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 = 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)

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