如何计算多边形质心和边缘之间的最大距离 [英] How to compute greatest distance between polygon centroid and edge

问题描述

我有一个SpatialPolygons(DataFrame)对象，例如SpP

I have a SpatialPolygons(DataFrame) object, e.g. SpP

library(sp)    
Sr1 = Polygon(cbind(c(2,4,4,1,2),c(2,3,5,4,2)))
Sr2 = Polygon(cbind(c(5,4,2,5),c(2,3,2,2)))
Sr3 = Polygon(cbind(c(4,4,5,10,4),c(5,3,2,5,5)))
Sr4 = Polygon(cbind(c(5,6,6,5,5),c(4,4,3,3,4)), hole = TRUE)
Srs1 = Polygons(list(Sr1), "s1")
Srs2 = Polygons(list(Sr2), "s2")
Srs3 = Polygons(list(Sr3, Sr4), "s3/4")
SpP = SpatialPolygons(list(Srs1,Srs2,Srs3), 1:3)

我想为每个多边形计算其质心(coordinates(SpP))到同一多边形内任何其他点的最大距离(我假设这个最远的点将在边缘上?).

I would like to, for each polygon, calculate the greatest distance between its centroid (coordinates(SpP)) to any other point within the same polygon (I assume this furtherest away point will be on the edge?).

有人可以告诉我该怎么做吗?

Can someone show me how to do that?

推荐答案

这是我创建的一个简单函数，该函数针对给定的多边形计算质心，并使用基本几何来查找点距质心最远，返回其质心坐标:

Here is a simple function I created that for a given polygon calculates the centroid, and the uses basic geometry to find with point is furthest from the centroid, returning its coordinates:

library(sp)
library(rgeos)
library(ggplot2)

Sr2 = Polygon(cbind(c(5,4,2,5),c(2,3,2,2)))
Srs2=Polygons(list(Sr2), "s2")
spPol=SpatialPolygons(list(Srs2))

find_furthest_point=function(polygon){
  coords=fortify(polygon)[,c(1:2)]  
  center=as.data.frame(gCentroid(polygon))
  longs=coords[,1]
  lats=coords[,2]

  dist_fx=function(long, lat, center=center){
    dist=sqrt((long-center[1])^2+(lat-center[2])^2)
    return(dist)
  }
  dists=mapply(dist_fx, longs, lats, MoreArgs=list(center))
  furthest_index=as.integer(which(dists==max(dists)))
  furthest=coords[furthest_index,]  
  return(furthest)
}

find_furthest_point(Sr2)

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