DEM-Shadows

Generate high-resolution terrain shadow rasters and animations from DEM GeoTIFFs.

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Table of Contents

• Overview
• Features
• Installation
• Project Structure
• Quick Start
  • 1. Generate Shadows
  • 2. Animate Shadows
  • 3. Cumulative Shadow Map
• CLI Reference
  • dem-shadows-generate
  • dem-shadows-animate
  • dem-shadows-cumulate
• Examples
• Notebooks
• Testing
• Streamlit App
• Author
• License

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Overview

dem-shadows is a lightweight Python toolchain for:

• Merging DEM tiles
• Converting DEMs to metric projected CRS
• Computing per-timestamp shadow rasters using the insolation package
• Auto-detecting latitude, longitude, and timezone from DEM extent
• Rendering animated GIFs of shadow progression
• Rendering cumulative “shadow exposure maps"

The goal is to provide easy, reproducible, and open-source shadow modelling for any DEM.

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Features

✔ Merge DEM tiles automatically
✔ Auto lat/lon from DEM center
✔ Auto timezone inference via tzfpy
✔ Robust shadow modeling (insolation sunvector + doshade)
✔ Zero-dependency GIF animation (Pillow only)
✔ Transparent or white-background output modes
✔ Cumulative exposure computation
✔ Optional Streamlit GUI
✔ Fully cross-platform (Windows / Linux / macOS)

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Installation

Clone & install locally

git clone https://github.com/marcop11/dem-shadows.git
cd dem-shadows
pip install -e .

Requirements

Automatically installed:

• rasterio
• numpy
• pandas
• Pillow
• tqdm
• astral
• insolation>=0.1.9
• tzfpy

Optional:

pip install streamlit

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Project Structure

dem-shadows/
│
├── app/
│   └── streamlit_app.py
│
├── examples/
│   └── dem.tif              # Example DEM for README & demos
│
├── img/
│   ├── app.png
│   ├── icon.svg
│   ├── logo.svg
│   ├── zh_example_sh.png
│   ├── zh_example_dtm.png
│   ├── zh_example_ortho.png
│   ├── zh_example_sh_cum.png
│   └── zh_example_animate.gif
│
├── notebooks/
│   └── try_it_yourself.ipynb
│
├── src/
│   └── dem_shadows/
│       ├── shadows.py       # DEM → shadows
│       ├── animate.py       # GIF generation
│       ├── analysis.py      # Cumulative shadows
│       ├── preprocess.py
│       ├── utils.py
│       ├── schedule.py
│       ├── config.py
│       └── __init__.py
│
├── tests/
│   └── test_basic.py
│
├── README.md
├── pyproject.toml
└── requirements.txt

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Quick Start

1. Generate Shadows

Generate a single shadow at 11:55 on March 8th 2025 — automatically detects lat/lon + timezone:

dem-shadows-generate ^
  --dem-dir "examples" ^
  --out-dir "out" ^
  --auto-latlon ^
  --auto-timezone ^
  --start 2025-03-08 ^
  --end 2025-03-08 ^
  --only-time 11:55

Minimal example for a whole day shadow generation hourly on March 8th 2025 — automatically detects lat/lon + timezone:

dem-shadows-generate ^
  --dem-dir "examples" ^
  --out-dir "shadows_day" ^
  --auto-latlon ^
  --auto-timezone ^
  --start 2025-03-08 ^
  --end 2025-03-08

Resulting output (example):

shadows_day/
│
├── shadow_20250308T070000_EuropeZurich.tif
├── shadow_20250308T080000_EuropeZurich.tif
├── shadow_20250308T090000_EuropeZurich.tif
├── ...
└── schedule.csv

Each GeoTIFF contains:

• 0 = shadow
• 1 = sunlit
• 255 = nodata

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2. Animate Shadows

Create a GIF from the folder:

dem-shadows-animate ^
  --shadow-folder "shadows_day" ^
  --out-gif "shadows_day.gif"

Example GIF (included in repo):

Shadows of Zürich on 8th March 2025.

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3. Cumulative Shadow Map

dem-shadows-cumulate ^
  --shadow-folder "shadows_day" ^
  --out "shadow_cumulative.tif"

This produces a raster where the value of each pixel equals:

Number of hours of sun per pixel

Example Cumulative Shadows (included in repo):

Cumulative shadows of Zürich on 8th March 2025.

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CLI Reference

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dem-shadows-generate

usage: dem-shadows-generate [OPTIONS]

Required

--dem PATH                # or --dem-dir PATH (automerge)
--out-dir PATH
--start YYYY-MM-DD
--end   YYYY-MM-DD

Optional

--auto-latlon
--auto-timezone
--lat FLOAT
--lon FLOAT
--timezone "Europe/Zurich"
--step-minutes 60
--only-time HH:MM
--dem-pattern "*.tif"

---

dem-shadows-animate

usage: dem-shadows-animate [OPTIONS]

Required

--shadow-folder PATH
--out-gif PATH

Optional

--start YYYY-MM-DD
--end YYYY-MM-DD
--hour INT
--minute INT
--duration-ms 250
--sample-stride 1
--target-width 900
--target-height 0
--scale-factor FLOAT
--no-timestamp
--font-path PATH

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dem-shadows-cumulate

usage: dem-shadows-cumulate [OPTIONS]

--shadow-folder PATH
--out PATH

Python API example

You can also call the core functionality from Python:

from pathlib import Path
from datetime import date
from dem_shadows import LocationConfig, ShadowConfig, run_shadow_batch

dem_path = Path("examples/dem.tif")
out_dir = Path("out")

loc = LocationConfig(latitude=47.38, longitude=8.53, timezone="Europe/Zurich")
cfg = ShadowConfig(
    dem_path=dem_path,
    out_dir=out_dir,
    location=loc,
    start_date=date(2025, 3, 8),
    end_date=date(2025, 3, 8),
    step_minutes=60,
)

run_shadow_batch(cfg)

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Examples

Example DEM

Located at:

examples/
├── dem.tif
├── dem_is.tif
└── dem_fr.tif

Example imagery and shadow screenshots

Located at:

img/
├── app.png
├── icon.svg
├── logo.svg
├── zh_example_sh.png
├── zh_example_dtm.png
├── zh_example_ortho.png
├── zh_example_sh_cum.png
└── zh_example_animate.gif

These are referenced inside this README.

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Notebooks

Google Colab notebook:

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Testing

Run all tests:

pytest -q

The tests/ folder contains:

tests/
└── test_basic.py

test_basic.py ensures basic imports and config structures work.

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Streamlit App

Try the live web interface:

You can run the GUI with:

streamlit run app/streamlit_app.py

Features:

• Upload DEM
• Choose start/end time
• Generate shadows
• Preview results
• Download outputs and GIF

Find more digital elevation or terrain models to try:

• Switzerland
• Iceland
• France

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Author

Marco Pizzolato – marcop11

Date: 24.11.2025

Version: 0.1.0

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License

This project is licensed under GPLv3.