r - 如何使用多边形切割砖 block ？

Question

我有一个生物气候变量的砖块文件，砖块是由四个 30 秒的砖块合并而成的，所以它有点大。我想通过使用多边形作为边界进行切割来获取我的研究区域的砖块文件。我该怎么办？否则，如果不能用砖来做，我可以用光栅来做吗？

先谢谢了~

马可

Answer 1

退房 extent()如果要将砖裁剪为较小的矩形。还有 drawExtent()如果您更愿意通过单击进行选择。

编辑:由于您使用了“cut”和“mask”这两个术语，我不确定我是否理解正确，但这里有两种方法可能会有所帮助。你甚至可以同时使用两者。

# an example with dimensions: 77, 101, 3  (nrow, ncol, nlayers)
myGrid_Brick <- brick(system.file("external/rlogo.grd", package="raster"))

# a simple polygon within those dimensions
myTriangle_P <- Polygon(cbind(c(10, 80, 50, 10), c(10, 20, 65, 10)))
myTriangle_Ps <- Polygons(list(myTriangle_P), "fubar")
myTriangle_SP <- SpatialPolygons(list(myTriangle_Ps))
myTriangle_Ras <- rasterize(myTriangle_SP, myBrick)

# this will crop a brick to minimal rectangle that circumscribes the polygon
# extent(myCrop) is smaller than extent(myGrid) but no values are changed
myCrop_Brick <- crop(myGrid_Brick, myTriangle_SP)

# while this converts every coordinate that is NA in
# the mask to become NA in the returned brick
# while leaving the brick extent unchanged
myMask_Brick <- mask(myGrid_Brick, myTriangle_Ras)