These functions provide a simple formula-based interface
to `plot3d`

and `persp3d`

.

```
# S3 method for formula
plot3d(x, data = NULL, xlab, ylab, zlab, ...)
# S3 method for formula
persp3d(x, data = NULL, xlab, ylab, zlab, ...)
```

## Arguments

- x
A formula like `z ~ x + y`

.

- data
An optional dataframe or list in which to find the components
of the formula.

- xlab, ylab, zlab
Optional axis labels to override the ones automatically
obtained from the formula.

- ...
Additional arguments to pass to the default `plot3d`

method, or the `persp3d`

method for `"deldir"`

objects.

## Details

Only simple formulas (the ones handled by the `xyz.coords`

function) are supported: a single variable on the left hand side (which will be plotted on the Z axis),
and a sum of two variables on the right hand side (which
will be the X and Y axis variables in the plot.)

## Note

The `persp3d`

method requires that the suggested package deldir is installed.

## Value

These functions are called for the side effect of drawing
the plots. The `plot3d`

method draws a scatterplot. The `persp3d`

method draws a surface plot.

Return values are as given by the `plot3d.default`

method or the `persp3d.deldir`

methods.