into the individual CFHTLS fields (W1-W4 for the Wide survey, and D1-D4 for the Deep survey) combined within a unique global sky (see illustration below). These multi-resolution all-sky previews can be visualized by Aladin [3] or other compatible tools. These all-sky previews have been generated through 9 recursive HEALPix sky tessellations from 52 to 0.2 arcsec pixel angular resolution (HEALPix N-order 3 to 11) using a bilinear resampling from the original images to the deeper HEALPix grid (Norder 11). A weighted average based on the distance to the border has been applied on the pixels localized in the original image overlapping regions. A pixel from a HEALPix order N is the average value of the 4 corresponding HEALPix pixels of the order N+1. The all-sky previews are delivered in JPEG encoded tiles (8 bits pixel values - compressed) as well as in FITS encoded tiles (true pixel values) [6].

  • [1] Genova F., Egret D. et al., Astron. Astrophys., Suppl. Ser., 143, 1-7, 2000
    "The CDS information hub. On-line services and links at the Centre de Donnees astronomiques de Strasbourg"
  • [2] Ochsenbein F. et al., Astron. Astrophys., Suppl. Ser., 143, 23-32, 2000
    "The VizieR database of astronomical catalogues."
  • [3] Bonnarel F., Fernique P. et al., Astron. Astrophys., Suppl. Ser., 143, 33-40, 2000
    "The ALADIN interactive sky atlas. A reference tool for identification of astronomical sources"
  • [4] Taylor M.B., Vol. 347. Astronomical Society of the Pacific, 2005., p.29
    "TOPCAT& STIL: Starlink Table/VOTable Processing Software"
  • [5] Pineau F.-X.; Boch T. et al., Vol. 442. Astronomical Society of the Pacific, 2011., p.85
    "Efficient and Scalable Cross-Matching of (Very) Large Catalogs"
  • [6] Fernique P., Oberto A. et al., Vol. 434. Astronomical Society of the Pacific, 2010., p.163
    "Another Way to Explore the Sky: HEALPix Usage in Aladin Full Sky Mode"

CFHTLS all-sky previews available via the Aladin server form. Credit: CDS

From the whole sky view to Messier 101 details
in the CFHTLS Wide u* multi-resolution all-sky preview (WIDE-U). Credit: CDS