ChinyereRuth / TopographyR

It looks at topographical anlysis in R (One Line, Title Case)

Overview

This repository contains an R function for calculating the slope and aspect from a Digital Elevation Model (DEM) using the raster package. The function calculate_slope_aspect takes a raster object representing the DEM as input and returns two raters representing slope and aspect.

Function description

Function used

calculate_slope_aspect(dem)

Input

DEM for North Western Territories (NWT): A raster object representing the Digital Elevation Modelof North Western Territory for Canada in 2022.

Output

list (slope, aspect): A list containing two rasters:

• slope: A raster representing the calculated slope in degrees.
• aspect: A raster representing the calculated aspect in degrees.

Usage

Load the raster package:

#install.packages(“raster”)

library(raster)

## Loading required package: sp

Load the DEM of NWT

elevation_raster <- raster("/Users/chinyereottah/Desktop/Env/TopographyR/data-raw/NWTDEM_2022.tif")

Use the function which was derived

calculate_slope_aspect <- function(dem) {
  # Calculate slope
  dzdx <- focal(dem, matrix(c(-1,0,1,-2,0,2,-1,0,1), nrow=3, ncol=3),
                fun=function(x) {sum(x)})

  dzdy <- focal(dem, matrix(c(1,2,1,0,0,0,-1,-2,-1), nrow=3, ncol=3),
                fun=function(x) {sum(x)})

  slope <- atan(sqrt(dzdx^2 + dzdy^2))

  # Convert slope to degrees
  slope <- slope * (180 / pi)

  # Calculate aspect
  aspect <- atan2(dzdy, -dzdx)

  # Convert aspect to degrees
  aspect <- (aspect * (180 / pi) + 360) %% 360

  return(list(slope = slope, aspect = aspect))
}
## example of how you can use this function

# Load DEM
elevation_raster <- raster("/Users/chinyereottah/Desktop/Env/TopographyR/data-raw/NWTDEM_2022.tif")

Calculate slope and aspect

result <-calculate_slope_aspect(elevation_raster)

result <- calculate_slope_aspect(elevation_raster)

Access the result

slope_raster <- result$slope
aspect_raster <- result$aspect

Plot the result

plot(slope_raster, main="Slope")

plot(aspect_raster, main="Aspect")

Example usage

Load DEM

calculate_slope_aspect <- function(dem) {
  # Calculate slope
  dzdx <- focal(dem, matrix(c(-1,0,1,-2,0,2,-1,0,1), nrow=3, ncol=3),
                fun=function(x) {sum(x)})

  dzdy <- focal(dem, matrix(c(1,2,1,0,0,0,-1,-2,-1), nrow=3, ncol=3),
                fun=function(x) {sum(x)})

  slope <- atan(sqrt(dzdx^2 + dzdy^2))

  # Convert slope to degrees
  slope <- slope * (180 / pi)

  # Calculate aspect
  aspect <- atan2(dzdy, -dzdx)

  # Convert aspect to degrees
  aspect <- (aspect * (180 / pi) + 360) %% 360

  return(list(slope = slope, aspect = aspect))
}
## example of how you can use this function

# Load DEM
elevation_raster <- raster("/Users/chinyereottah/Desktop/Env/TopographyR/data-raw/NWTDEM_2022.tif")

Calculate slope and aspect

result <-calculate_slope_aspect(elevation_raster)

Access the slope and aspect rasters

slope_raster <- result$slope
aspect_raster <- result$aspect

Plot the results

plot(slope_raster, main="Slope")

plot(aspect_raster, main="Aspect")