R\"terra\" 库中的 resample() 函数在特定情况下无法正常工作

Question

在下面的代码中，我尝试使用 resample(x, y, method = "sum") 将高分辨率栅格重新采样为低分辨率栅格。但是，重采样栅格在某些边缘显示 NA。

library(terra)
set.seed(42)

low_res <- rast(xmin = -1.05, xmax = 1.05, ymin = -0.05, ymax = 2.05, res = 0.5)

high_res <- rast(xmin = -1, xmax = 1, ymin = 0, ymax = 2, res = 0.01)
high_res[] <- runif(ncell(high_res))
plot(high_res, colNA = "darkblue")

resampled <- resample(high_res, low_res, method = "sum")
plot(resampled, colNA = "darkblue")
plot(as.polygons(low_res), add=TRUE, border='black', lwd=1) 

高分辨率栅格：

重采样栅格（深蓝色像元为 NA）：

但是，如果将低分辨率栅格的范围四舍五入（即删除 _.05），一切看起来都不错：

library(terra)
set.seed(42)

##################################
# only changed extent here
low_res <- rast(xmin = -1, xmax = 1, ymin = -0, ymax = 2, res = 0.5) 
##################################

high_res <- rast(xmin = -1, xmax = 1, ymin = 0, ymax = 2, res = 0.01)
high_res[] <- runif(ncell(high_res))
plot(high_res, colNA = "darkblue")

resampled <- resample(high_res, low_res, method = "sum")
plot(resampled, colNA = "darkblue")
plot(as.polygons(low_res), add=TRUE, border='black', lwd=1) 

重采样栅格：

Answer 1

好的，我认为，如果低分辨率栅格中的单元格不在高分辨率栅格的范围内，它将获得 NA 值（我希望不是这样).因此，作为一种解决方案，我尝试使用 extend() 在 high_res 栅格周围添加像元（我认为，扩展 high_res 的保守大小将是 low_res 栅格的分辨率大小）。下面的代码运行良好：

library(terra)

set.seed(42)
low_res <- rast(xmin = -1.05, xmax = 1.05, ymin = -0.05, ymax = 2.05, res = 0.5)

high_res <- rast(xmin = -1, xmax = 1, ymin = 0, ymax = 2, res = 0.01)
high_res[] <- runif(ncell(high_res))
plot(high_res, colNA = "darkblue")

#######################################
# add paddings around high_res raster
# with at least the resolution size of low_res raster
add_n_cells <- ceiling(res(low_res) / res(high_res))
high_res <- extend(high_res, add_n_cells)
plot(high_res, colNA = "darkblue")
#######################################

resampled <- resample(high_res, low_res, method = "sum")
plot(resampled, colNA = "darkblue")
plot(as.polygons(low_res), add=TRUE, border='black', lwd=1) 

高分辨率栅格扩展：

最终重采样栅格：