R: Determines if a point is on or left of the vector described...

on {interp} | R Documentation

## Determines if a point is on or left of the vector described by two other points.

### Description

A simple test function to determine the position of one (or more) points relative to a vector spanned by two points.

### Usage

    on(x1, y1, x2, y2, x0, y0, eps = 1e-16)
    left(x1, y1, x2, y2, x0, y0, eps = 1e-16)

### Arguments

`x1` | `x` coordinate of first point determinig the vector.
`y1` | `y` coordinate of first point determinig the vector.
`x2` | `x` coordinate of second point determinig the vector.
`y2` | `y` coordinate of second point determinig the vector.
`x0` | vector of `x` coordinates to locate relative to the vector (x_2-x_1, y_2-y_1).
`y0` | vector of `x` coordinates to locate relative to the vector (x_2-x_1, y_2-y_1).
`eps` | tolerance for checking if x_0,y_0 is on or left of (x_2-x_1, y_2-y_1), defaults to 10^{-16}.

### Value

logical vector with the results of the test.

### Author(s)

Albrecht Gebhardt <albrecht.gebhardt@aau.at>, Roger Bivand <roger.bivand@nhh.no>

### See Also

`in.convex.hull`, `on.convex.hull`.

### Examples

    y <- x <- c(0,1)
    ## should be TRUE
    on(x[1],y[1],x[2],y[2],0.5,0.5)
    ## note the default setting of eps leading to
    on(x[1],y[1],x[2],y[2],0.5,0.50000000000000001)
    ## also be TRUE

    ## should be TRUE
    left(x[1],y[1],x[2],y[2],0.5,0.6)
    ## note the default setting of eps leading to
    left(x[1],y[1],x[2],y[2],0.5,0.50000000000000001)
    ## already resulting to FALSE

[Package interp version 1.0-33 Index]