如何从其最大值位于多边形内的栅格中提取xy坐标? [英] How to extract xy-coordinates from raster where its highest value is located within a polygon?

问题描述

给定的是栅格以及SpatialPolygonsDataframe.为了检索多边形区域内栅格的最大值，可以使用raster :: extract.它工作正常.

如何在多边形区域内另外获取提取的栅格最高值的坐标?

 #创建栅格r<-栅格(ncol = 36，nrow = 18)r []<-runif(ncell(r))#从GridTopology创建SpatialPolygonsgrd<-GridTopology(c(-150，-50)，c(40，40)，c(8，3))Spol<-as(grd，"SpatialPolygons")#创建SpatialPolygonsDataFrame重心<-坐标(Spol)x<-重心[，1]y<-重心[，2]SPDF<-SpatialPolygonsDataFrame(Spol，data = data.frame(x = x，y = y，row.names = row.names(Spol))))#为每个SpatialPolygon提取栅格的最大值ext<-raster :: extract(r，SPDF，fun = max) 

*示例代码取自R文档

解决方案

您可以在 extract 中使用 cellnumbers = TRUE 参数，然后使用 sapply 获取单元格编号:

  ext<-raster :: extract(r，SPDF，cellnumbers = TRUE)v<-t(sapply(ext，function(i)i [which.max(i [，2])，]))#储存格值#[1，] 185 0.9303460#[2，] 188 0.9821190#[3，] 154 0.9926290#[4，] 232 0.8907819#[5，] 234 0.9998510 

获取坐标:

  xyFromCell(r，v [，1])#x y#[1，] -135 35#[2，] -105 35#[3，] -85 45#[4，] -25 25#[5，] -5 25 

given is a raster as well as a SpatialPolygonsDataframe. In order to retrieve the highest value of the raster within the area of a polygon, raster::extract can be used. It works fine.

How to get additionally the coordinates of the extracted highest value of the raster within the area of a polygon?

# create raster
r <- raster(ncol=36, nrow=18)
r[] <- runif(ncell(r))
# create SpatialPolygons from GridTopology
grd <- GridTopology(c(-150, -50), c(40, 40), c(8, 3))
Spol <- as(grd, "SpatialPolygons")
# create SpatialPolygonsDataFrame
centroids <- coordinates(Spol)
x <- centroids[,1]
y <- centroids[,2]
SPDF <- SpatialPolygonsDataFrame(Spol, data=data.frame(x=x, y=y, row.names=row.names(Spol)))
# extract max value of raster for each SpatialPolygon
ext <- raster::extract(r, SPDF, fun=max)

*example code is taken from R-documentation

解决方案

You can use the cellnumbers=TRUE argument in extract, followed by a sapply to get the cell number:

ext <- raster::extract(r, SPDF, cellnumbers=TRUE)
v <- t(sapply(ext, function(i) i[which.max(i[,2]), ] ))

#      cell     value
# [1,]  185 0.9303460
# [2,]  188 0.9821190
# [3,]  154 0.9926290
# [4,]  232 0.8907819
# [5,]  234 0.9998510

To get the coordinates:

xyFromCell(r, v[,1])

#         x   y
# [1,] -135  35
# [2,] -105  35
# [3,]  -85  45
# [4,]  -25  25
# [5,]   -5  25

这篇关于如何从其最大值位于多边形内的栅格中提取xy坐标?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！