4. Getting acquainted with Grass GIS

We will Grass GIS to process the data we have acquired. It will also let you understand the working of Grass GIS. Just follow the steps in this chapter and I will explain things as we go. We will use windows version of Grass GIS 7.8.

4.1. Starting Grass GIS

Create a folder inside your working directory and name it appropriately. We will use this folder for Grass. Open Grass GIS user interface by entering Grass GIS in the windows search box.

1. The user interface is shown below. The icon corresponding to ‘Add existing or create new database’ is circled red. Click this icon. The folder browser will be displayed where you need to select the folder.

Fig. 4.1 Grass User Interface

2. A dialog box as shown will be displayed. Click yes.

Fig. 4.2 Location Dialog

3. Name and description of project. Write the desired name and description in the next dialog box.

Fig. 4.3 Dialog Box for Name and Description

4.2. Create new location

In the next screen select the option to read CRS from a georeferenced data file. Click Next button.

Fig. 4.4 Create Folder for Grass Workspace

4.2.1. Select georeferenced file

In the next screen, select the elevation data file dem_rect.tif by clicking Browse button.

Fig. 4.5 Select the file

The next screen will show the projection of the data and summary. Our data has UTM Zone 45 projection. All the consequent file import will automatically be reprojected to this projection. Click Finish to complete the creation of grass location and import of elevation data. When you are asked to import the elevation data, click Yes. You will return to the starting screen. Click Start Grass GUI. The screen will be closed and two different user interfaces will be displayed.

4.2.2. User interfaces of Grass

Following image shows the user interface. In the previous versions, two separage user interfaces were used. First one to display layers and menus while the second one displayed map and related navigation tools. In the latest version, the interface is integrated as shown below. Unlike other softwares, GIS data cannot be displayed without importing to Grass format. There are five different tabs which can be used for various purposes which will explained as needed.

Fig. 4.6 Grass Working Interface

We have already imported elevation data to Grass. Let us try to display it. As shown in the figure, follow the steps below.

1. Click tool Add raster map layer.

2. In the next screen, click the drop down to show the available maps.

3. Select dem_rect which we have added earlier.

4. Now you can see the elevation raster added to the map display.

Alternatively, just go to Data tab at the bottom, refresh it and then double click the data named dem_rect.

Fig. 4.7 Add Existing Raster Layer to the Map Display