cp_value {cpr}

Control Polygon Value

Description

Find the y value of a Control Polygon for a given x

Usage

cp_value(obj, x)

Arguments

obj

a cpr_cp object or data.frame where the first column is the abscissa and the second column is the ordinate for the control polygon vertices.

x

abscissa at which to determine the ordinate on control polygon cp

Value

cp_value returns the ordinate on the control polygon line segment for the abscissa x given. x could be a control vertex or on a line segment defined by two control vertices of the control polygon provided.

cp_diff returns the vertical distance between the control vertices of cp1 to the control polygon cp2.

See Also

cp, cp_diff

Examples

xvec <- seq(0, 6, length = 500)

# Define the basis matrix
bmat1 <- bsplines(x = xvec, iknots = c(1, 1.5, 2.3, 4, 4.5))
bmat2 <- bsplines(x = xvec)

# Define the control vertices ordinates
theta1 <- c(1, 0, 3.5, 4.2, 3.7, -0.5, -0.7, 2, 1.5)
theta2 <- c(1, 3.4, -2, 1.7)

# build the two control polygons
cp1 <- cp(bmat1, theta1)
cp2 <- cp(bmat2, theta2)

x <- c(0.2, 0.8, 1.3, 1.73, 2.15, 3.14, 4.22, 4.88, 5.3, 5.9)
cp_value(cp1, x = x)

df <- data.frame(x = x, y = cp_value(cp1, x = x))

plot(cp1, show_x = TRUE, show_spline = TRUE) +
ggplot2::geom_point(data = df
  , mapping = ggplot2::aes(x = x, y = y)
  , color = "red"
  , shape = 4
  , size = 3
  , inherit.aes = FALSE)