quadPoints {gridBezier}

Calculate Points on a Bezier Curve

Description

Calculate points on a Bezier curve and/or tangents and/or normals to the curve at those points.

Usage

quadPoints(x, range = NULL)
quadTangent(x, range = NULL)
quadNormal(x, range = NULL)

Arguments

x

A "quadGrob" object.

range

The range of t values within which to calculate points (or tangents or normals). A numeric vector of length 2.

Details

The tangents and normals are 1 inch in length.

Value

All functions return a list with components x and y. For quadPoints these are locations on the curve. For quadTangent and quadNormal, these are the distances to the end points of tangent or normal line segments. All values are in inches.

Author(s)

Paul Murrell

Examples

x <- quadGrob(c(.2, .5, .8), c(.2, .8, .2),
                stepFn=function(...) seq(0, 1, length.out=10))
grid.draw(x)
pts <- quadPoints(x)
grid.circle(pts$x, pts$y, default.units="in", r=unit(.5, "mm"),
            gp=gpar(fill="black"))
tan <- quadTangent(x)
grid.segments(pts$x, pts$y, pts$x + tan$x, pts$y + tan$y,
              default.units="in", gp=gpar(col="green"))
norm <- quadNormal(x)
grid.segments(pts$x, pts$y, pts$x + norm$x, pts$y + norm$y,
              default.units="in", gp=gpar(col="red"))