performs linear shifts of value ranges either to match min/max of another image (y)
or to any other min and max value (ymin and ymax).
Arguments
- x
SpatRaster or numeric vector. Image to normalise.
- y
SpatRaster or numeric vector. Reference image. Optional. Used to extract min and max values if ymin or ymax are missing.
- xmin
Numeric. Min value of x. Either a single value or one value per layer in x. If xmin is not provided it will be extracted from x.
- xmax
Numeric. Max value of x. Either a single value or one value per layer in x. If xmax is not provided it will be extracted from x.
- ymin
Numeric. Min value of y. Either a single value or one value per layer in x. If ymin is not provided it will be extracted from y.
- ymax
Numeric. Max value of y. Either a single value or one value per layer in x. If ymax is not provided it will be extracted from y.
- forceMinMax
Logical. Forces update of min and max data slots in x or y.
- ...
additional arguments passed to
terra::writeRaster()
Value
Returns a SpatRaster of the same dimensions as the input raster x but shifted and stretched to the new limits.
Details
Providing xmin and xmax values manually can be useful if the raster contains a variable of a known, fixed value range,
e.g. NDVI from -1 to 1 but the actual pixel values don't encompass this entire range.
By providing xmin = -1 and xmax = 1 the values can be rescaled to any other range,
e.g. 1 to 100 while comparability to other rescaled NDVI scenes is retained.
Examples
lsat2 <- lsat - 1000
lsat2
#> class : SpatRaster
#> dimensions : 310, 287, 7 (nrow, ncol, nlyr)
#> resolution : 30, 30 (x, y)
#> extent : 619395, 628005, -419505, -410205 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=utm +zone=22 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
#> source(s) : memory
#> names : B1_dn, B2_dn, B3_dn, B4_dn, B5_dn, B6_dn, ...
#> min values : -946, -982, -989, -996, -998, -869, ...
#> max values : -815, -913, -908, -873, -852, -854, ...
## Rescale lsat2 to match original lsat value range
lsat2_rescaled <- rescaleImage(lsat2, lsat)
lsat2_rescaled
#> class : SpatRaster
#> dimensions : 310, 287, 7 (nrow, ncol, nlyr)
#> resolution : 30, 30 (x, y)
#> extent : 619395, 628005, -419505, -410205 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=utm +zone=22 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
#> source(s) : memory
#> names : B1_dn, B2_dn, B3_dn, B4_dn, B5_dn, B6_dn, ...
#> min values : 54, 18, 11, 4, 2, 131, ...
#> max values : 185, 87, 92, 127, 148, 146, ...
## Rescale lsat to value range [0,1]
lsat2_unity <- rescaleImage(lsat2, ymin = 0, ymax = 1)
lsat2_unity
#> class : SpatRaster
#> dimensions : 310, 287, 7 (nrow, ncol, nlyr)
#> resolution : 30, 30 (x, y)
#> extent : 619395, 628005, -419505, -410205 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=utm +zone=22 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
#> source(s) : memory
#> names : B1_dn, B2_dn, B3_dn, B4_dn, B5_dn, B6_dn, ...
#> min values : 0, 0, 0, 0, 0, 0, ...
#> max values : 1, 1, 1, 1, 1, 1, ...