Draw an arc showing the angle between vectors

A utility function for drawing vector diagrams. Draws a circular arc to show the angle between two vectors in 2D or 3D.

Usage

arc(p1, p2, p3, d = 0.1, absolute = TRUE, ...)

Arguments

p1

Starting point of first vector

p2

End point of first vector, and also start of second vector

p3

End point of second vector

d

The distance from p2 along each vector for drawing their corner

absolute

logical; if TRUE, d is taken as an absolute distance along the vectors; otherwise it is calculated as a relative distance, i.e., a fraction of the length of the vectors.

...

Arguments passed to lines or to lines3d

Value

none

Details

In this implementation, the two vectors are specified by three points, p1, p2, p3, meaning a line from p1 to p2, and another line from p2 to p3.

References

https://math.stackexchange.com/questions/1507248/find-arc-between-two-tips-of-vectors-in-3d

See also

Other vector diagrams: Proj(), arrows3d(), circle3d(), corner(), plot.regvec3d(), pointOnLine(), regvec3d(), vectors(), vectors3d()

Examples

library(rgl)
#> 
#> Attaching package: 'rgl'
#> The following object is masked from 'package:matlib':
#> 
#>     GramSchmidt
vec <- rbind(diag(3), c(1,1,1))
rownames(vec) <- c("X", "Y", "Z", "J")
open3d()
aspect3d("iso")
vectors3d(vec, col=c(rep("black",3), "red"), lwd=2)
# draw the XZ plane, whose equation is Y=0
planes3d(0, 0, 1, 0, col="gray", alpha=0.2)
# show projections of the unit vector J
segments3d(rbind( c(1,1,1), c(1, 1, 0)))
segments3d(rbind( c(0,0,0), c(1, 1, 0)))
segments3d(rbind( c(1,0,0), c(1, 1, 0)))
segments3d(rbind( c(0,1,0), c(1, 1, 0)))
segments3d(rbind( c(1,1,1), c(1, 0, 0)))

# show some orthogonal vectors
p1 <- c(0,0,0)
p2 <- c(1,1,0)
p3 <- c(1,1,1)
p4 <- c(1,0,0)
# show some angles
arc(p1, p2, p3, d=.2)
arc(p4, p1, p2, d=.2)
arc(p3, p1, p2, d=.2)