Contour level selection

Syntax: | `CONTOUR { x y } v nctr { min { incr }} CONTOUR\SPECIFIC { x y } v lvls`

By default, the number of contours, `nctr`, must be provided. If `nctr > 0` and the increment is not specified, the actual number of contours drawn may not be the same as the number that was asked for, since "nice" contour levels will be selected and the range of values may not be neatly divisible by the requested number. If the minimum is provided, but not the increment, a "nice" value close to `min` will be used instead of the actual data minimum. If the minimum and the increment are both specified, those exact values will be used for the contour levels.

Specific contour levels

Specific contour levels can be requested by using the `\SPECIFIC` qualifier. In this case, the vector `lvls` should contain the desired contour levels.

Exact contour levels

Exact contour levels can be requested in three ways.

- Use the `\SPECIFIC` qualifier and enter a vector containing the desired levels.
- Specify the minimum contour level, `min`, and the contour level increment, `inc`. This produces a set of equally spaced contour levels,
  `[min; min+inc; min+2*inc; ...; min+nctr*inc]`.
- Specify a negative number of contours, `nctr < 0`. This produces a set of equally spaced contour levels, as above, using the actual data minimum and the actual data maximum.

Zooming in

When the minimum and maximum contour levels are to be determined, by default, the entire range of the data is used. If the `\PARTIAL` qualifier is used, the minimum and maximum contour levels will be determined by the region contained within the axes. Thus, to zoom in on a particular region for more detail, pre-set the axis scales, using the `SCALES` command, before entering the `CONTOUR` command. Of course, the `\PARTIAL` qualifier does not apply when you request specific contour levels.

CONTOUR command
Contour level colour