Planck 857 GHz Survey: I

In order to visualize the polarization information, it is highly recommended that the data be resampled with the "Clip (intensive)" sampler and the result smoothed. That sampler will average all the data points within a given output pixel rather than the more common nearest neighbor. It will do this averaging before computing either PI or PA to reduce the effects of the noise.

This sampler is set as the default for this survey. If the output pixel resolution is not significantly larger than the resolution, a smoothing of the output pixels will also be necessary. <p> Note also that Q and U are defined relative to a given co-ordinate system, in this case Galactic, and following the CMB convention (not the IAU); see lambda.gsfc.nasa.gov/product/about/pol_convention.cfm. This means that they will appear to vary rapidly near the pole of that coordinate system.

The PI and PA will be computed correctly for any position on the sky. <p> The original data are stored in HEALPix pixels. SkyView treats HEALPix as a standard projection but assumes that the HEALPix data is in a projection plane with a rotation of -45 degrees. The rotation transforms the HEALPix pixels from diamonds to squares so that the boundaries of the pixels are treated properly.

The special HealPixImage class is used so that SkyView can use the HEALPix FITS files directly. The HealPixImage simulates a rectangular image but translates the pixels from that image to the nested HEALPix structure that is used by the HEALPix data. Users of the SkyView Jar will be able to access this survey through the web but performance may be poor since the FITS files are 150 to 600 MB in size and must be completely read in.

SkyView will not automatically cache these files on the user machine as is done for non-HEALPix surveys. </p> Data from the frequencies of 100 GHz or higher are stored in a HEALPix file with a resolution of approximately 1.7' while lower frequencies are stored with half that resolution, approximately 3.4'. Provenance: Data split using skyview.survey.HealPixSplitter from the PR3 distriuted by the Planck Science team.. This is a service of NASA HEASARC.