gplot.loop {sna}

Add Loops to a Plot

Description

gplot.loop draws a "loop" at a specified location; this is used to designate self-ties in gplot.

Usage

gplot.loop(x0, y0, length = 0.1, angle = 10, width = 0.01, col = 1,
    border = 1, lty = 1, offset = 0, edge.steps = 10, radius = 1, 
    arrowhead = TRUE, xctr=0, yctr=0, ...)

Arguments

x0

a vector of x coordinates for points of origin.

y0

a vector of y coordinates for points of origin.

length

arrowhead length, in current plotting units.

angle

arrowhead angle (in degrees).

width

width for loop body, in current plotting units (can be a vector).

col

loop body color (can be a vector).

border

loop border color (can be a vector).

lty

loop border line type (can be a vector).

offset

offset for origin point (can be a vector).

edge.steps

number of steps to use in approximating curves.

radius

loop radius (can be a vector).

arrowhead

boolean; should arrowheads be used? (Can be a vector.)

xctr

x coordinate for the central location away from which loops should be oriented.

yctr

y coordinate for the central location away from which loops should be oriented.

...

additional arguments to polygon.

Details

gplot.loop is the companion to gplot.arrow; like the latter, plot elements produced by gplot.loop are drawn using polygon, and as such are scaled based on the current plotting device. By default, loops are drawn so as to encompass a circular region of radius radius, whose center is offset units from x0,y0 and at maximum distance from xctr,yctr. This is useful for functions like gplot, which need to draw loops incident to vertices of varying radii.

Value

None.

Author(s)

Carter T. Butts [e-mail]

See Also

gplot.arrow, gplot, polygon

Examples

#Plot a few polygons with loops
plot(0,0,type="n",xlim=c(-2,2),ylim=c(-2,2),asp=1)
gplot.loop(c(0,0),c(1,-1),col=c(3,2),width=0.05,length=0.4,
  offset=sqrt(2)/4,angle=20,radius=0.5,edge.steps=50,arrowhead=TRUE)
polygon(c(0.25,-0.25,-0.25,0.25,NA,0.25,-0.25,-0.25,0.25), 
    c(1.25,1.25,0.75,0.75,NA,-1.25,-1.25,-0.75,-0.75),col=c(2,3))