[英]How to compute the area or number of pixels for selected region in R?
I am drawing a region over a raster files but I need to know how many pixels are covered in this box (by means the area): the raster file is 1440 pixels*720 lines``(25km*25km)
. 我正在栅格文件上绘制一个区域,但我需要知道此框中覆盖了多少像素(通过面积表示):栅格文件为
1440 pixels*720 lines``(25km*25km)
。
example: 例:
saf <- stack(system.file("external/rlogo.grd", package="raster"))
plotRGB( saf )
e <- drawExtent()
So after this I drew e
as a box but how many pixels/how much is the area? 因此,在此之后我将
e
绘制为一个框,但是面积为多少像素/多少? Thanks 谢谢
Try using raster::crop
... 尝试使用
raster::crop
...
crop(saf , e )
#class : RasterBrick
#dimensions : 40, 50, 2000, 3 (nrow, ncol, ncell, nlayers)
#resolution : 1, 1 (x, y)
#extent : 23, 73, 26, 66 (xmin, xmax, ymin, ymax)
#coord. ref. : +proj=merc
#data source : in memory
#names : red, green, blue
#min values : 0, 0, 0
#max values : 255, 255, 255
And if you just want the number of cells... 如果您只想要细胞数量...
ncell( crop(saf , e ) )
#[1] 2000
And to eliminate NA.... 并消除NA。
x <- crop( saf , e )
ncell( ! is.na(x[]) )
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