ms_filter_islands: Remove small detached polygons (islands)

In rmapshaper: Client for 'mapshaper' for 'Geospatial' Operations

Remove small detached polygons (islands)

Description

Remove small detached polygons, keeping those with a minimum area and/or a minimum number of vertices. Optionally remove null geometries.

Usage

ms_filter_islands(
  input,
  min_area = NULL,
  min_vertices = NULL,
  drop_null_geometries = TRUE,
  force_FC = TRUE,
  sys = FALSE,
  sys_mem = 8
)

Arguments

input	spatial object to filter. One of: geo_json or character polygons; geo_list polygons; SpatialPolygons*; sf or sfc polygons object
min_area	minimum area of polygons to retain. Area is calculated using planar geometry, except for the area of unprojected polygons, which is calculated using spherical geometry in units of square meters.
min_vertices	minimum number of vertices in polygons to retain.
drop_null_geometries	should features with empty geometries be dropped? Default TRUE. Ignored for SpatialPolyons*, as it is always TRUE.
force_FC	should the output be forced to be a FeatureCollection (or Spatial*DataFrame) even if there are no attributes? Default TRUE. FeatureCollections are more compatible with rgdal::readOGR and geojsonio::geojson_sp. If FALSE and there are no attributes associated with the geometries, a GeometryCollection (or Spatial object with no dataframe) will be output.
sys	Should the system mapshaper be used instead of the bundled mapshaper? Gives better performance on large files. Requires the mapshaper node package to be installed and on the PATH.
sys_mem	How much memory (in GB) should be allocated if using the system mapshaper (sys = TRUE)? Default 8. Ignored if sys = FALSE.

Value

object with only specified features retained, in the same class as the input

Examples

library(geojsonio)
library(sp)

poly <- structure("{\"type\":\"FeatureCollection\",
           \"features\":[{\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[102,2],[102,4],[104,4],[104,2],[102,2]]]}},
           {\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,2],[98,4],[101.5,4],[100,2]]]}},
           {\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,0],[100,1],[101,1],[101,0],[100,0]]]}}]}",
           class = c("json", "geo_json"))

poly <- geojson_sp(poly)
plot(poly)

out <- ms_filter_islands(poly, min_area = 12391399903)
plot(out)

rmapshaper documentation built on May 11, 2022, 1:09 a.m.