The SkyDensity form ()
plots a density map on the sky using a HEALPix grid
with a configurable resolution.
You can optionally use a weighting for the data values to accumulate
within each HEALPix tile,
and you can configure how the weighted values are combined to
generate the eventual pixel values (and hence colours).
HEALPix
is a tiling scheme for the sky which uses square-ish pixels
of equal area to cover the celestial sphere.
The shading is done using the shared colour map. This colour map is used by all currently visible SkyDensity, Grid, Aux and Weighted layers. When at least one such layer is being plotted, the Aux Axis control is visible in the control panel, which allows you to configure the colour map, range, ramp display etc.
Example SkyDensity plot
SkyDensity form configuration panel
The configuration options are:
For density-like values
(count-per-unit
, sum-per-unit
)
the scaling is additionally influenced by the
Per Unit option.
The following options (some are more useful than others) are currently available:
sum
:
the sum of all the combined values per binsum-per-unit
:
the sum of all the combined values per unit of bin sizecount
:
the number of non-blank values per bin (weight is ignored)count-per-unit
:
the number of non-blank values per unit of bin size
(weight is ignored)mean
:
the mean of the combined valuesmedian
:
the median of the combined values (may be slow)min
: the minimum of all the combined valuesmax
: the maximum of all the combined valuesstdev
:
the sample standard deviation of the combined valueshit
:
1 if any values present, NaN otherwise (weight is ignored)count-per-unit
or sum-per-unit
).
If the Combination mode is calculating values per unit area,
this configures the area scale in question.
For non-density-like combination modes
(e.g. sum
or mean
)
it has no effect.
The available options are:
steradian
: steradiandegree2
: square degreearcmin2
: square arcminutearcsec2
: square arcsecondmas2
: square milliarcsecuas2
: square microarcsecThe Report panel provides information calculated by the plot: