ELLIPSES

Draw error ellipses

Description:

Draw error ellipses at each of the data points using values in the EXCOL and EYCOL error data areas, and the ZCOL data values as the normalised covariance. Depending upon the value of the AXES parameter, the major and minor axes of the ellipses will also be drawn.

The size of the ellipses depends upon the parameter ERSCALE which should be set before the data are read in so that the WORLD application can calculate the viewing area properly. This allows the ellipse size to be varied so that it can be drawn for different confidence levels.

ERSCALE Confidence
level
1.00 46%
2.30 68.3%
4.61 90%
9.21 99%

Usage:

ellipses [axes] [erscale]

Parameters:

AXES = _LOGICAL (Read and Write)
If TRUE, the axes of the ellipses will be drawn.

If the value is not specified on the command line, the current value is used. The current value is initially set to FALSE.

ERSCALE = _REAL (Read and Write)
Scale the error ellipses as described above. If the command WORLD DATA (which automatically sets the graph limits) is to work properly, the global parameter PONGO_ERSCALE should have been set by READF. However, if this facility is not required, it is perfectly acceptable to set ERSCALE when invoking ELLIPSES.

[The value of the global parameter PONGO_ERSCALE is used. If PONGO_ERSCALE is not defined, the default value 1.0 is used.]