Default and Custom Arrows Added to a Plot
# 15.3c Arrows =========================================================== 15.3c
# A solid arrowhead function
#
# This function draws an arrow from (x0,y0) to (x1,y1) with a solid
# arrowhead.
#
# The default arrowhead length is .25 inches.
# The default angle of the arrowhead edges is 30 degrees.
# The other parameters are standard for line and polygon formatting.
#
# The basic logic here is to use matrix rotation to translate the arrowhead
# coordinates.
#
# Note that R's trigonometric functions work with radians rather than degrees
#
myArrow = function(x0, y0, x1, y1, # Set up arrow function ----------------+
L = .25, # Default arrowhead length |
angle = 30, # Default angle of arrowhead |
code = 2, # Default arrowhead at x1,y1 |
col = par("fg"), # Default color |
ljoin = par("ljoin"), # Default line joint style (0) |
lty = par("lty"), # Default line type |
lwd = par("lwd"), # Default line width |
xpd = FALSE){ # Default stay within plot area |
# Start function code |
if(code == 1){ # Reverse arrow direction |
tmp = x1; x1 = x0; x0 = tmp # Switch x values |
} # |
if(code == 1){ # |
tmp = y1; y1 = y0; y0 = tmp # Switch y values |
} # |
# |
# We need to control for the aspect ratio or for different x,y scales |
# in setting up the arrow heads. We'll do that by translating the |
# usr parameter setting from the original x,y units to units based |
# on the plot dimensions measured in inches. This will allow us to |
# adjust the angles to account for different x and y scales. Note, |
# however, that rescaling the plot after it is drawn will distort |
# the arrowheads. |
# |
X0 = (x0 - par()$usr[1])/(par()$usr[2] - par()$usr[1]) * par()$fin[1] # |
Y0 = (y0 - par()$usr[3])/(par()$usr[4] - par()$usr[3]) * par()$fin[2] # |
X1 = (x1 - par()$usr[1])/(par()$usr[2] - par()$usr[1]) * par()$fin[1] # |
Y1 = (y1 - par()$usr[3])/(par()$usr[4] - par()$usr[3]) * par()$fin[2] # |
# |
oldusr = par("usr") # Save original usr settings |
par(usr = c(0, par("fin")[1], # Set up new usr settings based |
0, par("fin")[2])) # on plot dimensions in inches |
# |
t = angle * pi/180 # Convert angle degrees to radians |
slope = (Y1 - Y0)/(X1 - X0) # Calculate slope of line |
S = atan(slope) # Slope angle in radians |
# |
M = ifelse(X1 < X0, -1, 1) # Set a marker for X1 < X0 |
# Set length of vector XA |
XA = sqrt((X1 - X0)^2 + (Y1 - Y0)^2) # |
# |
# Get arrowhead vertices from rotated vectors |
XC = X0 + M * ((XA - L) * cos(S) + L * tan(t) * sin(S)) # |
YC = Y0 + M * ((XA - L) * sin(S) - L * tan(t) * cos(S)) # |
XB = X0 + M * ((XA - L) * cos(S) - L * tan(t) * sin(S)) # |
YB = Y0 + M * ((XA - L) * sin(S) + L * tan(t) * cos(S)) # |
# | |
# Draw arrow line stopping at beginning of the arrowhead |
lines(x = c(X0, X1 - M * L * cos(S)), # |
y = c(Y0, Y1 - M * L * sin(S)), # |
lty = lty, lwd = lwd, # Apply line format options |
col = col, xpd = xpd, # |
ljoin = ljoin) # |
polygon(x = c(X1, XB, XC), # Draw arrow head |
y = c(Y1, YB, YC), # at vertices |
col = col, # Apply format options |
border = col, # |
xpd = xpd) # |
par(usr = oldusr) # Reset to original usr settings |
} # End of myArrow function --------------+
# A plot of arrows
png(filename = "illustrations/fig-15-10-arrows-BW.png",
units = "in", # Set measurements in inches
res = 1200, # Set resolution at 1200dpi
width = 6, # Width at 6 inches
height = 4) # Height at 4 inches
par(mai = c(.5, .5, .25, .25)) # Set margin widths in lines
plot(x = 0, y = 0, type = "n", # Set up a blank plot
xlim = c(0, 5), ylim = c(0, 5), # Define x and y range
xlab = "", ylab = "") # Turn off axis labels
# Diverse arrows
arrows(x0 = 3, y0 = 4.25, x1 = 5, y1 = .25,
length = 1, angle = 15, lwd = 2)
arrows(x0 = 1.25, y0 = 1, x1 = 3.25, y1 = .75,
col = "darkgray", code = 3)
myArrow(x0 = 0, y0 = 1.5, x1 = 3.5, y1 = 4.5,
col = "black")
myArrow(x0 = 1, y0 = .5, x1 = 4.5, y1 = 0,
col = gray(.6))
myArrow(x0 = 4, y0 = 3.5, x1 = 1, y1 = 1.5, L=.5,
col = gray(.4), lwd = 2)
myArrow(x0 = 2.5, y0 = 1.25, x1 = 1, y1 = 4.2,
col = gray(.5), lwd = 4)
myArrow(x0 = 6, y0 = 5, x1 = 4, y1 = 3,
col = "gray", lwd = 8, angle = 20, L=.75, xpd = T)
myArrow(x0 = 0, y0 = 5, x1 = 4, y1 = 5,
col = "gray", lwd = 3, angle = 40, code = 1)
myArrow(x0 = .5, y0 = .5, x1 = 4, y1 = 1.5,
col = "darkgray", lwd = 1, angle = 20, L=.1)
dev.off() # Output png file