DEM Differencing Toolkit

Version: 1.0.0

What is this repo?

This repository provides generalized scripts that enable accurate and interpretable differencing of digital elevation models (DEMs) with:

• Differing grids and pixel sizes
• Different horizontal and vertical coordinate reference systems
• Varying extents

Future It includes options for local and supercomputer systems, plus working examples with data to help users gain confidence with the workflow.

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How does it work?

This repository contains (or will contain) three major components:

1. Basic DEM Differencing Script

A standalone script for differencing two DEMs on a local machine.

2. Supercomputer-Adapted Script

A version optimized for HPC systems (like UAF's Chinook) with accompanying .sh batch files.

3. Example Implementation

Working examples using provided data to demonstrate both scripts.

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Why create this?

The goal is to establish a standard pipeline for DEM differencing.

I developed this toolkit because I needed to difference ~40 DEMs of one region with vastly different:

• Coordinate reference systems
• Spatial extents
• Resolutions

While xDEM provides valuable standardization, my workflow required additional functionality not covered by their established pipelines.

For GEOS 694: I've successfully adapted this code into a class format (Task #1). Next steps include adapting for Chinook (Task #2) and implementing effective parallelization (Secondary Task #1).

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Repository Contents

File	Description
dem_diff.py	Main script for differencing DEMs with different grids, CRS, and formats. Requires users to specify horizontal/vertical CRS and NoData values.
requirements.txt	Python package dependencies for running the scripts.
demDiff.yml	Conda environment file for creating a local environment.

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Installation

# Clone the repository
git clone https://github.com/miajac/diffDEM.git
cd diffDEM

# Create conda environment
conda env create -f demDiff.yml
conda activate demDiff

# Or install dependencies manually
pip install -r requirements.txt

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Usage

Command Line

Edit the parameters at the bottom of dem_diff.py in the if __name__ == "__main__": block:

differencer = DEMDifferencer(
    path_dem1="path/to/dem1.tif",
    nickname_dem1="DEM1",
    src_vcrs_dem1="NAVD88",  # or "Ellipsoid", "EGM96", etc. 
    src_hcrs_dem1="EPSG:3338",
    nodata_dem1=-9999,
    path_dem2="path/to/dem2.tif",
    nickname_dem2="DEM2",
    src_vcrs_dem2="Ellipsoid",
    src_hcrs_dem2="EPSG:32606",
    nodata_dem2=-9999,
    path_dest="path/to/output/directory",
    coregister=True,  # Optional: set True for Nuth & Kääb coregistration
    roi=None  # Optional: provide vector for region of interest
)

Then run:

python dem_diff.py

The differenced DEM will be saved to: path_dest/nickname_dem2_nickname_dem1.tif

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As a Python Module (Optional)

You can also import and use the class in your own scripts:

from dem_diff import DEMDifferencer

differencer = DEMDifferencer(
    path_dem1="path/to/dem1.tif",
    # ... (same parameters as above)
)
differencer.run()

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Acknowledgments

This toolkit builds heavily on xDEM, an open-source Python package for analyzing digital elevation models.

xDEM citation:

xDEM contributors. (2024). xDEM (v0.1.0). Zenodo. https://doi.org/10.5281/zenodo.11492983