Area for each polygon in JamPolygon

Area for each polygon in JamPolygon

area_JamPolygon(
  jp,
  apply_abs = FALSE,
  flip_sign = 1,
  return_list = FALSE,
  verbose = FALSE,
  ...
)

Arguments

jp

JamPolygon

apply_abs

logical (default FALSE) indicating whether to use the absolute value of the area prior to applying the orientation.

• When FALSE, it uses the orientation of the points, where clockwise indicates positive, and counter-clockwise indicates negative.

• When TRUE it calculates absolute area, and flips the sign based upon the orientation from add_orientation_JamPolygon(), which itself defines orientation based upon (1) the clockwise nature of points, and (2) whether the polygon is inside a parent polygon.

flip_sign

integer indicating whether to flip the sign of the orientation, and is passed to add_orientation_JamPolygon().

return_list

logical indicating whether to return a list with area of each polygon part, one numeric vector per row in jp@polygons. Note that this step does not indicate which polygon hole is encompassed inside another larger polygon, so it cannot directly be used to determine the largest polygon in complex nested polygon structures.

...

additional arguments are ignored.

Value

numeric vector with the area of each polygon, one value per row in jp@polygons. Or when return_list=TRUE a list where each element is produced per row of jp@polygons, containing a numeric vector with the area of each polygon part. Note that holes are represented with negative area multiplied by the orientation of the parent encompassing polygon.

Details

This function calculates the area of each individual polygon (row) represented in a JamPolygon object. It calculates total area of multi-part polygons, which by default calculates the positive area of polygons, and subtracts area for any holes. The orientation defines the presence of holes using add_orientation_JamPolygon().

For example, it is possible to have three concentric circles as a three-part polygon. By convention, the first polygon defines the outer border, the second polygon defines an inner border hole), and the third polygon defines a nested internal polygon.

Todo:

• Consider simplifying polygons beforehand, to guarantee that no multi-part polygons contain overlapping sections. Currently this function assumes the input polygons are already simplified, such that multi-part polygons on one row of jp@polygons do not contain partially overlapping polygons, instead polygons are either adjacent, fully overlapping (holes), or fully disconnected.

See also

Other JamPolygon: JamPolygon-class, Venndir-class, [,JamPolygon,ANY,ANY,ANY-method, add_orientation_JamPolygon(), bbox_JamPolygon(), buffer_JamPolygon(), check_JamPolygon(), check_Venndir(), eulerr_to_JamPolygon(), farthest_point_JamPolygon(), find_venn_overlaps_JamPolygon(), has_point_in_JamPolygon(), intersect_JamPolygon(), label_fill_JamPolygon(), label_outside_JamPolygon(), label_segment_JamPolygon(), labelr_JamPolygon(), minus_JamPolygon(), nearest_point_JamPolygon(), nudge_JamPolygon(), plot.JamPolygon(), point_in_JamPolygon(), polyclip_to_JamPolygon(), polygon_circles(), polygon_ellipses(), sample_JamPolygon(), split_JamPolygon(), union_JamPolygon(), update_JamPolygon()

Examples

df3 <- data.frame(name=c("polygon1", "polygon2"),
   label=c("polygon1", "polygon2"),
   x=I(list(
      list(c(1, 6, 6, 1),
         c(2, 5, 5, 2),
         c(3, 4, 4, 3)),
      list(#c(11, 16, 16, 11),
         c(12, 15, 15, 12),
         c(13, 14, 14, 13))
      )),
   y=I(list(
      list(c(1, 1, 6, 6),
         c(2, 2, 5, 5),
         c(3, 3, 4, 4)),
      list(#c(1, 1, 6, 6),
         c(2, 2, 5, 5),
         c(3, 3, 4, 4))
      )),
   fill=c("gold", "firebrick"))
jp3 <- new("JamPolygon", polygons=df3);
plot(jp3);


area_JamPolygon(jp3)
#> [1] 17  8

jp3@polygons$label <- paste0(names(jp3),
   "\narea=", area_JamPolygon(jp3));
plot(jp3)


area_JamPolygon(jp3, return_list=TRUE)
#> [[1]]
#> [1] 25 -9  1
#> 
#> [[2]]
#> [1]  9 -1
#>