These functions can serve as one of the arguments `panel`

,
`lower.panel`

, `upper.panel`

, `diag.panel`

passed to graphics commands like
`pairs`

or `coplot`

,
to determine what kind of plotting is done in each panel
of a multi-panel graphical display. In particular they work
with `pairs.im`

.

The functions `panel.contour`

and `panel.contour`

are suitable for the off-diagonal plots which involve
two datasets `x`

and `y`

.
They first rescale `x`

and `y`

to the unit square,
then apply kernel smoothing with bandwidth `sigma`

using `density.ppp`

.
Then `panel.contour`

draws a contour plot
while `panel.image`

draws a colour image.

The function `panel.histogram`

is suitable for the
diagonal plots which involve a single dataset `x`

.
It displays a histogram of the data.