Create DPT-surface.js

Using surfaceToTransducer to calculate depth

sentences/DPT-surface.js

@@ -0,0 +1,26 @@
+/**
+Depth:
+$IIDPT,x.x,x.x,,*hh
+ I I_Sensor offset, >0 = surface transducer distance, >0 = keel transducer distance.
+ I_From Surface To Transduder
+
+ */
+// NMEA0183 Encoder DPT   $IIDPT,69.21,-0.001*60
+const nmea = require('../nmea.js')
+module.exports = function (app) {
+  return {
+    sentence: 'DPT',
+    title: 'DPT - Depth at Surface (using surfaceToTransducer)',
+    keys: [
+      'environment.depth.belowTransducer',
+      'environment.depth.surfaceToTransducer'
+    ],
+    f: function dpt (belowTransducer, surfaceToTransducer) {
+      return nmea.toSentence([
+        '$IIDPT',
+        belowTransducer.toFixed(2),
+        surfaceToTransducer.toFixed(3)
+      ])
+    }
+  }
+}