add mqtt listener

mqtt/utils/position_util.js

@@ -0,0 +1,66 @@
+class PositionUtil {
+
+    /**
+     * Obfuscates the provided latitude or longitude down to the provided precision in bits.
+     * This is based on the same logic in the official meshtastic firmware.
+     * https://github.com/meshtastic/firmware/blob/0a93261c0646f93aea518cc0599e547e9dc0e997/src/modules/PositionModule.cpp#L187
+     */
+    static setPositionPrecision(latitudeOrLongitudeInteger, precision) {
+
+        // check if we should use the provided precision
+        if(precision > 0 && precision < 32){
+
+            // apply bitmask to reduce precision of position to wanted bits
+            latitudeOrLongitudeInteger = latitudeOrLongitudeInteger & (0xFFFFFFFF << (32 - precision));
+
+            // we want the imprecise position to be the middle of the possible location
+            latitudeOrLongitudeInteger += (1 << (31 - precision));
+
+        }
+
+        return latitudeOrLongitudeInteger;
+
+    }
+
+    /**
+     * Truncates the provided latitude or longitude to a maximum of x decimal places
+     * e.g: 12.3456789 with 2 decimal places would be 12.34
+     * @param latitudeOrLongitudeString e.g: 12.3456789
+     * @param numberOfDecimalPlaces how many decimal places to allow in the result
+     * @returns {*|string|null}
+     */
+    static truncateDecimalPlaces(latitudeOrLongitudeString, numberOfDecimalPlaces) {
+
+        // ensure value not null
+        if(latitudeOrLongitudeString == null){
+            return null;
+        }
+
+        // split into left and right side of decimal point
+        // e.g: -12.3456789 -> [-12, 3456789]
+        var [ leftOfDecimalPoint, rightOfDecimalPoint ] = latitudeOrLongitudeString.split(".");
+
+        // check if decimal places available
+        if(rightOfDecimalPoint != null){
+
+            // truncate decimal places to desired length
+            rightOfDecimalPoint = rightOfDecimalPoint.substring(0, numberOfDecimalPlaces);
+
+            // return modified position with decimal places, if available
+            if(rightOfDecimalPoint.length > 0){
+                return [ leftOfDecimalPoint, rightOfDecimalPoint ].join(".");
+            }
+
+            // no decimal places available anymore, return left side without dot
+            return leftOfDecimalPoint;
+
+        }
+
+        // decimal places not available, return position as is
+        return latitudeOrLongitudeString;
+
+    }
+
+}
+
+module.exports = PositionUtil;