如果光栅值NA搜索并提取最近的非NA像素

Question

在将光栅的值提取到点时,我发现我有几个NA,而不是使用函数的参数buffer和fun参数extract,而是我想将最近的非NA像素提取到重叠的点NA.

我正在使用基本提取功能:

data.extr<-extract(loc.thr, data[,11:10])

Answer 1

这是一个不使用缓冲区的解决方案.但是,它会分别为数据集中的每个点计算距离图,因此如果数据集很大,它可能无效.

set.seed(2)

# create a 10x10 raster
r <- raster(ncol=10,nrow=10, xmn=0, xmx=10, ymn=0,ymx=10)
r[] <- 1:10
r[sample(1:ncell(r), size = 25)] <- NA

# plot the raster
plot(r, axes=F, box=F)
segments(x0 = 0, y0 = 0:10, x1 = 10, y1 = 0:10, lty=2)
segments(y0 = 0, x0 = 0:10, y1 = 10, x1 = 0:10, lty=2)

# create sample points and add them to the plot
xy = data.frame(x=runif(10,1,10), y=runif(10,1,10))
points(xy, pch=3)
text(x = xy$x, y = xy$y, labels = as.character(1:nrow(xy)), pos=4, cex=0.7, xpd=NA)

# use normal extract function to show that NAs are extracted for some points
extracted = extract(x = r, y = xy)

# then take the raster value with lowest distance to point AND non-NA value in the raster
sampled = apply(X = xy, MARGIN = 1, FUN = function(xy) r@data@values[which.min(replace(distanceFromPoints(r, xy), is.na(r), NA))])

# show output of both procedures
print(data.frame(xy, extracted, sampled))

#          x        y extracted sampled
#1  5.398959 6.644767         6       6
#2  2.343222 8.599861        NA       3
#3  4.213563 3.563835         5       5
#4  9.663796 7.005031        10      10
#5  2.191348 2.354228        NA       2
#6  1.093731 9.835551         2       2
#7  2.481780 3.673097         3       3
#8  8.291729 2.035757         9       9
#9  8.819749 2.468808         9       9
#10 5.628536 9.496376         6       6