Calculate triangle area from a matrix of coordinates. Triangles are composed
of three coordinates, so the matrix should have this as triplets of rows
one after the other.
Usage
triangle_area(x, signed = FALSE)
Value
numeric vector of area
Arguments
x
coordinates x,y triplets matrix where 'nrow(x) = ntriangles*3'
signed
defaults to FALSE and absolute value of area is returned,
if TRUE negative means clockwise 'p->q->r' turns right and positive means
counter-clockwise 'p->q->r' turns left
Details
If signed = FALSE the absolute value of area is returned, otherwise the
sign reflects path orientation. Positive means counter-clockwise orientation.
The algorithm was once documented at 'w w w cs.tufts.edu/comp/163/OrientationTests.pdf'