SILVO — a Simplified Light–Vegetation Overlay model

SILVO is a lightweight 3D ray-tracing model for vegetation canopy structure, light interception, gap fraction, and illumination. It is designed for heterogeneous canopies such as orchards, open woodlands, agroforestry systems, and isolated trees using minimal inputs: tree crown position/size plus sun/view geometry.

Keywords: vegetation canopy model, light interception model, gap fraction, tree crown geometry, orchard simulation, agroforestry model, ray tracing.

It is designed to be fast and reproducible, and it is parallelised with OpenMP.

Table of contents

• What SILVO produces
• Quick start (Linux)
• Usage
• Help
• Inputs
• Outputs
• How to cite

What SILVO produces

• Gap fraction and sunlit/shaded fractions (soil & vegetation)
• Vertical structural proxies (density / profiles) that can constrain 1D RTMs (e.g., SAIL/SCOPE-type workflows)
• A quick-look render (PPM) and analysis-ready rasters (ENVI BIP + HDR)

Quick start (Linux)

1) Install build tools (Debian-based OS)

sudo apt update
sudo apt install -y build-essential

2) Clone the repository

git clone https://github.com/ahornero/silvo.git
cd silvo

3) Build

From the repository root:

make

The executable is created at (already precompiled in the repo for amd64)

./bin/silvo

4) Run an example

cd examples/ourique_default
./run_silvo.sh

Outputs are written in the folder where you run SILVO (e.g., inside the example directory) and from the previous example should generate a BIL (ENVI) file (with its header, hdr companion file) containing all the output as layers and a PNG image as preview.

Usage

By default, SILVO reads the following files from the current working directory:

• scene.txt
• settings.txt

But they can be chosen from the command line as arguments:

./bin/silvo --scene path/to/scene.txt --config path/to/settings.txt

Same applies for the solar and camera settings. Command-line values take precedence over settings.txt:

./bin/silvo --scene scene.txt --config settings.txt \
  --sza 35 --saa 120 --cza 0 --caa 0 --cds 600 --fov 30

Help

./bin/silvo -h
Usage: ./bin/silvo
        [-s|--scene scene_file (scene.txt)]
        [-c|--config config_file (settings.txt)]
        [--sza value] [--saa value] [--cza value] [--caa value] [--cds value] [--fov value]
        [-h] (show this)

Inputs

scene.txt (vegetation crowns)

Plain text. Each non-comment (#...) line contains:

x  y  z  radius

• Lines starting with # are ignored.
• z is typically 0 for flat terrain (SILVO places spheres sitting on the ground). Example:

# x   y   z   radius
0.0  0.0  0.0  2.5
8.0  0.0  0.0  2.0
0.0  8.0  0.0  3.0

settings.txt (camera + sun + flags)

Plain text key/value pairs, e.g.:

solar_zenith = 35
solar_azimuth = 120

camera_zenith = 0
camera_azimuth = 0
camera_distance = 600
camera_fov = 30

debug = 0
gap_fraction_profile_enabled = 0

Outputs

SILVO writes outputs to the current working directory:

• output_image.ppm — RGB quick-look render
• output.bip + output.hdr — ENVI BIP (15 bands, float32) + header
• Console metrics (stdout): gap fraction, sunlit/shaded fractions, normalised density
• Optional CSV profiles:
  • vertical_profile.csv (generated when camera_zenith == 90)
  • gap_fraction_profile.csv (generated when gap_fraction_profile_enabled = 1 and camera_zenith != 90)

How to cite

If you use SILVO in academic work, please cite:

Hornero, A., Prikaziuk, E., Hernandez-Clemente, R., van der Tol, C. (2026).
SILVO, a lightweight 3D illumination model to characterise the spatial structure of heterogeneous vegetation canopies.
International Journal of Applied Earth Observation and Geoinformation, 147, 105178. https://doi.org/10.1016/j.jag.2026.105178

@article{Hornero2026SILVO,
  title   = {SILVO, a lightweight 3D illumination model to characterise the spatial structure of heterogeneous vegetation canopies},
  author  = {Hornero, A. and Prikaziuk, E. and Hernandez-Clemente, R. and van der Tol, C.},
  journal = {International Journal of Applied Earth Observation and Geoinformation},
  volume  = {147},
  pages   = {105178},
  year    = {2026},
  issn    = {1569-8432},
  doi     = {10.1016/j.jag.2026.105178},
  url     = {https://doi.org/10.1016/j.jag.2026.105178}
}