plot Ellipse限制点的百分比

Question

我使用ellipsoidhull()函数来导出一个椭圆,该椭圆界定x,y坐标中的所有点.然后我使用point.in.polygon()函数来预测一组新的X,Y坐标是否落在椭圆内部/外部.

而不是绘制一个限定(x,y)中所有点的椭圆,是否可以使用80%的点？可以选择80%的点以形成最紧凑或最小的椭圆区域.

> xy

x       y 
3.076   5.208
3.046   5.123
2.993   5.108
3.062   5.134
3.168   5.223
3.138   5.284
3.166   5.319
3.226   5.411
3.262   5.417
3.215   5.234
3.086   5.019
3.199   5.167
3.274   5.596
3.293   5.608
3.195   5.396
3.294   5.374
2.974   5.539
3.268   5.377
3.192   5.298
3.08    4.916
3.117   4.985
3.128   5.118
3.21    5.373
3.184   5.282
3.27    5.291
3.074   5.175

> Query
X       Y
3.03    5.008
2.99    5.018
2.987   4.944
2.994   4.899
2.911   4.963
2.913   4.942
2.966   4.969
3.079   5.011
3.096   5.268
2.992   5.169
3.205   5.466
3.257   5.776
3.154   5.563
3.16    5.192
3.12    5.446
3.271   5.719
3.154   5.478
3.143   5.454
3.123   5.439
3.075   5.224
3.264   5.56
3.288   5.404
3.237   5.499
3.207   5.47
3.207   5.459
3.11    5.23
3.301   5.605
3.139   4.823


library(cluster)
exy <- ellipsoidhull(as.matrix(xy))
ellipse <- predict(exy)
library("sp")
point.in.polygon(Query$X, Query$Y, ellipse.FAM[,1], ellipse.FAM[,2])

Answer 1

大概你正在使用cluster::ellipsoidhull.在另一个包中,该car::dataEllipse函数计算中心,形状和半径值并传递给ellipse.对于"假定的正常"情况,您可能会假设,相关代码是:

library(car)
dataEllipse
function(x,y, ....
...
else {
        shape <- var(cbind(x, y))
        center <- c(mean(x), mean(y))
    }
    for (level in levels) {
        radius <- sqrt(dfn * qf(level, dfn, dfd)

然后'ellipse'计算它传递给线的各个点.进行最终计算的代码是

ellipse <-
function (center, shape, radius, ....)
....
 angles <- (0:segments) * 2 * pi/segments
    unit.circle <- cbind(cos(angles), sin(angles))
    ellipse <- t(center + radius * t(unit.circle %*% chol(shape)))
    colnames(ellipse) <- c("x", "y")

因此,这两个函数的组合适用于您的数据:

getEparams <-function(x,y, level) { dfn <- 2
        dfd <- length(x) - 1
        shape <- var(cbind(x, y))
        center <- c(mean(x), mean(y))
        radius <- sqrt(dfn * qf(level, dfn, dfd))
        return(list(center=center, shape=shape, radius=radius) ) }

ellcalc <- function (center, shape, radius, segments=51){segments=segments
    angles <- (0:segments) * 2 * pi/segments
    unit.circle <- cbind(cos(angles), sin(angles))
    ellipse <- t(center + radius * t(unit.circle %*% chol(shape)))
    colnames(ellipse) <- c("x", "y")
    return(ellipse)}

evals <- getEparams(Query$X, Query$Y, 0.80)
plot(ellcalc(evals[["center"]], evals[["shape"]], evals[["radius"]]))
title(main='Output of plot(ellcalc(evals[["center"]], evals[["shape"]], 
                           evals[["radius"]]))\nStackOverflow Demonstration')
 points(Query$X, Query$Y, cex=0.3, col="red")

显然,您可以将ellcalc调用结果保存或传递给您想要的任何对象