Install QGIS 3.4 With GRASS Support On Ubuntu 18.04

by Sebastian Müller 52 views

Hey everyone! Having trouble getting GRASS to play nice with QGIS 3.4 on your Ubuntu 18.04 system? You're not alone! Many users face this hiccup where QGIS installs just fine, but GRASS tools throw an error saying, "This algorithm cannot be run :-( GRASS 7 can't be found on this system from a shell. Please install it or configure your ..." Don't worry; we've got you covered. This guide will walk you through a foolproof method to get QGIS 3.4 and GRASS working together seamlessly on your Ubuntu 18.04 machine.

Understanding the Issue

Before we dive into the solution, let's quickly understand why this problem occurs. QGIS relies on GRASS GIS for many geoprocessing tasks, especially those involving raster and vector data analysis. GRASS GIS isn't always installed alongside QGIS, or the system might not correctly recognize its location. The error message indicates that QGIS can't find the GRASS 7 installation, meaning the environment variables or paths aren't correctly set. This often happens even if you've installed GRASS because the system-wide configuration needs a little nudge. So, let's get those gears turning and make sure QGIS and GRASS can communicate effectively.

Prerequisites

Before we start, ensure you have a working installation of Ubuntu 18.04. You'll also need sudo privileges to install software and modify system settings. It's always a good practice to update your system's package list before installing new software. Open your terminal and run the following commands:

sudo apt update
sudo apt upgrade

These commands will update the package lists and upgrade any outdated packages on your system. This step ensures that you're working with the latest versions of software and dependencies, which can prevent potential conflicts during the installation process. Now that we've got the preliminaries out of the way, let's move on to the actual installation steps.

Step-by-Step Installation Guide

Step 1: Adding the QGIS Repository

The first step is to add the official QGIS repository to your system. This ensures that you're installing QGIS and its dependencies from a reliable source. The QGIS repository contains the latest versions of the software, including the one we need, QGIS 3.4. Open your terminal and add the QGIS repository key using the following command:

sudo apt-key add URI

Replace URI with the appropriate key URL for your QGIS version. For QGIS 3.4, you might need to add the specific repository key. A reliable method is to visit the QGIS download page and find the exact command for adding the key for your Ubuntu version. This key ensures that the packages you download are authenticated and haven't been tampered with. Think of it as a digital signature that verifies the software's integrity.

Next, add the QGIS repository to your system's software sources. This tells your system where to look for QGIS packages. Use the following command, replacing <QGIS VERSION> with the specific version you need (e.g., ubuntugis/ppa for the latest stable release):

sudo add-apt-repository deb https://qgis.org/debian <QGIS VERSION>

After adding the repository, update your package list to include the newly added repository. This step is crucial because it refreshes the list of available packages and ensures your system knows about the QGIS packages. Use the following command:

sudo apt update

Step 2: Installing QGIS and GRASS

Now that you've added the QGIS repository and updated your package list, you can install QGIS and GRASS together. This is the critical step where we ensure both QGIS and GRASS are installed in a way that they can communicate with each other. Use the following command:

sudo apt install qgis qgis-plugin-grass

This command installs QGIS and the GRASS plugin for QGIS. The qgis-plugin-grass package is essential because it provides the necessary integration between QGIS and GRASS. It includes the GRASS algorithms and tools that you can access directly from the QGIS interface. During the installation, you might be prompted to confirm the installation of additional dependencies. Type Y and press Enter to proceed. This command essentially sets the stage for QGIS and GRASS to work in harmony.

Step 3: Configuring GRASS Environment

Sometimes, even after installing QGIS and the GRASS plugin, you might still encounter the "GRASS 7 can't be found" error. This usually happens because the GRASS environment variables aren't correctly set. To fix this, you need to configure the GRASS environment so that QGIS can locate the GRASS installation. The easiest way to do this is to set the GRASS_PREFIX environment variable. This variable tells QGIS where to find the GRASS installation directory.

Open your terminal and edit the QGIS startup script. The location of this script may vary depending on your installation, but it's often found in /usr/bin/qgis. Use a text editor like nano or vim to open the script with administrative privileges:

sudo nano /usr/bin/qgis

Inside the script, add the following line before the line that starts QGIS (usually exec /usr/lib/qgis/qgis or similar):

export GRASS_PREFIX=/usr/lib/grass78

Replace /usr/lib/grass78 with the actual path to your GRASS installation. You can find this path by running whereis grass78 in the terminal. The output will show the location of the GRASS binaries, and you should use the parent directory as the GRASS_PREFIX. This command points QGIS in the right direction, ensuring it can find the GRASS installation.

Save the changes and exit the text editor. If you're using nano, press Ctrl+X, then Y, and then Enter. Now, let's move on to testing the setup.

Step 4: Testing the Installation

After configuring the GRASS environment, it's time to test whether QGIS can successfully access GRASS. Launch QGIS from your application menu or by typing qgis in the terminal. Once QGIS is open, go to Processing -> Toolbox. In the Processing Toolbox, you should see a section labeled GRASS 7. If you see this section, it means QGIS has successfully detected the GRASS installation. Congratulations, you're halfway there!

To further test the installation, try running a GRASS algorithm. For example, you can load a vector layer and try running the v.buffer algorithm to create a buffer around the features. If the algorithm runs without any errors, it confirms that GRASS is working correctly within QGIS. This final check ensures everything is functioning as expected.

Step 5: Troubleshooting Common Issues

Even after following these steps, you might encounter some issues. Here are a few common problems and their solutions:

  1. "GRASS 7 can't be found" error persists: Double-check the GRASS_PREFIX environment variable in the QGIS startup script. Make sure the path is correct and points to the GRASS installation directory. Also, ensure that you've saved the changes to the script correctly. Sometimes, a simple typo can cause this issue. This is like double-checking your map to ensure you're on the right path.

  2. GRASS algorithms are not listed in the Processing Toolbox: Ensure that the GRASS plugin is enabled in QGIS. Go to Plugins -> Manage and Install Plugins and check if the GRASS plugin is enabled. If it's not, enable it and restart QGIS. This is akin to turning on the engine of your GRASS toolbox.

  3. Errors during GRASS algorithm execution: This could be due to various reasons, such as incorrect input data or missing dependencies. Check the error message carefully and try to identify the cause. Sometimes, installing additional GRASS modules can resolve the issue. This is like fine-tuning your tools to get the best results.

Conclusion

Installing QGIS 3.4 with GRASS support on Ubuntu 18.04 can be a bit tricky, but with the right steps, it's definitely achievable. By following this comprehensive guide, you should be able to get QGIS and GRASS working together smoothly. Remember to add the QGIS repository, install the necessary packages, configure the GRASS environment, and test your installation. And don't forget to troubleshoot any common issues that might arise. With QGIS and GRASS at your fingertips, you'll be able to perform a wide range of geospatial analyses and create stunning maps. So, go ahead and explore the power of QGIS and GRASS!

If you have any questions or run into any problems, feel free to leave a comment below. Happy mapping, guys!