# 1.14 Three-dimensional plotting

Three-dimensional graphs may be produced by placing the modifier `3d` immediately after the `plot` command, as demonstrated by the following simple example which draws a helix:

`set key below`
`set size 8 ratio 0.6 zratio 0.6`
`set grid`
`plot 3d sin(x):cos(x) with lw 3 col hsb(x/20+0.5,0.9,0.8)`

Many plot styles take additional columns of data when used on three-dimensional plots, reading in three values for the , and coordinates of each datapoint, where previously only and coordinates were required. In the above example, the `lines` plot style is used, which takes three columns of input data when used on three-dimensional plots, as compared to two on two-dimensional plots. The descriptions of each plot style in Section 1.2 includes information on the number of columns of data required for two- and three-dimensional plots.

The example above also demonstrates that the `set size` command takes an additional aspect ratio `zratio` which affects three-dimensional plots; whereas the aspect ratio `ratio` determines the ratio of the lengths of the -axes of plots to their -axes, the aspect ratio `zratio` determines the ratio of the lengths of the -axes of plots to their -axes.

The angle from which three-dimensional plots are viewed can be set using the `set view` command. This should be followed by two angles, which can either be expressed in degrees, as dimensionless numbers, or as quantities with physical units of angle:

    set view 60,30

    set unit angle nodimensionless
    set view unit(0.1*rev),unit(2*rad)

The orientation corresponds to having the -axis horizontal, the -axis vertical, and the -axis directed into the page. The first angle supplied to the `set view` command rotates the plot in the plane, and the second angle tips the plot up in the plane containing the -axis and the normal to the user’s two-dimensional display.

The `replot` command command may be used to add additional datasets to three-dimensional plots in an entirely analogous fashion to two-dimensional plots.

- 1.14.1 Surface plotting