Assignment 2: GDAL

Assignment 2: GDAL#

In this assignment you will learn and practice how to use GDAL and OGR to process geodata in the command line and to write shell scripts to automatise and document your workflows.

For each of the following exercises a template script is provided in the ./fossgis_assignment_02/scripts folder. The scripts already contain a few short comments (lines starting with :: or #) which describe what the GDAL/OGR commands in the following lines are supposed to do. However, these commands are still missing. Your task will be to fill these in. Writing and executing shell scripts is different for Windows and Mac/Linux users. Therefore, in this assignment

Windows users should work with the files ending with .bat
Mac/Linux users work with the files ending with .sh

The data for this assignment is stored in ./fossgis_assignment_02/data. It contains the following files:

gadm36_SVN.gpkg: GADM Administrative areas of Slovenia
N45E014_sub.gpkg: Digital elevation model covering parts of Slovenia
n45_e013_1arc_v3_sub.tif: Digital elevation model covering parts of Slovenia

Submission:#

This assignment should be done and submitted in pairs of 2 students. You may choose with whom to work with until November 1st. Afterwards groups will be assigned randomly. Post your preferred groups in this issue.

Submission deadline: Friday, Nov 15 2024 on GitLab

Deliverables: The final folder/file structure of your repository should look like this.

|__ fossgis_assignment_02
	|__ data
	|___ documentation
		|__ 01_crs.md
		|__ 02_driver.md
		|__ 03_spatial_resolution.md
		|__ 04_bands_layers.md
		|__ 05_merge.md
		|__ 06_advantages.md
	|___ scripts  
		|__ 01_metadata.bat (windows)
		|__ 01_metadata.sh (linux/mac)
		|__ 02_merge_dem.bat (windows)
		|__ 02_merge_dem.sh (linux/mac)
		|__ 03_color_relief.bat (windows)
		|__ 03_color_relief.sh (linux/mac)
	|___ figures
		|__ color_relief_koper.jpg
		|__ color_relief_XXX.jpg (replace XXX with a district name)

If you have questions or problems create a new issue on Gitlab: https://courses.gistools.geog.uni-heidelberg.de/fossgis/fossgis_assignment_02/-/issues

0. Preparation#

Fork and clone the repository to your computer. Set your repo to “private” on GitLab when forking it or change the settings on GitLab later (Settings - General - Visibility). You can invite your group partner to your repo in the GitLab menu: Manage - Members.
Watch the tutorial videos on GDAL/OGR.

For a short introduction into GDAL watch this video (The “Installation” part is not relevant for you, since you’ve already installed GDAL with QGIS). It might also be worth looking at some of the videos in this playlist for more instructions on how to use GDAL/OGR.

To solve the following exercises refer to the GDAL documentation.

1. Explore metadata of the files#

Open your OSGeo shell (Windows) or command line (mac/linux). Move into the directory ./fossgis_assignment_02/scripts and execute the first script by calling ./01_metadata.bat (Windows) or ./01_metadata.sh (Unix/Mac). This should print Printing info about input files: on your command line.

Note: If you get an error, you might have to make the file executable by calling chmod +x ./scripts/commands_ex01.sh once.

Figure out the commands which prints out information about each of the datasets in the ./fossgis_assignment_02/data folder using the commands gdalinfo and ogrinfo. When they work add them to the script.

Note: If you execute the script and you get the error message No such file or directory you have to check whether the file paths in your script are correct. The script should be executed from the ./fossgis_assignment_02/scripts directory.

Based on the output of the commands answer the questions 1 to 4 located in the ./documentation.

Track your changes: Create a commit containing the changes to the script and the documentation and push it to GitLab.

2. Merge the DEM files#

Open your OSGeo shell (Windows) or command line (mac/linux). Move into the directory ./fossgis_assignment_02/scripts and execute the second script by calling ./02_merge.bat (Windows) or ./02_merge.sh (Unix/Mac). This should print Merging DEM files: on your command line.
Add a command to the script which merges the two dem files ./data/N45E014_sub.gpkg and ./data/n45_e013_1arc_v3_sub.tif using the command gdal_merge. The output file should contain only 1 band and should be stored in ./data/dem_merge.tif.
Add a command to the script which merges the two dem files ./data/N45E014_sub.gpkg and ./data/n45_e013_1arc_v3_sub.tif using the command gdalbuildvrt. The output file should contain only 1 band and should be stored in ./data/dem_buildvrt.vrt.
Based on the resulting files and the GDAL documentation answer questions 5 and 6 located in the ./documentation folder.

Track your changes: Create a commit containing the changes to the script and the documentation and push it to GitLab.

3. Create color relief image for different districts#

In final script create a color relief image for a selected district of Slovenia.

Fig. 1: Color relief of the disctict 'Koper' in Slovenia

Open your OSGeo shell (Windows) or command line (mac/linux). Move into the directory ./fossgis_assignment_02/scripts and execute the third script by calling ./03_color_relief.bat (Windows) or ./03_color_relief.sh (Unix/Mac). Add the missing commands to the script according to the following exercises.

1. Extract the target district#

Select the Slovenian district with the name Koper from the gadm36_SVN.gpkg file and save it to a new file called koper.shp using the ogr2ogr tool.

Hint: Take a close look at the examples given in the ogr2ogr documentation.

Track your changes: Create a commit containing the changes to the script and push it to GitLab.

2. Clip and reproject the DEM to the district#

Clip the dem file dem_merge.tif (from the previous exercise) to the selected district in koper.shp and reproject it to the coordinate reference system EPSG:32632. Save the result to a new file koper_dem.tif.

Track your changes: Create a commit containing the changes to the script and push it to GitLab.

3. Create a color relief image#

Create a color relief image based on the koper_dem.tif file using GDAL. Use the color_text.txt file as color_text_file parameter. The output file should be saved as ./fossgis_assignment_02/figures/color_relief_koper.jpg.

Track your changes: Create a commit containing the changes to the script and the new image and push it to GitLab.

4. Apply the script to a different district#

Replace all instances of the district name ‘Koper’ in your script with another district. Save the script and run it again. You should get a second image.