10 - Custom Region DEM

After working through fetchez, transformez, and globato, this final Day 2 exercise brings the workflow together by building a DEM for a custom coastal region. You will choose a small coastal area, apply the same globato build pattern used for the Fiji example, and review the resulting output for basic quality-control issues.

Export the Custom Recipe¶

Choose a small coastal region and apply the same workflow pattern used for the Fiji DEM.

General command:

globato cudem build -R WEST/EAST/SOUTH/NORTH -E 3s -O custom_test -P epsg:4326+3855 -M ms_binary_cudem:algos=interp_gmt -X 0:5 global-bathy-topo --export

Replace:

WEST/EAST/SOUTH/NORTH

with the selected coastal bounding box.

Example centered on the Nukuʻalofa, Tonga region:

globato cudem build -R -175.40/-175.00/-21.35/-21.00 -E 3s -O custom_test -P epsg:4326+3855 -M ms_binary_cudem:algos=interp_gmt -X 0:5 global-bathy-topo --export

The --export option writes the generated YAML workflow to a recipe file instead of running the full DEM build.

Expected recipe output:

custom_test_recipe.yaml

Open the exported recipe in a text editor and compare it with the Fiji recipe from Day 1.

Run the Custom Recipe¶

Run the exported recipe to generate the DEM:

globato cudem run custom_test_recipe.yaml

Expected final DEM:

custom_test_final.tif

Inspect the Output¶

Inspect the custom DEM the same way you inspected the Fiji output in the globato module:

gdalinfo custom_test_final.tif

Create a color shaded-relief image:¶

globato perspecto hillshade --help

Example hillshade command:

globato perspecto hillshade INPUT_DEM.tif OUTPUT_HILLSHADE.tif --cmap etopo --exag 3 

Basic Output Review¶

Review the generated DEM and hillshade using the following questions:

• Does the DEM cover the expected region?

• Are land and water in the correct locations?

• Are land elevations generally positive?

• Are underwater elevations generally negative?

• Are there missing-data areas or obvious gaps in source coverage?

• Are there edge or coastline artifacts?

• Are there interpolation artifacts or unexpected surface patterns?

• Does the hillshade show reasonable terrain and bathymetric structure?

• Do neighboring source datasets appear consistent?

• Are there areas that should be checked against local or independent data?

This is not a complete validation procedure. The goal is basic output review and quality-control thinking about the relationship between source data, workflow settings, and DEM quality, using tools available within the workshop environment.

Modify One Thing¶

After the first custom run, modify one part of the command or recipe.

Change the Region¶

Export a new recipe using a different bounding box:

globato cudem build -R WEST/EAST/SOUTH/NORTH -E 3s -O custom_region_v2 -P epsg:4326+3855 -M ms_binary_cudem:algos=interp_gmt -X 0:5 global-bathy-topo --export

Then run it:

globato cudem run custom_region_v2_recipe.yaml

Change the Resolution¶

Export a 1-arc-second version:

globato cudem build -R 178.25/178.65/-18.30/-17.95 -E 1s -O fiji_test_1s -P epsg:4326+3855 -M ms_binary_cudem:algos=interp_gmt -X 0:5 global-bathy-topo --export

Run the exported recipe:

globato cudem run fiji_test_1s_recipe.yaml

Alternatively, override the saved Fiji recipe:

globato cudem run fiji_test_recipe.yaml -E 1s -O fiji_test_1s

Compare the outputs:

gdalinfo fiji_test_final.tif
gdalinfo fiji_test_1s_final.tif

The goal is not to produce a perfect DEM. The goal is to understand how changes to the region, resolution, sources, and workflow settings affect the resulting output.

Wrap-Up and Next Steps¶

By the end of Day 2, participants should have:

• Reactivated the cudem environment

• Reviewed the Fiji test DEM

• Seen how fetchez, transformez, globato, and IVERT support the CUDEM workflow

• Explored source modules and YAML formatting

• Reviewed the role of vertical harmonization

• Generated or inspected a custom DEM recipe

• Reviewed DEM outputs for basic quality-control issues

• Understood how the Fiji recipe can be adapted to other coastal regions

Suggested Next Steps¶

• Explore additional source modules and module bundles

• Inspect additional example recipes

• Try a new coastal region

• Compare different output resolutions

• Add local or project-specific source data

• Begin adapting the workflow to your own project area

• Use IVERT or other independent data to assess the resulting DEM

• Continue using Zulip for questions, support, and sharing workflow ideas

Continuous DEMs Zulip