density_plots: 2D density plots for normal mixture and intensity surface
In wangyuchen/sppmix: 2D Normal Mixture Models for Spatial Point Process

Create a contour plot for the intensity surface with or without realizations on it.

## S3 method for class 'intensity_surface'
plot(x, ..., pattern, contour = FALSE,
  truncate = TRUE, L = 128)

## S3 method for class 'normmix'
plot(x, xlim, ylim, contour = FALSE, truncate = FALSE,
  L = 128, ...)

`x`	Object of class `intensity_surface` or `normmix`.
`...`	Further parameters passed to `to_int_surf()`. See `to_int_surf` for details.
`pattern`	Optional spatial point pattern to add to the plot. In the class of `ppp`.
`contour`	Logical flag indicating whether to plot countour only.
`truncate`	Whether to truncate the points outside the domain, default to TRUE.
`L`	Number of grids on each coordinate.
`xlim, ylim`	Limits for the plot when `x` is a `normmix`. If missing, quantile estimation is used to find a reasonable region.

# plot normmix density
plot(demo_mix)

# plot intensity surface
plot(demo_intsurf)

pp1 <- rsppmix(demo_intsurf)
plot(demo_intsurf, pattern = pp1)  # with points