Learn to Georeference a raster map in QGIS. Follow the steps given below:
- Open QGIS
- To start with, Georeference GDAL Plugin is required for georeferencing. To install the plugin Go to menu Plugins->Manage Plugins. It opens Manage Plugins diaologue box. Check the Georeference GDAL plugin check box in the dialogue box and click OK. The plugin will be listed as Georeferencer in the Raster menu.
- Go to Raster menu and select Georeferncer and click on Georeferencer. It opens Georeferencer dialogue box:
- In the dialogue box, select Open raster from the File menu and select the topographic map that you have. The selected map opens in the Georeferencer dialogue box. It also opens up a Coordinate Reference Selector dialogue box, which asks you to choose CRS for the input raster.
- Fill in the required parameters as shown below and click OK.
- You can change band combinations of the raster layer by selecting Raster properties from the Settings menu. Go to the top left corner of the map using zoom and pan buttons and select Add point from Edit menu.
- Click on the top left corner point of the map. It opens Enter map coordinates dialogue box. Enter the X and Y coordinates in the box as shown in image below and click OK. The entered point is now listed in the GCP table within the Georeferencer dialogue box. You can move the point and also delete the points if you have wrongly entered the coordinates.
- Similarly, add points for all the remaining three corners and their coordinates. Once all the four points have been entered they will be listed in the GCP table as shown in below image.
- Select Transformation settings from Settings menu and fill the boxes values as given in the image below and click OK.
- Now select Start georeferencing from the File menu. It starts georeferencing based on the points and parameters you have given and shows the progress monitor. After completing the process the georeferenced map khambat_topo2.tif opens in the main window. You save the GCP points used in the georeferencing for future use by selecting Save GCP points as from the File menu. It saves the GCP points with *.points extension.