从栅格单元内的光栅中提取随机点

您没有指定采样的所有条件,所以我在这里进行一些假设。 可以对每个栅格多边形采样一个点并提取值。以下是您如何一蹴而就并抱着最好的希望:

# pick random points per each grid  cell and plot
set.seed(357)
pickpts <- sapply(gridpolygon@polygons, spsample, n = 1, type = "random")
sapply(pickpts, plot, add = TRUE)

# extract values of raster cells at specified points
sapply(pickpts, FUN = extract, x = r)

或者可以在循环中进行,并进行采样,直到得到非NA值。

N <- length(gridpolygon@polygons)
result <- rep(NA, times = N)

for (i in 1:N) {
  message(sprintf("Trying polygon %d", i))

  pl <- gridpolygon@polygons[[i]]
  candval <- result[i] # start with NA

  # sample until you get a non-NA hit
  while (is.na(candval)) {
    pickpoint <- spsample(pl, n = 1, type = "random")
    candval <- extract(x = r, y = pickpoint)
  }

  result[i] <- candval

}
result

 [1] 0.4235214 0.6081435 0.9126583 0.1710365 0.7788590 0.9413206 0.8589753
 [8] 0.0376722 0.9662231 0.1421353 0.0804440 0.1969363 0.1519467 0.1398272
[15] 0.4783207