transformations: Transform Point Array

Description

Flip (reflect), rotate or slide (translate) an array of points. Methods are provided for `traps' objects that ensure other attributes are retained. The methods may be used with rbind.traps to create complex geometries.

Usage

flip (object, lr = FALSE, tb = FALSE, ...)
rotate (object, degrees, centrexy = NULL, ...)
shift (object, shiftxy, ...)
# S3 method for traps
flip (object, lr = FALSE, tb = FALSE, ...)
# S3 method for traps
rotate(object, degrees, centrexy = NULL, ...)
# S3 method for traps
shift(object, shiftxy, ...)
# S3 method for popn
flip (object, lr = FALSE, tb = FALSE, ...)
# S3 method for popn
rotate(object, degrees, centrexy = NULL, ...)
# S3 method for popn
shift(object, shiftxy, ...)
# S3 method for mask
shift(object, shiftxy, ...)

Value

A matrix or object of class `traps' or `popn' with the coordinates of each point transformed as requested.

Arguments

object: a 2-column matrix or object that can be coerced to a matrix
lr: either logical for whether array should be flipped left-right, or numeric value for x-coordinate of axis about which it should be flipped left-right
tb: either logical for whether array should be flipped top-bottom, or numeric value for y-coordinate of axis about which it should be flipped top-bottom
degrees: clockwise angle of rotation in degrees
centrexy: vector with xy coordinates of rotation centre
shiftxy: vector of x and y displacements
...: other arguments (not used)

Details

flip reflects points about a vertical or horizontal axis. Logical values for lr or tb indicate that points should be flipped about the mean on the relevant axis. Numeric values indicate the particular axis value(s) about which points should be flipped. The default arguments result in no change.

shift shifts the location of each point by the desired amount on each axis.

rotate rotates the array about a designated point. If centrexy is NULL then rotation is about (0,0) (rotate.default), the array centre (rotate.traps), or the centre of the bounding box (rotate.popn).

Examples

Run this code


temp <- matrix(runif (20) * 2 - 1, nc = 2)

## flip
temp2 <- flip(temp, lr = 1)
plot(temp, xlim=c(-1.5,4), ylim = c(-1.5,1.5), pch = 16)
points (temp2, pch = 1)
arrows (temp[,1], temp[,2], temp2[,1], temp2[,2], length = 0.1)
abline(v = 1, lty = 2)

## rotate
temp2 <- rotate(temp, 25)
plot(temp, xlim=c(-1.5,1.5), ylim = c(-1.5,1.5), pch = 16)
points (0,0, pch=2)
points (temp2, pch = 1)
arrows (temp[,1], temp[,2], temp2[,1], temp2[,2], length = 0.1)	

## shiftxy
temp2 <- shift(temp, c(0.1, 0.1))
plot(temp, xlim=c(-1.5,1.5), ylim = c(-1.5,1.5), pch = 16)
points (0,0, pch=2)
points (temp2, pch = 1)
arrows (temp[,1], temp[,2], temp2[,1], temp2[,2], length = 0.1)	

## flip.traps
par(mfrow = c(1,2), xpd = TRUE)
traps1 <- make.grid(nx = 8, ny = 6, ID = "numxb")
traps2 <- flip (traps1, lr = TRUE)
plot(traps1, border = 5, label = TRUE, offset = 7, gridl = FALSE)
plot(traps2, border = 5, label = TRUE, offset = 7, gridl = FALSE)
par(mfrow = c(1,1), xpd = FALSE)

## rotate.traps
hollow1 <- make.grid(nx = 8, ny = 8, hollow = TRUE)
nested <- rbind (hollow1, rotate(hollow1, 45, c(70, 70)))
plot(nested, gridlines = FALSE)

## shift.traps
hollow1 <- make.grid(nx = 8, ny = 8, hollow = TRUE)
hollow2 <- shift(make.grid(nx = 6, ny = 6, hollow = TRUE), c(20, 20))
nested <- rbind (hollow1, hollow2)
plot(nested, gridlines = FALSE, label = TRUE)