Page Comparison

In R raster calculations, involving one or more raster layers, can be conducted in 3 different ways:

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

#==================================================================================
# Re-scale raster cell values
#==================================================================================
# The rasters cell values are in scale 0-255, so we re-scale them a 0-100 scale to represent the Green Cover Fraction in %.
# Generalized version: ((X - Xmin) * 100) / (Xmax - Xmin)
SPGC.StudyArea.2010q3.rl = SPGC.StudyArea.2010q3.rl * 100 / 255
SPGC.StudyArea.2010q3.rl

Div

style	background-color: white; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

## class       : RasterLayer 
## dimensions  : 295, 206, 60770  (nrow, ncol, ncell)
## resolution  : 30, 30  (x, y)
## extent      : 1484025, 1490205, -1996985, -1988135  (xmin, xmax, ymin, ymax)
## coord. ref. : +proj=aea +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=132 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs 
## data source : in memory
## names       : SPGC_2010q3 
## values      : 39.21569, 77.2549  (min, max)

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

SPGC.StudyArea.2011q3.rl = SPGC.StudyArea.2011q3.rl * 100 / 255
SPGC.StudyArea.2011q3.rl

Div

style	background-color: white; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

## class       : RasterLayer 
## dimensions  : 295, 206, 60770  (nrow, ncol, ncell)
## resolution  : 30, 30  (x, y)
## extent      : 1484025, 1490205, -1996985, -1988135  (xmin, xmax, ymin, ymax)
## coord. ref. : +proj=aea +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=132 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs 
## data source : in memory
## names       : SPGC_2011q3 
## values      : 39.21569, 76.86275  (min, max)

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

#----------------------------------------------------------------------------------
# Raw Change (in %)
#----------------------------------------------------------------------------------
# We use Raster Algegra to calculate Raw Change (i.e. change in %) in SPGC

SPGC.StudyArea.Diffq3.rl = SPGC.StudyArea.2011q3.rl - SPGC.StudyArea.2010q3.rl
SPGC.StudyArea.Diffq3.rl

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

# Method 1: Compute using Raster Algebra
# --------------------------------------
SPGC.StudyArea.StdDiffq3.rl = ((SPGC.StudyArea.2011q3.rl - cellStats(SPGC.StudyArea.2011q3.rl,mean)) / cellStats(SPGC.StudyArea.2011q3.rl,sd)) - 
                               ((SPGC.StudyArea.2010q3.rl - cellStats(SPGC.StudyArea.2010q3.rl,mean)) / cellStats(SPGC.StudyArea.2010q3.rl,sd))
SPGC.StudyArea.StdDiffq3.rl

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

# Method 2: Compute using Higher Level Functions from the Package `raster`
# ------------------------------------------------------------------------

calc.DiffStdRaster.f = function(rla, r1b)
{
    diff.std.rl = ((r1b - cellStats(r1b, mean)) / cellStats(r1b, sd)) - ((rla - cellStats(rla, mean)) / cellStats(rla, sd))
    return(diff.std.rl)
} # calc.DiffStdRaster.f = function(rla, r1b)
SPGC.StudyArea.StdDiffq3.rl.m2 = calc.DiffStdRaster.f(SPGC.StudyArea.2010q3.rl, SPGC.StudyArea.2011q3.rl)
SPGC.StudyArea.StdDiffq3.rl.m2

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

# Method 3: Compute using function `normImage` in package 'RStoolbox'
# -------------------------------------------------------------------
SPGC.StudyArea.StdDiffq3.rl.m3 = normImage(SPGC.StudyArea.2011q3.rl) - normImage(SPGC.StudyArea.2010q3.rl)
SPGC.StudyArea.StdDiffq3.rl.m3

...

Div

style	background-color: #F8F9F9; border: 1px solid #666; font-size: 12px; padding: 0.5rem 0.5rem;

# Remove unnecessary (i.e. repeated) objects
#ls(pattern="SPGC.StudyArea.StdDiffq3")
rm(SPGC.StudyArea.StdDiffq3.rl.m2, SPGC.StudyArea.StdDiffq3.rl.m3)
#ls(pattern="SPGC.StudyArea.StdDiffq3")

Versions Compared

Old Version 10

New Version 11

Key