Create points from a polygon layer — ms

Can be generated from the polygons by specifying location to be "centroid" or "inner", OR by specifying fields in the attributes of the layer containing x and y coordinates.

Usage

ms_points(input, location = NULL, x = NULL, y = NULL, ...)

Arguments

input

input polygons object to convert to points. One of:

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

location

either "centroid" or "inner". If "centroid", creates points at the centroid of the largest ring of each polygon feature. if "inner", creates points in the interior of the largest ring of each polygon feature. Inner points are located away from polygon boundaries. Must be NULL if x and y are specified. If left as NULL (default), will use centroids.

x

name of field containing x coordinate values. Must be NULL if location is specified.

y

name of field containing y coordinate values. Must be NULL if location is specified.

...

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

points in the same class as the input.

Examples

library(geojsonsf)
library(sf)

poly <- structure("{\"type\":\"FeatureCollection\",
           \"features\":[{\"type\":\"Feature\",\"properties\":
           {\"x_pos\": 1, \"y_pos\": 2},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[102,2],[102,4],[104,4],[104,2],[102,2]]]}},
           {\"type\":\"Feature\",\"properties\":{\"x_pos\": 3, \"y_pos\": 4},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,2],[98,4],[101.5,4],[100,2]]]}},
           {\"type\":\"Feature\",\"properties\":{\"x_pos\": 5, \"y_pos\": 6},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,0],[100,1],[101,1],[101,0],[100,0]]]}}]}",
           class = c("geojson", "json"))

poly <- geojson_sf(poly)
summary(poly)
#>      x_pos       y_pos            geometry
#>  Min.   :1   Min.   :2   POLYGON      :3  
#>  1st Qu.:2   1st Qu.:3   epsg:4326    :0  
#>  Median :3   Median :4   +proj=long...:0  
#>  Mean   :3   Mean   :4                    
#>  3rd Qu.:4   3rd Qu.:5                    
#>  Max.   :5   Max.   :6                    
plot(poly)


# Convert to points using centroids
out <- ms_points(poly, location = "centroid")
summary(out)
#>      x_pos       y_pos            geometry
#>  Min.   :1   Min.   :2   POINT        :3  
#>  1st Qu.:2   1st Qu.:3   epsg:4326    :0  
#>  Median :3   Median :4   +proj=long...:0  
#>  Mean   :3   Mean   :4                    
#>  3rd Qu.:4   3rd Qu.:5                    
#>  Max.   :5   Max.   :6                    
plot(out)


# Can also specify locations using attributes in the data
out <- ms_points(poly, x = "x_pos", y = "y_pos")
summary(out)
#>      x_pos       y_pos            geometry
#>  Min.   :1   Min.   :2   POINT        :3  
#>  1st Qu.:2   1st Qu.:3   epsg:4326    :0  
#>  Median :3   Median :4   +proj=long...:0  
#>  Mean   :3   Mean   :4                    
#>  3rd Qu.:4   3rd Qu.:5                    
#>  Max.   :5   Max.   :6                    
plot(out)