Convert a Polygon to a Spatial Polygons Object
Converts a polygon (a matrix of coordinates with NA values to separate subpolygons) into a Spatial Polygons object.
polygon2spatial_polygon(poly, coordinate.system, area.names = NULL, nrepeats = NULL)
poly |
a 2-column matrix of coordinates, where each complete subpolygon is separated by NA's |
coordinate.system |
the coordinate system to use |
area.names |
names of all areas |
nrepeats |
number of subpolygons for each area |
Just as when plotting with the polygon function, it is assumed that each subpolygon is to be closed by joining the last point to the first point. In the matrix poly, NA values separate complete subpolygons.
coordinate.system must be either '+proj=utm' or '+proj=longlat'.
In the case with an area consists of more than one separate closed polygon,
nrepeats specifies the number of closed polygons associated with each area.
An object of class SpatialPolygons (See SpatialPolygons-class from the sp package).
Albert Y. Kim
Bivand, R. S., Pebesma E. J., and Gomez-Rubio V. (2008) Applied Spatial Data Analysis with R. Springer Series in Statistics.
E. J. Pebesma and R. S. Bivand. (2005) Classes and methods for spatial data in R. R News, 5, 9–13.
data(scotland) polygon <- scotland$polygon$polygon coord.system <- '+proj=utm' names <- scotland$data$county.names nrepeats <- scotland$polygon$nrepeats spatial.polygon <- polygon2spatial_polygon(polygon,coord.system,names,nrepeats) par(mfrow=c(1,2)) # plot using polygon function plot(polygon,type='n',xlab="Eastings (km)",ylab="Northings (km)",main="Polygon File") polygon(polygon) # plot as spatial polygon object plot(spatial.polygon,axes=TRUE) title(xlab="Eastings (km)",ylab="Northings (km)",main="Spatial Polygon") # Note that area 23 (argyll-bute) consists of 8 separate polygons nrepeats[23] plot(spatial.polygon[23],add=TRUE,col="red")
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