R: Perspective Plots

persp {base}

R Documentation

Perspective Plots

Description

This function draws perspective plots of surfaces over the x–y plane. persp is a generic function.

Usage

persp(x, ...)
persp.default(x = seq(0, 1, len = nrow(z)), y = seq(0, 1, len = ncol(z)), z,
      xlim = range(x), ylim = range(y), zlim = range(z, na.rm = TRUE), 
      xlab = NULL, ylab = NULL, zlab = NULL, main = NULL, sub = NULL,
      theta = 0, phi = 15, r = sqrt(3), d = 1, scale = TRUE, expand = 1, 
      col = "white", border = NULL, ltheta = -135, lphi = 0, shade = NA,
      box = TRUE, axes = TRUE, nticks = 5, ticktype = "simple",
      ...)

Arguments

`x`, `y`	locations of grid lines at which the values in `z` are measured. These must be in ascending order. By default, equally spaced values from 0 to 1 are used. If `x` is a `list`, its components `x$x` and `x$y` are used for `x` and `y`, respectively.
`z`	a matrix containing the values to be plotted (`NA`s are allowed). Note that `x` can be used instead of `z` for convenience.
`xlim`, `ylim`, `zlim`	x-, y- and z-limits. The plot is produced so that the rectangular volume defined by these limits is visible.
`xlab`, `ylab`, `zlab`	titles for the axes. N.B. These must be character strings; expressions are not accepted. Numbers will be coerced to character strings.
`main`, `sub`	main and sub title, as for `title`.
`theta`, `phi`	angles defining the viewing direction. `theta` gives the azimuthal direction and `phi` the colatitude.
`r`	the distance of the eyepoint from the centre of the plotting box.
`d`	a value which can be used to vary the strength of the perspective transformation. Values of `d` greater than 1 will lessen the perspective effect and values less and 1 will exaggerate it.
`scale`	before viewing the x, y and z coordinates of the points defining the surface are transformed to the interval [0,1]. If `scale` is `TRUE` the x, y and z coordinates are transformed separately. If `scale` is `FALSE` the coordinates are scaled so that aspect ratios are retained. This is useful for rendering things like DEM information.
`expand`	a expansion factor applied to the `z` coordinates. Often used with `0 < expand < 1` to shrink the plotting box in the `z` direction.
`col`	the color of the surface facets. Transparent colours are ignored.
`border`	the color of the line drawn around the surface facets. A value of `NA` will disable the drawing of borders. This is sometimes useful when the surface is shaded.
`ltheta`, `lphi`	if finite values are specified for `ltheta` and `lphi`, the surface is shaded as though it was being illuminated from the direction specified by azimuth `ltheta` and colatitude `lphi`.
`shade`	the shade at a surface facet is computed as `((1+d)/2)^shade`, where `d` is the dot product of a unit vector normal to the facet and a unit vector in the direction of a light source. Values of `shade` close to one yield shading similar to a point light source model and values close to zero produce no shading. Values in the range 0.5 to 0.75 provide an approximation to daylight illumination.
`box`	should the bounding box for the surface be displayed. The default is `TRUE`.
`axes`	should ticks and labels be added to the box. The default is `TRUE`. If `box` is `FALSE` then no ticks or labels are drawn.
`ticktype`	character: "simple" draws just an arrow parallel to the axis to indicate direction of increase; "detailed" draws normal ticks as per 2D plots.
`nticks`	the (approximate) number of tick marks to draw on the axes. Has no effect if `ticktype` is "simple".
`...`	additional graphical parameters (see `par`).

Details

The plots are produced by first transforming the coordinates to the interval [0,1]. The surface is then viewed by looking at the origin from a direction defined by theta and phi. If theta and phi are both zero the viewing direction is directly down the negative y axis. Changing theta will vary the azimuth and changing phi the colatitude.

Examples

# (1) The Obligatory Mathematical surface.
#     Rotated sinc function.

x <- seq(-10, 10, length=50)
y <- x
f <- function(x,y)
{
    r <- sqrt(x^2+y^2)
    10 * sin(r)/r
}
z <- outer(x, y, f)
z[is.na(z)] <- 1
par(bg = "white")
persp(x, y, z, theta = 30, phi = 30, expand = 0.5, col = "lightblue",
      xlab = "X", ylab = "Y", zlab = "Z") 
persp(x, y, z, theta = 30, phi = 30, expand = 0.5, col = "lightblue",
      ltheta = 120, shade = 0.75, ticktype = "detailed",
      xlab = "X", ylab = "Y", zlab = "Z") 


# (2) Visualizing a simple DEM model

data(volcano)
z <- 2 * volcano        # Exaggerate the relief
x <- 10 * (1:nrow(z))   # 10 meter spacing (S to N)
y <- 10 * (1:ncol(z))   # 10 meter spacing (E to W)
persp(x, y, z, theta = 120, phi = 15, scale = FALSE, axes = FALSE)


# (3) Now something more complex
#     We border the surface, to make it more "slice like"
#     and color the top and sides of the surface differently.

zmin <- min(z) - 20
z <- rbind(zmin, cbind(zmin, z, zmin), zmin)
x <- c(min(x) - 1e-10, x, max(x) + 1e-10)
y <- c(min(y) - 1e-10, y, max(y) + 1e-10)

fill <- matrix("green3", nr = nrow(z)-1, nc = ncol(z)-1)
fill[,1] <- "gray"
fill[,ncol(fill)] <- "gray"
fill[1,] <- "gray"
fill[nrow(fill),] <- "gray"

par(bg = "lightblue")
persp(x, y, z, theta = 120, phi = 15, col = fill, scale = FALSE, axes = FALSE)
title(main = "Maunga Whau\nOne of 50 Volcanoes in the Auckland Region.",
      font.main = 4)

par(bg = "slategray")
persp(x, y, z, theta = 135, phi = 30, col = fill, scale = FALSE,
      ltheta = -120, lphi = 15, shade = 0.65, axes = FALSE)
persp(x, y, z, theta = 135, phi = 30, col = "green3", scale = FALSE,
      ltheta = -120, shade = 0.75, border = NA, box = FALSE)