distance_to_line {tigers}

Distance to Line

Description

These functions calculate the shortest distances from a set of points to a line (in Euclidean coordinates) or an arc (in angular coordinates).

dtl and dta are aliases to distance_to_line and distance_to_arc, respectively.

Usage

distance_to_line(x, y = NULL, x0, y0, x1, y1,
                 alpha = NULL, beta = NULL)
dtl(x, y = NULL, x0, y0, x1, y1, alpha = NULL, beta = NULL)
distance_to_arc(x, y = NULL, x0, y0, x1, y1, prec = 0.001)
dta(x, y = NULL, x0, y0, x1, y1, prec = 0.001)

Arguments

x, y

the coordinates of the points given in the usual way in R.

x0, y0, x1, y1

the coordinates of two points defining the line similar to segments. These are ignored if alpha and beta are given.

alpha, beta

alternatively to the previous arguments, the parameters of the line (beta is the slope).

prec

the precision of the estimated distances (see details).

Details

distance_to_line uses Euclidean geometry (see references). The coordinates can be in any units.

distance_to_arc uses distances along arcs on the (Earth) sphere. The coordinates must be in decimal degrees. The calculations are done by iterations using intervals of decreasing lengths along the arc. The iterations are stopped when the required precision is reached (see argument prec).

Value

a numeric vector giving the distances; distance_to_line returns them in the same unit than the input data; distance_to_arc returns them in kilometres (km).

Author(s)

Emmanuel Paradis

References

https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line

See Also

great_circle_line, geoTrans, geod

Examples

## distance from the topleft corner of the unity square to the diagonal:
(d <- dtl(matrix(c(1, 0), , 2), NULL, 0, 0, 1, 1))
all.equal(d, sqrt(2)/2)

## see also ?great_circle_line
x <- y <- 0:10/10
dta(x, y, 0, 0, 1, 1)