rmapshaper (version 0.5.0)

ms_filter_islands: 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,
  ...
)

Value

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

Arguments

input

spatial object to filter. One of:

• geo_json or character 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.

...

Arguments passed on to apply_mapshaper_commands

force_FC

should the output be forced to be a FeatureCollection (or sf object or Spatial*DataFrame) even if there are no attributes? Default TRUE. If FALSE and there are no attributes associated with the geometries, a GeometryCollection (or Spatial object with no dataframe, or sfc) 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. This can also be set globally with the option "mapshaper.sys_mem"

quiet

If sys = TRUE, should the mapshaper messages be silenced? Default FALSE. This can also be set globally with the option "mapshaper.sys_quiet"

Examples

library(geojsonsf)
library(sf)

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("geojson", "json"))

poly <- geojson_sf(poly)
plot(poly)

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