A.4.5.9 XYCorr Form

The XYCorr () form plots an error ellipse (or rectangle or other similar figure) defined by errors in the X and Y directions, and a correlation between the two errors.

The supplied correlation is a dimensionless value in the range -1..+1 and is equal to the covariance divided by the product of the X and Y errors. The covariance matrix is thus:

   [  xerr*xerr         xerr*yerr*xycorr  ]
   [  xerr*yerr*xycorr  yerr*yerr         ]

This plot type is suitable for use with the <x>_error and <x>_<y>_corr columns in the Gaia source catalogue.

Example XYCorr plot

XYCorr form configuration panel

The configuration options are:

Shading Mode

See Appendix A.4.6.

X/Y Error

The error along the horizontal and vertical directions, as column names or expressions.

XY Correlation

Correlation beteween the errors in the horizontal and vertical directions. This is a dimensionless quantity in the range -1..+1, and is equivalent to the covariance divided by the product of the X and Y error values themselves. It corresponds to the x_y_corr values supplied in the Gaia source catalogue.

Ellipse

Ellipse graphical representation, selected from a range of options (includes also rectangles, crosses etc).

Thickness

Controls the line thickness used when drawing polygons. Zero, the default value, means a 1-pixel-wide line is used. Larger values make drawn lines thicker, but note changing this value will not affect all shapes, for instance filled polygons contain no line drawings.

Scale

Adjusts the size of variable-sized markers like vectors and ellipses. The default value is 1, smaller or larger values multiply the visible sizes accordingly.

Autoscale

Determines whether plotted ellipses are automatically scaled to have a sensible size. If true, then the sizes of all the ellipse markers are examined, and some dynamically calculated factor is applied to them all to make them a sensible size (by default, the largest ones will be a few tens of pixels). If false, the sizes will be the actual input values interpreted in data coordinates. If auto-scaling is on, then markers will keep approximately the same screen size during zoom operations; if it's off, they will keep the same size in data coordinates.