ITM Longley-Rice: Irregular Terrain Model for Rust

A high-performance, scientifically-validated Rust implementation of the ITS Irregular Terrain Model (ITM), also known as the Longley-Rice model.

Overview

itm-longley-rice provides a modern, memory-safe port of the standard atmospheric propagation model used for frequencies between 20 MHz and 20 GHz. This implementation is based directly on the original NTIA C++ source code (v1.3), ensuring functional parity with the established scientific reference while providing the safety and performance benefits of the Rust ecosystem.

This library is designed for integration into large-scale simulations, including Unreal Engine 5 and other C++ environments, via a robust C-API.

Scientific Backing

The core algorithm predicts terrestrial radiowave propagation based on electromagnetic theory and extensive empirical data collected by Anita Longley and Phil Rice.

Supported Propagation Mechanisms

• Free Space Loss: Standard LOS propagation.
• Diffraction: Multi-faceted implementation using Vogler's smooth-earth approximation and Bullington knife-edge methods.
• Troposcatter: Selection and calculation of tropospheric scatter for trans-horizon paths.
• Variability Analysis: Statistical modeling of signal reliability across time, location, and situation.

Technical References

This implementation precisely follows the algorithms defined in the following primary references:

• NTIA Technical Report TR-82-100: A Guide to the Use of the ITS Irregular Terrain Model in the Area Prediction Mode.
• NTIA Technical Report ERL 79-ITS 67: Prediction of Tropospheric Radio Transmission Loss Over Irregular Terrain: A Computer Method.
• Hufford, G. A. (1985): Memorandum on the ITS Irregular Terrain Model, version 1.2.2.

Key Core Features

• Point-to-Point (P2P) Mode: Calculate path loss using actual terrain elevation profiles sampled from GIS data or game engine geometry.
• Area Prediction Mode: Generate statistical coverage estimates based on terrain roughness (delta_h) when specific profiles are unavailable.
• Parallelized Signal Radius Calculation: Efficiently determine the maximum distance a signal can travel before dropping below a specified sensitivity threshold. This is implemented as a multi-point parallel search using Rayon for high performance.
• C-API Integration: Built-in support for static linking into Unreal Engine, allowing real-time electromagnetic warfare (EW) and signal simulation.

Heritage

This project is a pragmatic, high-fidelity port of the NTIA/ITS C++ implementation. It maintains the internal numeric heuristics and mathematical structures found in the canonical FORTRAN and C++ versions, ensuring that results match validated government benchmarks.

Getting Started

Refer to the following documentation for integration details:

• C-API Usage Guide: Detailed instructions for Unreal Engine and C/C++ integration.

FFI feature note: The C-API is enabled by default. Rust-only consumers can disable it with --no-default-features or by setting default-features = false in their dependency entry.

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For technical inquiries regarding the underlying ITM model, refer to the official NTIA/ITS documentation.

Continuous Integration

This project uses GitHub Actions for continuous integration and validation:

• CI Workflow: Tests on Windows, Linux, and macOS with stable and beta Rust toolchains
• NTIA Validation: Automated testing against NTIA reference implementation outputs
• Security Audit: Daily dependency vulnerability scanning with cargo-audit and cargo-deny
• Code Coverage: Automated coverage reports via Codecov
• Release Automation: Automatic cross-platform builds and crates.io publishing on version tags

All tests must pass before merging, ensuring scientific accuracy and code quality.

Contributing

Contributions are welcome! Please read CONTRIBUTING.md for guidelines.

Before submitting a PR:

1. Run cargo test --all to ensure all tests pass
2. Run cargo test --test ntia_validation to validate against NTIA reference
3. Run cargo fmt and cargo clippy to maintain code quality
4. Add tests for new functionality

License

This project is licensed under the MIT License - see the LICENSE file for details.

Original ITM License

The original ITS Irregular Terrain Model developed by NTIA is in the public domain as a work of the U.S. Federal Government (Title 15 USC § 105). This Rust implementation is a derivative work that maintains compatibility with the original while adding modern safety guarantees and performance optimizations.

Attribution

When using this library, please acknowledge:

• Original ITM: National Telecommunications and Information Administration (NTIA)
• Original Authors: Anita Longley and Phil Rice
• This Implementation: Daniel Santana

References

• Original NTIA ITM Repository: https://github.com/NTIA/itm
• NTIA ITM License: https://github.com/NTIA/itm/blob/master/LICENSE.md