dem-handler

Utility package for handling various Digital Elevation Models (DEMs). The package enables access to data stored in cloud as well as local copies of dem datasets.

Functionality

The core functionality of this package is to provide mosaicked DEMs for arbitrary bounds. This is valuable for creating a mosaicked DEM that covers a scene. The package provides high level functions for supported DEMs, and low level functions that can be used to handle custom DEMs.

The DEM mosaicking functions have the following features:

• When requesting a DEM for bounds that include the ocean, the mosaicked DEM will include the ocean, setting the value of non-land pixels to 0 (height above the geoid).
• If a geoid height model is provided, the height above the ellipsoid can be returned.
• The functions work for DEM tiles stored in the cloud or locally.
• The mosaicked DEM can be returned in memory, as well as saved to a file for reuse.
• When a DEM has different resolutions, the mosaicked DEM will be returned with the highest resolution.
• If the DEM is requested over the antimeridian, the request will be split into Eastern and Western hemisphere components, then merged back together in an appropriate local coordinate reference system.

For more information on how the above functionality was implemented, see the design documentation.

Supported DEMS

• Copernicus Global 30m (cop_glo30)
• REMA (2m,10m, ...)

Usage

Create mosaicked DEM for bounds from cloud files

import os
from dem_handler.dem.cop_glo30 import get_cop30_dem_for_bounds
from dem_handler.dem.rema import get_rema_dem_for_bounds

import logging
logging.basicConfig(level=logging.INFO)

#Set the bounds and make a directory for the files to download

bounds = (72,-70, 73, -69)
save_dir = 'TMP'
os.makedirs(save_dir, exist_ok=True)

#The copernicus Global 30m DEM 

get_cop30_dem_for_bounds(
    bounds = bounds,
    save_path = f'{save_dir}/cop_glo30.tif',
    adjust_at_high_lat=False,
    cop30_folder_path = save_dir,
    ellipsoid_heights = False,
    download_dem_tiles = True
)

# The REMA DEM (32m)

get_rema_dem_for_bounds(
    bounds=bounds,
    save_path=f'{save_dir}/rema.tif',
    resolution=32,
    bounds_src_crs=4326,
)

Developer Setup

This repository uses pixi to manage the environment through the pyproject.toml file.

Note that installing a pixi environment will automatically install the dem-handler project in editable mode.

Using pixi is beneficial as it allows us to store named requirements in the pyproject.toml file, and provides a pixi.lock file that captures specific versions whenever the pixi environment is solved/installed.

Install pixi

Follow the pixi installation guide.

Install pixi environments

Environments are associated with the project.

• The default environment contains packages required for the code base (e.g. gdal, rasterio).
• The test environment contains everything from the default environment, PLUS packages required for tests (e.g. pytest).

cd to the repository folder and install the environments:

To install both environments, run

pixi install --all

Run predefined tasks

Pixi supports tasks (similar to using a Makefile) which can help automate common actions. In the repo, we have the following tasks, associated with the test environment:

• download_test_data, which will download test data from AWS
• test, which depends on download_test_data and will then run pytest

To run tests, use

pixi run test

Run a single command using pixi

For the default environment, use

pixi run <command>

For the test environment, use

pixi run -e test <command>

Activate the environment

For longer sessions, you can activate the environment by running

pixi shell

or

pixi shell -e test

To exit the shell, run

exit

Add dependencies

If wanting to install from conda-forge, use

pixi add <conda-forge-package>

If wanting to install from pypi, use

pixi add --pypi <pypi-package>

When a new package, consider whether it is required to run the code, or to do development/run tests.

If needed for tests, add it to the test environment:

pixi add --feature test --pypi <pypi-package>

Contact

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