aspect: Aspect or orientation of the slope

Description

Calculates the aspect of every grid cell in a digital elevation model (DEM) from the output of cellgradient, which is a set of unit vectors normal to every grid cell in the DEM.

Usage

aspect(cgrad, degrees = FALSE)

Arguments

cgrad

A 3D array of dimensions [nrow(dem), ncol(dem), 3], where the third dimensions are the x, y, z component of the unit vectors normal to the surface of the DEM grid cells.

degrees

Logical. If FALSE, returns radians, if TRUE, returns degreees.

Value

Aspect or orientation of the slope.

Details

Uses atan2() to compute the orientation within the range \([0, 2\pi]\)

Examples

Run this code

# NOT RUN {
# Create a west-east facing ramp
slpwe = rep(1,10)  %o% c(1:5,4:1)
# calculate the aspect at every node or grid cell (it should be 270 or 90 degrees):
cgr = cgrad(slpwe,1)
aspect(cgr,degrees=TRUE)

# }
# NOT RUN {
 ## raster package display nicer than image and handles projections:
# Calculate the aspect of a rough mountain area in the pyrinees
zipfile = tempfile()
download.file("https://meteoexploration.com/R/insol/data/dempyrenees.asc.zip",zipfile)
header = read.table(unz(zipfile,'dempyrenees.asc'),nrows=6)
dem = read.table(unz(zipfile,'dempyrenees.asc'),skip=6)
dem = as.matrix(dem)
unlink(zipfile)
cellsize = header[5,2]
aspectdem = aspect(cgrad(dem,cellsize),degrees=TRUE)
image(t(aspectdem[nrow(aspectdem):1,]),col=grey(1:100/100))

require(raster)
demfile = tempfile()
download.file("https://meteoexploration.com/R/insol/data/dempyrenees.tif",demfile)
dem = raster(demfile)
aspectdem = aspect(cgrad(dem),degrees=TRUE)
aspectdem = raster(aspectdem,crs=projection(dem))
extent(aspectdem) = extent(dem)
plot(aspectdem,col=grey(1:100/100))
unlink(demfile)
# }