Georeferencing1 in QGIS

Georeferencing Liberia’s Land Cover Map .PNG Image

Procedure:

1. Georeferencing in QGIS is done via the the “Georeferencer GDAL” plugin. This is a core plugin - meaning it is already part of your QGIS installation. You just need to enable it. Go to Plugins ‣ Manage and Install Plugins.

require(RCurl)

## Loading required package: RCurl

## Loading required package: bitops

library(knitr)
library(png)
library(grid)
img <- readPNG("/Users/calvingaye/Desktop/png/Picture1.png")
grid.raster(img)

2. Enable the Georeferencer GDAL plugin in the Installed tab.

library(png)
library(grid)
img1 <- readPNG("/Users/calvingaye/Desktop/png/Picture2.png")
grid.raster(img1)

3. The plugin is installed in the Raster menu. Click on Raster ‣ Georeferencer ‣ Georeferencer to open the plugin.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture3.png")
grid.raster(img)

4. The Georeferencer plugin window is divided into 2 sections. The top section where the raster will be displayed and the bottom section where a table showing your GCPs will appear.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture4.png")
grid.raster(img)

5. Now we will open our PNG image. Go to File ‣ Open Raster. Browse to the downloaded image of the scanned map and click Open.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture5.png")
grid.raster(img)

6. In the next screen, you will have asked to choose the raster’s coordinate reference system (CRS). This is to specify the projection and datum of your control points. If you have collected the ground control points using a GPS device, you would use the WGS84 CRS.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture6.png")
grid.raster(img)

7. You will see the image will be loaded on the top section.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture7.png")
grid.raster(img)

8. Load any shape file for Liberia in your QGIS work space: Click Layer ‣ Add layer ‣ Add vector layer.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture8.png")
grid.raster(img)

9. The image is loaded on the top screen.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture9.png")
grid.raster(img)

10. Create a point shape file with at least five points considering Liberia as your reference image. Click Layer ‣ Create Layer ‣ New Shapefile Layer.

img <- readPNG("/Users/calvingaye/Desktop/png/Picture10.png")
grid.raster(img)