Requirements and feature parity

Where the requirements come from

The functional scope of version 1.0 is feature parity with the closed-source NMEASimulator 1.6.1 by panaaj, reconstructed from its public README, its release notes from 1.0.0 to 1.6.1 and the requests and bug reports in its issue tracker. Its users' unresolved requests become improvements in NMEA Simulator X. No code from that application is used.

Simulation modes

Requirement	Parity	Improvement over the reference
Delta mode: seed values plus periodic change; keyboard arrows for speed and heading	Yes	Every value individually overridable
Steering mode with rudder angle	Yes	Rate of turn derived from rudder, exposed as ROT
Follow GPX track, GPX route and KML track; concatenate segments	Yes	Interpolate along legs at a set speed when timestamps are missing; jump to a point
Use <time>, <course> and <speed> from track points when present	Yes
Record output to a log file and replay it with pause and step	Yes	Seek to a position; replay plain third-party NMEA logs as well
Autostart the stream on launch	Yes

Data and sentences

Requirement	Parity	Improvement over the reference
GNSS: RMC, GGA, GLL, GSA, GSV, VTG, ZDA; fix on/off; altitude	Yes	Configurable satellite count and HDOP
Heading and speed: HDG, HDM, HDT, VHW, VBW	Yes	ROT sentence
Depth and water: DPT, DBT, MTW	Yes
Wind: MWV apparent, MWD true	Yes
Autopilot: APB, RMB with a destination set on the map	Yes	XTE sentence; sentences kept within 82 characters
Rudder: RSA	Yes
AIS own vessel: VDO and VDM	Yes	Can be disabled independently
Propulsion: engine RPM and temperature	Yes
Configurable talker ID	Yes	Per sentence as well as global
Manually entered additional sentences	Yes	Checksum recalculated automatically
IEC 61162-450 TAG block prefix	Yes
Enable or disable individual sentences	Partial in reference	Full per-sentence control and per-sentence rate
Signal K delta output with hello message, context vessels or aircraft	Yes
ViewSync UDP for Google Earth and Liquid Galaxy	Yes

Transports

Requirement	Parity	Improvement over the reference
Serial port with detected and manually entered paths, custom baud rate	Yes
TCP server	Yes	TCP client
UDP unicast, broadcast with interface selection, multicast	Yes	Explicit broadcast address override
WebSocket server	Yes
Output interval down to 50 ms	Yes	Per-sentence rates
Several simultaneous outputs	No	Yes, each with its own filter

Platform and operations

Requirement	Parity	Improvement over the reference
Windows, macOS and Linux desktop builds	Yes (macOS lapsed in reference)	Built, checked and published by the release workflow for every release: Windows x64 installer and portable ZIP, macOS arm64 and x86_64 disk images, Linux x86_64 and aarch64 AppImages and a Flatpak
Installation without paid signing	Signed installers in reference	Ad-hoc signed macOS bundles, SHA-256 checksums, documented first-launch steps; manifests for winget, Scoop, a Homebrew tap and Flathub prepared for every release, submission pending
Settings survive restart	Unreliable in reference	Versioned profiles with migrations
Works without internet (map tiles)	Fragile in reference	Offline tile cache and graceful fallback
Command-line control	No	Headless CLI, shipped in every package; a remote control endpoint is not implemented
Open source	No	GPL-3.0

Out of scope for 1.0

• NMEA 2000 over CAN, including fast packets. The encoder layer is designed to host it later.
• AIS targets other than own vessel, and the TTM sentence.
• Scenario scripting.