tmaptools (version 1.2-4)

approx_distances: Approximate distances

Description

Approximate distances between two points or across the horizontal and vertical center lines of a bounding box.

Usage

approx_distances(x, y = NULL, projection = NULL, target = "metric",
  orig = NA, to = NA, show.warnings = TRUE)

Arguments

x

object that can be coerced to a bounding box with bb, or a pair of coordinates (vector of two). In the former case, the distance across the horizontal and vertical centerlines of the bounding box are approximated. In the latter case, y is also required; the distance between points x and y is approximated.

y

a pair of coordintes, vector of two. Only required when x is also a pair of coordintes.

projection

projection code, needed in case x is a bounding box or when x and y are pairs of coordinates. See get_proj4

target

target unit, one of: "m", "km", "mi", and "ft".

orig

original unit, i.e. by which x is defined. Only needed if this information is missing from x and x is projected. Options: "m", "km", "mi", and "ft".

to

multiplier used as follows: orig * to = target. Only needed when orig or target is unknown. For instance, if target is set to "hm" (hectometer), and orig is "m", then to should be 100, meaning 1 hectometer equals 100 meters.

show.warnings

should warnings be shown?

Value

If y is specified, a list of two: unit and dist. Else, a list of three: unit, hdist (horizontal distance) and vdist (vertical distance).

References

Tennekes, M., 2018, tmap: Thematic Maps in R, Journal of Statistical Software, 84(6), 1-39, DOI

See Also

projection_units and approx_areas

Examples

# NOT RUN {
if (require(tmap)) {
    data(NLD_prov)

    # North-South and East-West distances of the Netherlands
    approx_distances(NLD_prov)

    # Distance between Maastricht and Groningen
    p_maastricht <- geocode_OSM("Maastricht")$coords
    p_groningen <- geocode_OSM("Groningen")$coords
    approx_distances(p_maastricht, p_groningen)

    # Check distances in several projections
    sapply(c("wintri", "utm31", "laea_Eur", "rd", "longlat"), function(projection) {
        p_maastricht <- geocode_OSM("Maastricht", projection = projection)$coords
        p_groningen <- geocode_OSM("Groningen", projection = projection)$coords
        approx_distances(p_maastricht, p_groningen, projection = projection)
    })
}
# }