6.5 Transfer to CADC and CDS
6.5.1 Data products at CADC
The data products that are archived and distributed by CADC are all MD5 checksummed by terapix prior to
delivery to cadc. The MD5-checksum is calculated again immediately before and after the transfer, and the
checksum values are all preserved in the cadc archive. terapix verified the integrity of the whole T0007 release
by comparing the terapix and cadc checksum values. The checksums can be downloaded by the CFHTLS users
so any user can verify that the images are not corrupted after the transfer from cadc to his own
disk.
Note that prior to transfer all data are now compressed using gzip. There is no longer RICE compressed data in
the T0007 archived because all weight-map and stack images are not 16-bit Integer FITS files. CFHTLS users
also expressed a preference for gzipped data.
6.5.2 Data products at CDS
The Centre de Donnees astronomiques de Strasbourg (CDS) (?) provides several products derived from the
CFHTLS T0007 surveys:
- The catalog of observations: two tables (II/317/cfhtls_w, II/317/cfhtls_d), for Wide and Deep
surveys respectively (fields W1-W4: 35,651,677 sources; fields D1-D4: 2,293,851 sources). This
catalog is available via the VizieR catalog service (?) for any Web users and for Virtual-observatory
compatible tools such as Aladin (?) or Topcat (?). This catalog has been also integrated in the CDS
cross-match service (?) allowing it to be easily correlated with any other catalogue at the CDS;
- 10 multi-resolution all-sky previews (one preview per ugriz) band and one per survey (Wide, Deep)
and two coloured multi-resolution all-sky previews (based on ugi bands). Each preview allows one
to zoom and pan into the four fields of the CFHTLS (W1-W4 for the Wide survey, and D1-D4 for
the Deep survey) combined as a unique global sky (see Figure 51). These multi-resolution all-sky
previews can be visualised by Aladin or other compatible tools. These all-sky previews has been
generated from 9 recursive HEALPix sky tessellations from 52 to 0.2′′pixel angular resolution
(HEALPix Norder 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 found in the original image overlap regions. Pixels from 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) and in FITS encoded tiles
(true pixel values) (?).
These products are available through the following links :
Figure 51: | Upper panel: CFHTLS all-sky previews available via Aladin server. Lower Panel: From the
whole sky view to M101: an example of CFHTLS Wide u-band multi-resolution all-sky preview. |
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