0

我有一个terra::rast图层n。我想只使用包提取某些层的值terra（我更喜欢这个包的答案而不是raster）。看来我不明白如何layer在函数中使用参数terra::extract。这是一个最小（几乎）工作示例：

rs1 = terra::rast(nrows = 3, ncols = 4)
terra::values(rs1) = 4:15
rs2 = terra::rast(nrows = 3, ncols = 4)
terra::values(rs2) = 25:36
rs3 = terra::rast(nrows = 3, ncols = 4)
terra::values(rs3) = 97:108
rs4 = terra::rast(nrows = 3, ncols = 4)
terra::values(rs4) = 51:62

rs = c(rs1, rs2, rs3, rs4)
names(rs) = paste0("layer", 1:nlyr(rs))

coords = matrix(data = c(0, 5, 10, -54, 0, 12), byrow = FALSE, ncol = 2)
colnames(coords) = c("x", "y")

terra::extract(x = rs, y = coords)[, c("layer1", "layer4")] # Works but not elegant in terms of memory
terra::extract(x = rs, y = coords, layer = c("layer1", "layer4")) # Does not work
terra::extract(x = rs, y = coords, layer = c(1, 4)) # Does not work

此代码提供以下错误：

Error in .local(x, y, ...) : length(layer) == nrow(y) is not TRUE

我不明白为什么层数应该等于y. 我想它应该是最大的层数x。如何专门提取第 1 层和第 4 层的给定坐标处的值（或任何其他层，这只是一个示例）？

4

1 回答 1

2

我猜你只是在寻找subset(). terra请在下面找到reprex。

代表

library(terra)

extract(x = subset(rs, c(1,4)), y = coords)
#>   layer1 layer4
#> 1     14     61
#> 2     10     57
#> 3     10     57

由reprex 包于 2021-11-02 创建(v0.3.0)

于 2021-11-02T16:26:30.850 回答