Convert polygons to topological boundaries (lines)

Usage

ms_lines(input, fields = NULL, ...)

Arguments

input

input polygons object to convert to inner lines. One of:

geo_json or character polygons;
SpatialPolygons*;
sf or sfc polygons object

fields

character vector of field names. If left as NULL (default), external (unshared) boundaries are attributed as TYPE 0 and internal (shared) boundaries are TYPE 1. Giving a field name adds an intermediate level of hierarchy at TYPE 1, with the lowest-level internal boundaries set to TYPE 2. Supplying a character vector of field names adds additional levels of hierarchy.

...

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

topological boundaries as lines, in the same class as the input

Examples


library(geojsonsf)
library(sf)

poly <- structure('{"type":"FeatureCollection",
             "features":[
             {"type":"Feature",
             "properties":{"foo": "a"},
             "geometry":{"type":"Polygon","coordinates":[[
             [102,2],[102,3],[103,3],[103,2],[102,2]
             ]]}}
             ,{"type":"Feature",
             "properties":{"foo": "a"},
             "geometry":{"type":"Polygon","coordinates":[[
             [103,3],[104,3],[104,2],[103,2],[103,3]
             ]]}},
             {"type":"Feature",
             "properties":{"foo": "b"},
             "geometry":{"type":"Polygon","coordinates":[[
             [102.5,1],[102.5,2],[103.5,2],[103.5,1],[102.5,1]
             ]]}}]}', class = c("geojson", "json"))

poly <- geojson_sf(poly)
summary(poly)
#>      foo                     geometry
#>  Length:3           POLYGON      :3  
#>  Class :character   epsg:4326    :0  
#>  Mode  :character   +proj=long...:0  
plot(poly)


out <- ms_lines(poly)
summary(out)
#>       RANK          TYPE                    geometry
#>  Min.   :0.00   Length:4           LINESTRING   :4  
#>  1st Qu.:0.00   Class :character   epsg:4326    :0  
#>  Median :0.00   Mode  :character   +proj=long...:0  
#>  Mean   :0.25                                       
#>  3rd Qu.:0.25                                       
#>  Max.   :1.00                                       
plot(out)