形状文件的质心

Question

我通过使用unionSpatialPolygons融合多边形创建了一个shapefile，如何找到已创建的新多边形的坐标？

Answer 1

以下是两个选项，具体取决于您要计算的质心类型。我从一些维基百科页面中获取了这些算法。

# polyx and polyy are the x and y coordinates of the polygon vertices 
# notice had to negate these calcs in final line...
 require(pracma,quietly=TRUE)

pchit <- polyarea(polyx,polyy)
    centx <- centy <- 0
    for (kk in 1:(length(polyx)-1) ) {
        centx <- centx + (polyx[kk]+polyx[kk+1]) * (polyx[kk]*polyy[kk+1]-polyx[kk+1]*polyy[kk])
        centy <- centy + (polyy[kk]+polyy[kk+1]) * (polyx[kk]*polyy[kk+1]-polyx[kk+1]*polyy[kk])
    }
    centx <- -1/pchit/6 * centx
    centy <- -1/pchit/6 * centy
    #  These next two are for vertex centroid, rather than polygon centroid
    # centx <- mean(polyx)
    # centy <- mean(polyy)