L15: Rasters and Raster Operations 1

Reading Rasters, Attributes, Raster Subsetting, Vectorizing, Cropping

Bogdan G. Popescu
bogdan.popescu@johncabot.edu

John Cabot University

Today

Today’s agenda includes:

  • becoming familiar with others types of data in R:
  • raster layers
  • examining spatial and non-spatial properties of vectors

We will use sf, stars, and units packages.

Reminder: Spatial Data Classes in R

  • Spatial entries in GIS can be represented as a vector or as a raster

  • In the previous lecture, we examine vectors and geometric operations with vectors.

Raster

Rasters are matrices or an array representing a rectangular area on the surface of the earth.

They contain elements such as :

  • Origin (\(x_{max}\), \(y_{min}\)) and resolution (\(\delta_{x}\), \(\delta_{y}\))
  • Coordinate Reference System
  • Values
  • Dimensions (rows, column, layers)
  • Extent: \(x_{min}\), \(y_{min}\), \(x_{max}\), \(y_{max}\)

Raster

Raster with the Same Extent but Different Resolutions

Raster file formats

  • “Simple” rasters
    • GeoTIFF (.tif)
    • Erdas Imagine Image (.img)
  • “Complex” rasters (>3D and / or metadata)
    • HDF (.hdf, .he5)
    • NetCDF (.nc)

Using R packages for rasters

There is one important package that we will work with: stars

terra is also another important package developed by the same authors

Both contain classes, and extensive functions for working with rasters in R

We will mostly work with stars

The stars package

Unlike terra and raster, stars is very well integrated with sf

sf is the package that we have used for vector analysis.

Example of Raster: Luminosity

A typical example of raster is satellite luminosity

Within economics, researchers use satellite luminosity as a proxy for economic activity

Luminosity in 2013

Working with Luminosity

You can download satellite luminosity by going to https://www.ncei.noaa.gov/products/dmsp-operational-linescan-system


Working with Luminosity

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