ms_filter_islands: Remove small detached polygons (islands)

In ateucher/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,
  ...
)

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" gj2008 Generate output that is consistent with the pre-RFC 7946 GeoJSON spec (dating to 2008). Polygon rings are CW and holes are CCW, which is the opposite of the default RFC 7946-compatible output. This should be rarely needed, though may be useful when preparing data for D3-based data visualizations (such as plotly::plot_ly()). Default FALSE

Value

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

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)

ateucher/rmapshaper documentation built on July 8, 2024, 7:13 p.m.