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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 1pixelwide 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 variablesized 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 autoscaling 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.
Next Previous Up Contents
Next: SkyCorr Form
Up: Plot Forms
Previous: SkyEllipse Form
TOPCAT  Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page:
http://www.starlink.ac.uk/topcat/
Author email:
m.b.taylor@bristol.ac.uk
Mailing list:
topcatuser@jiscmail.ac.uk