Perspective Plots

Usage

persp(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=T),
        theta = 0, phi = 15, d = 1, scale = TRUE, col, border, ...)

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 (NAs 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.
theta, phi angles defining the viewing direction. theta gives the azimuthal direction and phi the elevation.
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.
col the color of the surface facets.
border color of the line drawn around the surface facets.
... additional graphical parameters (see par) and the arguments to title may also be supplied.

Description

This function draws perspective plots of surfaces over the x-y plane. 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 elevation.

See Also

contour and image.

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)
        sin(r)/r
}
z <- outer(x,y,f)
z[is.na(z)] <- 1
persp(x, y, z, theta=30, phi=30, expand=0.5, col="lightblue")

# (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)

# (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("green2", 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=F)
title(main="Maunga Whau\nOne of 50 Volcanoes in the Auckland Region.",
font.main=4)


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