tmaptools (version 3.2)

bb_poly: Convert bounding box to a spatial polygon

Description

Convert bounding box to a spatial (sfc) object . Useful for plotting (see example). The function bb_earth returns a spatial polygon of the 'boundaries' of the earth, which can also be done in other projections (if a feasible solution exists).

Usage

bb_poly(x, steps = 100, stepsize = NA, projection = NULL)
bb_earth(
  projection = NULL,
  stepsize = 1,
  earth.datum = 4326,
  bbx = c(-180, -90, 180, 90),
  buffer = 1e-06
)

Value

sfc object

Arguments

x

object that can be coerced to a bounding box with bb

steps

number of intermediate points along the shortest edge of the bounding box. The number of intermediate points along the longest edge scales with the aspect ratio. These intermediate points are needed if the bounding box is plotted in another projection.

stepsize

stepsize in terms of coordinates (usually meters when the shape is projected and degrees of longlat coordinates are used). If specified, it overrules steps

projection

projection in which the coordinates of x are provided. For bb_earth, projection is the projection in which the bounding box is returned (if possible).

earth.datum

Geodetic datum to determine the earth boundary. By default EPSG 4326.

bbx

boundig box of the earth in a vector of 4 values: min longitude, max longitude, min latitude, max latitude. By default c(-180, 180, -90, 90). If for some projection, a feasible solution does not exist, it may be wise to choose a smaller bbx, e.g. c(-180, 180, -88, 88). However, this is also automatically done with the next argument, buffer.

buffer

In order to determine feasible earth bounding boxes in other projections, a buffer is used to decrease the bounding box by a small margin (default 1e-06). This value is subtracted from each the bounding box coordinates. If it still does not result in a feasible bounding box, this procedure is repeated 5 times, where each time the buffer is multiplied by 10. Set buffer=0 to disable this procedure.

Examples

if (require(tmap) && packageVersion("tmap") >= "2.0") {
    data(NLD_muni)

    current.mode <- tmap_mode("view")
    qtm(bb_poly(NLD_muni))

    # restore mode
    tmap_mode(current.mode)
}