循环以提取特定的光栅/空间点对

Question

我有许多不重叠的点形状文件，我想把它们归因于analagous光栅，也不重叠。我想用光栅数据来确定这些点的属性。对于我正在使用的一些光栅数据类型，我能够先合并光栅，然后合并属性。但是，我的最后几组光栅数据没有相同的原点，因此我无法合并/拼接它们。我试图在不合并光栅的情况下，将点归因于光栅。这需要我在特定的空间点-光栅对上使用extract（）。我用一个唯一的4个字母的名称为每个空间点文件命名，这也是我希望extract（）使用的光栅名称的一部分。

我在下面创建了一个可复制的示例，它模拟了我的数据和问题。有谁能建议我如何为extract（）编写循环代码，以将要提取的空间点文件提取到具有解析名称的光栅？

或者，如果更好地/可能地组合所有空间点，只需循环提取所有光栅，然后管理数据，使所有提取的值都位于数据帧的一个向量或列中，那可能会更好。

我使用的是RStudio 1.2.1335

注意：我将此问题发布到GIS Stack Exchange，但没有收到任何答案，希望交叉发布可以。

library(raster)
library(sp)   

#create point shapefiles
loc1 <- data.frame(x = c(-100,-90, -80, -70),
                  y = c(-100,-90, -80, -70))
loc2 <- data.frame(x = c(-100,-90, -80, -70),
                   y = c(100,90, 80, 70))
loc3 <- data.frame(x = c(100,90, 80, 70),
                   y = c(100,90, 80, 70))
coordinates(loc1) <- ~x+y
sp.loc1<- SpatialPoints(loc1,proj4string = CRS("+proj=longlat +datum=WGS84 +no_defs"))
coordinates(loc2) <- ~x+y
sp.loc2<- SpatialPoints(loc2,proj4string = CRS("+proj=longlat +datum=WGS84 +no_defs"))
coordinates(loc3) <- ~x+y
sp.loc3<- SpatialPoints(loc3,proj4string = CRS("+proj=longlat +datum=WGS84 +no_defs"))
plot(sp.loc1)

#create rasters which have a common part of the naming convention of point shapefiles targeting for attribution
loc1_blablabla<- raster(xmn=-200, xmx=0, ymn=-200, ymx=0)
loc1_blablabla
ncell(loc1_blablabla)
#it has 64800 cells
values(loc1_blablabla)<-1:64800
plot(loc1_blablabla, add=TRUE)
plot(sp.loc1, add=TRUE)
loc2_blablabla<- raster(xmn=-200, xmx=0, ymn=0, ymx=200)
values(loc2_blablabla)<-1:64800
loc3_blablabla<- raster(xmn=0, xmx=200, ymn=0, ymx=200)
values(loc3_blablabla)<-1:64800

#plot all, but first create extent poly
#borrowed some code from here:https://gis.stackexchange.com/questions/206929/r-create-a-boundingbox-convert-to-polygon-class-and-plot/206952
library(rgeos)
ext.box<-rgeos::bbox2SP(n=250, s=-250, w=-250, e=250)
plot(ext.box)
plot(loc1_blablabla, add=TRUE)
plot(loc2_blablabla, add=TRUE)
plot(loc3_blablabla, add=TRUE)
plot(sp.loc1, add=TRUE)
plot(sp.loc2, add=TRUE)
plot(sp.loc3, add=TRUE)

#now attempt to extract raster values at points for multiple non-overlapping point and raster files ie. extract(loc1_blablabla, loc1)
#try lapply as in: https://stackoverflow.com/questions/59164538/create-a-loop-to-extract-data-from-multiple-raster
#create list as below, however, with my real data I would use list.files()
loc.list<-list(loc1,loc2,loc3)
rast.list<-list(loc1_blablabla,loc2_blablabla,loc3_blablabla)
attr.data<-lapply(rastlist.extract,loc.list)
#this doesn't work -- i think I need coordinates as the last term, not a list of spatial points

#also tried a for loop, but this gave error:  "Error in (function (classes, fdef, mtable): unable to find an inherited method for function ‘shapefile’ for signature ‘"list"’"
for (i in 1:length(loc.list)) {
  #this reads in each spatialpoint file and assigns each sp's name to the variable 'sp.name'
  sp.name<-shapefile(loc.list[i]) 
  attr.data<-data.frame(coordinates(sp.name),
                             extract(rast.list[grep(sp.name,rast.list)],sp.name))
  #eventually add this line to affix the new vector attr.data to the coordinates for each plot:  names(attr.data)<-c("x","y","raster.value")
}

Answer 1

你不能按文件名匹配它们吗？如果是这样，那就是你应该做的。你们提出的建议有多种可能，但你们似乎在试图解决你们自己创造的问题——而避免所有这些可能会容易得多。

我会用

library(raster)
r <- lapply(raster_file_names, raster)
s <- lapply(shapefile_names, shapefile)

然后绕着这些

用你的示例数据

library(raster)
p1 <- SpatialPoints(cbind(x = c(-100,-90, -80, -70), y = c(-100,-90, -80, -70)))
p2 <- SpatialPoints(cbind(x = c(-100,-90, -80, -70), y = c(100,90, 80, 70)))
p3 <- SpatialPoints(cbind(x = c(100,90, 80, 70), y = c(100,90, 80, 70)))
pts <- list(p1, p2, p3)

r1 <- raster(xmn=-200, xmx=0, ymn=-200, ymx=0, vals=1:64800)
r2 <- raster(xmn=-200, xmx=0, ymn=0, ymx=200, vals=1:64800)
r3 <- raster(xmn=0, xmx=200, ymn=0, ymx=200, vals=1:64800)
ras <- list(r1, r2, r3)

e <- list()
for (i in 1:length(ras)) {
    e[[i]] <- extract(ras[[i]], pts[[i]])
}
e
#[[1]]
#[1] 32581 29359 26137 22915
#[[2]]
#[1] 32581 35839 39097 42355
#[[3]]
#[1] 32581 35803 39025 42247