R-变量存储为形式类RasterLayer，缺少数据内容

Question

Defining a new raster layer (Sentinel 2 MSI)

> ras1 = raster ("T45QVG_20161209T045202_B02.jp2")
> summary (ras1)
1st Qu.                       1160
Median                        1230
3rd Qu.                       1300
Max.                          2221
NA's                             0
Warning message:
In .local(object, ...) :
  summary is an estimate based on a sample of 1e+05 cells (0.08% of all cells)

Now, assigning the defined raster layer to another variable

> ras2 = raster (ras1)
> summary (ras2)
layer
Min.       NA
1st Qu.    NA
Max.       NA
NA's       NA

Also,

> ras1
class       : RasterLayer 
dimensions  : 10980, 10980, 120560400  (nrow, ncol, ncell)
resolution  : 10, 10  (x, y)
extent      : 399960, 509760, 2590200, 2700000  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=utm +zone=45 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0
data source : /home/riyas/Data/Work files/Data samples/Sentinel 2-MSI/S2A_MSIL1C_20161209T045202_N0204_R076_T45QVG_20161209T045602.SAFE/GRANULE/L1C_T45QVG_A007652_20161209T045602/IMG_DATA/T45QVG_20161209T045202_B02.jp2 
names       : T45QVG_20161209T045202_B02 
values      : 0, 65535  (min, max)

Contains all the values, but

> ras2
class       : RasterLayer 
dimensions  : 10980, 10980, 120560400  (nrow, ncol, ncell)
resolution  : 10, 10  (x, y)
extent      : 399960, 509760, 2590200, 2700000  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=utm +zone=45 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0 

After assigning to a new variable everything messed-up!!

Answer 1

Calling raster on a RasterLayer object will only create an empty RasterLayer object, which has the same attributes as the original object (such as extent, resolution, size) but has no values.

Meaning, ras2 <- raster(ras1) will create ras2 , which is an empty raster with Sentinel-2 dimensions. That's also why calling summary is returning NA s.

If you want to assign it to a new variable, so making a simple copy, you can just run ras2 <- ras1 .