0004 GPL-3.0 license

• Status: accepted
• Date: 2026-09-22

Context and problem statement

The project is published as free and open-source software. The reference application had no public source and no license. Which license should NMEA Simulator X use?

Decision drivers

• Keep the software and its derivatives free and open.
• Compatibility with Qt's open-source licensing (LGPL v3 / GPL v3).
• Compatibility with the other dependencies (GeographicLib: MIT, CLI11: BSD-3, Catch2: BSL-1.0).

Considered options

1. GPL-3.0.
2. Apache-2.0.
3. MIT.

Decision outcome

Option 1, GPL-3.0-only. It guarantees that improvements to the simulator remain available to the community, aligns naturally with Qt's open-source terms and is compatible with every dependency in use. Permissive licenses were considered but the project owner prefers the copyleft guarantee.

Consequences

• Every source file may carry an SPDX header SPDX-License-Identifier: GPL-3.0-only.
• Contributions are accepted under the same license, as stated in CONTRIBUTING.md.
• Qt is linked dynamically so that its LGPL obligations are met by shipping the Qt libraries alongside the application.