Three-Dimensional Perspective Plots

DESCRIPTION:

USAGE:

persp(x, y, z, xlab = "X", ylab = "Y", zlab = "Z", axes = T,  
      box = T, eye = <<see below>>, zlim = <<see below>>, ar = 1) 

REQUIRED ARGUMENTS:

x

vector containing x coordinates of the grid over which z is evaluated. The values should be in sorted order; missing values are not accepted.

y

vector of grid y coordinates. The values should be in sorted order; missing values are not accepted.

z

matrix of size length(x) by length(y) giving the surface height at grid points, i.e., z[i,j] is evaluated at x[i], y[j]. The rows of z are indexed by x, and the columns by y. Missing values ( NAs) are allowed, but should generally not occur in the convex hull of the non-missing values.

The first argument may be a list with components x, y, and z. In particular, the result of interp is suitable.

If the first argument is a matrix, it is assumed to be the z matrix and vectors x and y are generated ( x is 1:nrow(z), y is 1:ncol(z)). The result of predict together with expand.grid is suitable as an argument to persp.

OPTIONAL ARGUMENTS:

xlab

character label for the x axis.

ylab

character label for the y axis.

zlab

character label for the z axis.

eye

vector giving the x,y,z coordinates for the viewpoint. The default is c(-6, -8, 5) times the range of the x, y, and z values.

axes

logical flag: should axes be drawn around the surface?

box

logical flag: should a box be drawn around the surface?

zlim

vector of the desired minimum and maximum z axis values. The default is the range(z, na.rm=T). This range will be expanded to round numbers. The values in the input matrix z will be truncated to the z axis limits.

ar

aspect ratio for plotting the x,y grid, i.e., (xmax-xmin)/(ymax-ymin)" .

Graphical parameters may also be supplied as arguments to this function (see par ).

NOTE:

persp assumes that the grid vectors x and y are increasing and evenly spaced. If this is not true, suppress the axes with axes=F or use par commands to customize the axes.

VALUE:

invisible list containing information about what was plotted.

rotation

integer flag between 1 and 4 describing the point of view based on which corner of the xy plane appears closest to the viewer.

proj

2 by 2 by 2 array describing the projection of vectors that span the data.

rangex

vector giving the min and max values for x.

rangey

vector giving the min and max values for y.

rangez

vector giving the min and max values for z.

SIDE EFFECTS:

DETAILS:

Use persp.setup to change the color, line width and line type of the perspective lines. Use the perspp function to add information to a perspective plot.

BUGS:

For some plots (including the case where mfrow or mfcol is bigger than c(2,2)) parts of the axes are cut off. You can solve this problem either by putting up fewer figures on the page, changing the perspective angle with the eye argument, or by expanding the margin in which the cut off occurs.

Lines with an endpoint outside the plot may not be drawn.

SEE ALSO:

EXAMPLES:

#Example 1, a polynomial 
poly1 <-function(x, y){ 
        x^2 + x * y + y^2       } 
y <- x <- seq(-25, 25, length = 50) 
persp(x,y, outer(x,y, FUN =  poly1)) 
#Example 2, data at geographic points 
i <- interp(ozone.xy$x,ozone.xy$y,ozone.median) 
persp(i, xlab = "Longitude", ylab = "Latitude", zlab = "Ozone") 
title(main = "Median Ozone Concentrations in the North East") 
#Example 3, first argument is a matrix 
persp(switzerland) 
#Example 4, a smooth surface 
int.ak <- interp(akima.x, akima.y, akima.z) 
r.ak <- sapply(int.ak, function(x) diff(range(x,na.rm = T))) 
par(mfrow = c(2,2), oma = c(0,0,5,0)) 
persp(int.ak) 
persp(int.ak, eye = c(6,-8,5)*r.ak) 
persp(int.ak, eye = c(6,8,5)*r.ak) 
persp(int.ak, eye = c(-6,8,5)*r.ak) 
mtext(outer = T, side = 3, line = 2, "WAVEFORM DISTORTION",  
      cex = 1.5) 
par(mfrow = c(1,1)) 
persp(int.ak, eye = c(6,8,5)*r.ak) 
title(main = "WAVEFORM DISTORTION")