plotHM: Plot a height map

Description

This function can be used to plot a 'height map' of a set of rectangles in a new plot, or to add it to an existing plot. The value of the heightmap at a point equals the number of rectangles that overlap at this point.

Usage

plotHM(hm, R, grid=TRUE, grid.lty=3, grid.col="lightgray", 
       key=TRUE, n.key=10, cex.key=0.6, numbers=FALSE, 
       col=terrain.colors(max(hm)+1), xlim=NULL, ylim=NULL, 
       xlab="", ylab="", main="", sub="")

Value

No value is returned.

Arguments

hm: A (2n+1)x(2n+1) matrix with the values of the heightmap, outputted by the function reduc.
R: A nx4 matrix with the real or canonical observation rectangles. Each row corresponds to a rectangle, represented as (x1,x2,y1,y2). The point (x1,y1) is the lower left corner of the rectangle and the point (x2,y2) is the upper right corner of the rectangle.
grid: Logical, indicating if a grid should be drawn. The default value is TRUE.
grid.lty: Line type of the grid lines. The default value is 3=dotted.
grid.col: Color of the grid lines. The default value is light gray.
key: Logical, indicating if a color key should be drawn in the right margin of the plot. The default value is TRUE.
n.key: Approximate number of tickmarks for the color key. The default value is 10.
cex.key: Numerical value giving the amount by which text in the key should be scaled relative to the default. The default value is 0.6.
numbers: Logical, indicating if numbers should be plotted in the grid cells that indicate the values of the height map.
col: Color vector used to represent the values of the height map. The length of col must equal max(hm)+1.
xlim: Range for the plotted x values, defaulting to c(min(x-coordinates)-1, max(x-coordinates)+1).
ylim: Range for the plotted y values, defaulting to c(min(x-coordinates)-1, max(x-coordinates)+1).
xlab, ylab: Labels of the x and y axis. The default values are empty.
main: Title of the plot. Default value is empty.
sub: Sub title of the plot. Default value is empty.

Author

Marloes Maathuis: maathuis@stat.math.ethz.ch

Details

We chose to create a thin color key that fits in the margin of the plot. In this way, the plotting margins and plotting region do not have to be adjusted, so that other elements can be easily added to the plot later on (like observation rectangles or maximal intersections).

Examples

Run this code

# Load example data
data(ex)

# Perform reduction step
res <- reduc(ex, hm=TRUE)

# Plot the height map:
par(mfrow=c(1,1))
plotHM(res$hm, ex, main="Height map")

# Add observation rectangles in black:
plotRects(ex, add=TRUE, border="black")

# Add shaded maximal intersections:
plotRects(res$rects, add=TRUE, border=NA, density=15)

# Compute heightmap of the canonical rectangles:
canon <- real2canon(ex)
res2 <- reduc(canon, hm=TRUE)
# Note that res$hm and res2$hm are identical. So we only need to change
# the x- and y-coordinates of the height map.

# Plot height map of the canonical rectangles
plotHM(res$hm, canon, key=FALSE, numbers=TRUE, main="Canonical height map")

# Add canonical rectangles in black:
plotRects(canon, add=TRUE, border="black")

# Add canonical maximal intersections (local maxima of height map) in red:
plotRects(res2$rects, add=TRUE, border="red")

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