Adding gpsmagdir bootloader modification

Replace GPS heading with compass heading when speed is slow or standing still to avoid the heading from jumping around randomly

apps/gpsmagdir/README.md

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+TODO:
+- Add Widget
+- Add Settings
+- Test on BangleJS
+- Document settings with defaults
+- Document Widget
+- Write a summary why
+- Drop a note about compass north vs true north
+- Note that top of Bangle must point at moving direction when compass
+- Document uncompensated compass only when clock is faced up
+- Note to regularly calibrate compass before use
+- Note compass value not when NaN after calibration

apps/gpsmagdir/boot.js

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+{
+  const settings = Object.assign({
+    speed: 6, // when lower then this use direction from compass
+    compassSrc: 1, // [off, firmware, magnav]
+    resetCompassOnPwr: true, // reset compass on power on
+    tiltCompensation: true, // tilt compensation on default compass
+  }, require("Storage").readJSON("gpsmagdir.json", true) || {});
+  const CALIBDATA = (settings.compassSrc === 2) ? require("Storage").readJSON("magnav.json",1) || {} : undefined;
+
+  // execute Bangle.resetCompass() after Bangle.setCompassPower();
+  if (settings.resetCompassOnPwr) {
+    const origSetCompassPower = Bangle.setCompassPower;
+      Bangle.setCompassPower = function(on, id) {
+        const isOn = origSetCompassPower(on, id);
+        if (on) {
+          Bangle.resetCompass();
+        }
+        return isOn;
+    };
+  } // if (settings.resetCompassOnPwr)
+
+  if (settings.tiltCompensation) {
+    const origGetCompass = Bangle.getCompass;
+    Bangle.getCompass = function(argObj) {
+      const mag = origGetCompass();
+      if (!isNaN(mag.heading) && (argObj === undefined || !argObj.noTiltComp)) {
+        const d = require("magnav").tiltfix(mag, Bangle.getAccel());
+        mag.headingOrig = mag.heading;
+        mag.heading = d;
+      }
+      return mag;
+    };
+
+    Bangle.on('mag', function(mag) {
+      if (!isNaN(mag.heading)) {
+        const d = require("magnav").tiltfix(mag, Bangle.getAccel());
+        mag.headingOrig = mag.heading;
+        mag.heading = d;
+      }
+    });
+  } // if (settings.tiltCompensation)
+
+  if (settings.compassSrc > 0) {
+    const isFaceUp = (acc) => {
+      return (acc.z<-6700/8192) && (acc.z>-9000/8192) && Math.abs(acc.x)<2048/8192 && Math.abs(acc.y)<2048/8192;
+    };
+
+    const changeGpsCourse = (gps) => {
+      if (gps.speed < settings.speed) {
+        if (settings.compassSrc === 1 && (settings.tiltCompensation || isFaceUp(Bangle.getAccel()))) { // Use uncompensated firmware heading only if face is up
+          const heading = Bangle.getCompass().heading;
+          if (!isNaN(heading)) {
+            gps.courseOrig = gps.course;
+            gps.course = Bangle.getCompass().heading;
+          }
+        } else if (settings.compassSrc === 2) { // magnav tilt correction with magnav calibration
+          gps.courseOrig = gps.course;
+          gps.course = require("magnav").tiltfixread(CALIBDATA.offset,CALIBDATA.scale);
+        }
+      }
+      return gps;
+    };
+
+    // Modify GPS event
+    Bangle.on('GPS', gps => {
+      changeGpsCourse(gps);
+    });
+    const origGetGPSFix = Bangle.getGPSFix;
+    Bangle.getGPSFix = function() {
+      return changeGpsCourse(origGetGPSFix());
+    };
+
+    // Enable Compass with GPS
+    const origSetGPSPower = Bangle.setGPSPower;
+    Bangle.setGPSPower = function(on, id) {
+      const isGPSon = origSetGPSPower(on, id);
+      Bangle.setCompassPower(isGPSon, "gpsmagdir");
+      return isGPSon;
+    };
+  } // if (settings.compassSrc > 0)
+}

apps/gpsmagdir/metadata.json

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+{
+  "id": "gpsmagdir",
+  "name": "GPS Compass heading switcher",
+  "shortName":"GPS/Compass direction",
+  "icon": "app.png",
+  "version":"0.01",
+  "description": "Replace GPS heading with compass heading when speed is slow or standing still to avoid the heading from jumping around randomly.",
+  "type": "bootloader",
+  "tags": "outdoors",
+  "supports": ["BANGLEJS","BANGLEJS2"],
+  "readme": "README.md",
+  "storage": [
+    {"name":"gpsmagdir.boot.js","url":"boot.js"}
+  ],
+  "data": [{"name":"gpsmagdir.json"}]
+}
+