@sailingnaturali/signalk-depth-offsets

Derive environment.depth.belowKeel and environment.depth.belowSurface from environment.depth.belowTransducer using your vessel's measured transducer offsets — for depth sounders that only emit NMEA0183 DBT (depth below transducer) with no offset field.

Zero runtime dependencies.

What it does

A DBT-only sounder maps to environment.depth.belowTransducer in Signal K, but the keel/surface-referenced depths you actually navigate by (under-keel clearance) are never produced. This plugin derives them, using the canonical Signal K convention:

belowKeel    = belowTransducer + transducerToKeel    (transducerToKeel < 0)
belowSurface = belowTransducer + surfaceToTransducer  (surfaceToTransducer > 0)

The offsets come from the data model itself — environment.depth.transducerToKeel and environment.depth.surfaceToTransducer (typically set from baseDeltas.json). This plugin carries no offsets of its own; it's the single transform, the profile is the single source of truth. A derived path is only emitted when its offset is present.

Install

Signal K admin → Appstore → search "depth offsets", or npm install @sailingnaturali/signalk-depth-offsets in your Signal K data dir. Set environment.depth.transducerToKeel / surfaceToTransducer in your vessel's baseDeltas.json (or any source). No plugin configuration.

License

MIT