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,
        ltheta = -135, lphi = 0, shade = NA, box = TRUE, ...)

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 colattitude.
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 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 collattitude 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.
... 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 colattitude.

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)
        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") 
persp(x, y, z, theta=30, phi=30, expand=0.5, col="lightblue",
	ltheta=120, shade = 0.75)

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

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