#### 3.25.14 contour

contour enables contour drawing for surfaces. This option is available for ‘splot‘ only. It requires grid data, see ‘grid_data‘ for more details. If contours are desired from non-grid data, dgrid3d can be used to create an appropriate grid.

Syntax:

          set contour {base | surface | both}
          unset contour
          show contour

The three options specify where to draw the contours: ‘base‘ draws the contours on the grid base where the x/ytics are placed, surface draws the contours on the surfaces themselves, and ‘both‘ draws the contours on both the base and the surface. If no option is provided, the default is ‘base‘.

See also cntrparam for the parameters that affect the drawing of contours, and clabel for control of labelling of the contours.

The surface can be switched off (see surface), giving a contour-only graph. Though it is possible to use size to enlarge the plot to fill the screen, more control over the output format can be obtained by writing the contour information to a file, and rereading it as a 2D datafile plot:

          unset surface
          set contour
          set cntrparam ...
          set table 'filename'
          splot ...
          unset table
          # contour info now in filename
          set term <whatever>
          plot 'filename'

In order to draw contours, the data should be organized as "grid data". In such a file all the points for a single y-isoline are listed, then all the points for the next y-isoline, and so on. A single blank line (a line containing no characters other than blank spaces and a carriage return and/or a line feed) separates one y-isoline from the next. See also datafile.

See also contours demo (contours.dem) and contours with user defined levels demo (discrete.dem).