persp                  package: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 = NULL, 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 the character
          strings; expressions are not accepted.

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.

  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.

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",
           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)

