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#### 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).

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
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