Paid: GPS Guidance w/ Haptic Feedback

Hello. I have a project that I believe can be accomplished utilizing Arduino, but I don't have the time to learn on my own before the deadline.

I would like to use an Arduino with a GPS module and app that sets a target and creates a straight line path to that target from a dynamic starting position. If the user drifts from the straight line, haptic motors would vibrate to warn the user they are getting out of line.

Would love to hear the communities thoughts on the possibility of this and anyone wanting to become involved in the project.


What deadline?

It is a self-imposed deadline, aiming for the last week of Sept. It is for a race in Oct, but I would like to have some time to train with it and work out any bugs before the event.

GPS are not super precise so the straight line is a difficult constrain to meet or even assess.

What does the terrain look like - full view of the open sky all the way?
What’s the expected speed (running or vehicle moving)?
How long is the race (battery impact or is there power on board?)
Does the race rule allow assisted orientation or is that cheating? :wink:

➜ more info required to assess feasibility

An App? On a smartphone?
Why do you need an Arduino and external GPS modul at all?
What's your budget?

I would agree with the point about more information being needed.

Its entirely possible what you are attempting to do is outside the limits of normal GPS position accuracy and repeatability.

Thanks for the additional questions.

Hoping GPS precision can be within ~5-10m. The "straight line" is a lane that is ~150m wide that competitors need to stay within. Left or right hand haptics would be triggered if competitor gets within ~20m of the left or right boundary.

  • The terrain is open sky... because the race is in the sky. :slight_smile:
  • Forward speed ranges between 150kmh and 320kmh
  • Unit will need to be battery powered. Will be powered on for ~7 minutes at a time, ~10 or so times a day.
  • The rules don't specifically prohibit such a device. We use a GPS for vertical positioning that gives us audio indicators. Looking to add the haptic as one additional level of positioning input.

Before each round of the race competitors are given a ground reference as their "target." So I would need to set the end target before each round. I was thinking a bare bones smartphone app would be easiest to use (send updates to the system via bluetooth?). But a simple app on a laptop would also work. Or if the coding is basic enough, I would be comfortable manually updating the coding for the system.

I don't know of way that a smartphone can trigger external haptic motors?

So it’s fair to say the distance is less than 50km? (At some point the earth great circle is a challenge for a straight line…)

If you get your altitude monitoring from the GPS, isn’t it only the azimuth you want to follow for a "straight line" - and thus a compass would be enough ?

It sounds as if crosswinds are a concern, so a compass wouldn't be enough.

Right good point

another point : typical GPS provide a fix per second. At 300km/h you cross 83m in 1s. If your lane is 150m wide, it's pretty quick to get within the ~20m of the left or right boundary. So might need ROM based uBlox 8 series module for example that can deliver 10 Fix/s

you haven't mentioned an external motor so far.
But my old S8 can vibrate to give a haptic feedback.
And using an OTG adapter and a small controller with USB serial, a smartphone could control an external motor also.

Sorry I did not clarify that... I will be flying and need a haptic unit in each hand gripper. If drifting left, then the left haptic would activate — if drifting right, then the right haptic would activate.

I'm not sure a smartphone is up to the task? But I admittedly am not fully aware of all the capabilities they might offer for this application.

@wildbill is correct, I am worried about crosswind (or poor configuration) drift in my flight path.

The forward speed is 300km/h, but the drift speed toward the boundary would be much slower.

May be this can get you going:

a bit of terminology

  • You start from the From waypoint and want to go to the GOTO waypoint in the most direct way (Desired Track).
  • This desired track is known as the ideal great circle path between those 2 points.
  • You find yourself in the Present Location and you want to calculate the shortest distance to the desired track, this is known as the Cross Track Distance (XTE in GPS terminology).

Here is an example:

You start near Calais and want to cross the English channel and land near Dover but on your way there you drift to A and then B. You want to know the Cross Track Distance for A and B based on their latitude and longitude.

Here is some code for this using some of the builtin functions of TinyGPS++ (and one extra function to calculate the XTE).

// formulas from
// adjusted earth radius to match TinyGPS++ value for coherence

#include <TinyGPS++.h>  //
TinyGPSPlus gps;
#define gpsSerial Serial1
const uint32_t GPSBaud = 115200;

double fromLat  = 50.95723461041729, fromLon = 1.8175379777021576;  // start point        = 50.95723461041729, 1.8175379777021576
double gotoLat  = 51.13113565835111, gotoLon = 1.3260115342823147;  // destination point  = 51.13113565835111, 1.3260115342823147

double ALat  = 50.97572382883768, ALon = 1.7230724414682619;        // point A            = 50.97572382883768, 1.7230724414682619
double BLat  = 51.12242447725161, BLon = 1.3669750943475254;        // point B            = 51.12242447725161, 1.3669750943475254

double distance;                                  // Distance between start and destination (orthodrome, hypothetical sphere of radius 6372795 meters)
double dtk;                                       // Desired Track in degrees (forward azimuth)

// Cross-track distance (XTE)
// Shortest signed distance from a point (lat3, long3) to an ideal great circle path defined by (lat1, long1) and (lat2, long2)
// Negative if to left, positive if to right of path, with hypothetical sphere of radius 6372795 meters

double crossTrackDistanceFromTo(double lat3, double lon3, double lat1, double lon1, double lat2, double lon2) {

  const double R     = 6372795.0;
  const double ad13  = gps.distanceBetween(lat1, lon1, lat3, lon3) / R;
  const double rtk13 = radians(gps.courseTo(lat1, lon1, lat3, lon3));
  const double rtk12 = radians(gps.courseTo(lat1, lon1, lat2, lon2));
  const double dxt   = asin(sin(ad13) * sin(rtk13 - rtk12));

  return dxt * R;

void setup() {
  Serial.begin(115200); Serial.println();
  dtk = gps.courseTo(fromLat, fromLon, gotoLat, gotoLon);
  distance = gps.distanceBetween(fromLat, fromLon, gotoLat, gotoLon);
  Serial.print(F("Distance to destinatinon: "));
  Serial.print(distance, 0); Serial.println(F(" m"));

  Serial.print(F("Desired Track (DTK°): "));
  Serial.print(F("° (")); Serial.print(gps.cardinal(dtk)); Serial.println(F(")"));

  double cmgF = gps.courseTo(fromLat, fromLon, fromLat, fromLon);
  double xteF = crossTrackDistanceFromTo(fromLat, fromLon, fromLat, fromLon, gotoLat, gotoLon);

  Serial.print(F("Point From: ")); Serial.print(fromLat, 6); Serial.write(','); Serial.print(fromLat, 6);
  Serial.print(F(" - (CMG =")); Serial.print(cmgF); Serial.print(F("°), "));
  Serial.print(F("Cross track distance = ")); Serial.print(xteF); Serial.print(F(" m, "));
  if (xteF == 0) Serial.println(F("on ideal course"));
  else Serial.println(xteF < 0 ? F("to the LEFT") : F("to the RIGHT"));

  double cmgA = gps.courseTo(fromLat, fromLon, ALat, ALon);
  double xteA = crossTrackDistanceFromTo(ALat, ALon, fromLat, fromLon, gotoLat, gotoLon);

  Serial.print(F("Point A: ")); Serial.print(ALat, 6); Serial.write(','); Serial.print(ALon, 6);
  Serial.print(F(" - (CMG =")); Serial.print(cmgA); Serial.print(F("°), "));
  Serial.print(F("Cross track distance = ")); Serial.print(xteA); Serial.print(F(" m, "));
  if (xteA == 0) Serial.println(F("on ideal course"));
  else Serial.println(xteA < 0 ? F("to the LEFT") : F("to the RIGHT"));

  double cmgB = gps.courseTo(fromLat, fromLon, BLat, BLon);
  double xteB = crossTrackDistanceFromTo(BLat, BLon, fromLat, fromLon, gotoLat, gotoLon);

  Serial.print(F("Point B: ")); Serial.print(BLat, 6); Serial.write(','); Serial.print(BLon, 6);
  Serial.print(F(" - (CMG =")); Serial.print(cmgB); Serial.print(F("°), "));
  Serial.print(F("Cross track distance = ")); Serial.print(xteB); Serial.print(F(" m, "));
  if (xteB == 0) Serial.println(F("on ideal course"));
  else  Serial.println(xteB < 0 ? F("to the LEFT") : F("to the RIGHT"));

  double cmgG = gps.courseTo(fromLat, fromLon, gotoLat, gotoLon);
  double xteG = crossTrackDistanceFromTo(gotoLat, gotoLon, fromLat, fromLon, gotoLat, gotoLon);

  Serial.print(F("Point GOTO: ")); Serial.print(fromLat, 6); Serial.write(','); Serial.print(fromLat, 6);
  Serial.print(F(" - (CMG =")); Serial.print(cmgG); Serial.print(F("°), "));
  Serial.print(F("Cross track distance = ")); Serial.print(xteG); Serial.print(F(" m, "));
  if (xteG == 0) Serial.println(F("on ideal course"));
  else  Serial.println(xteG < 0 ? F("to the LEFT") : F("to the RIGHT"));

void loop() {
  if ( gpsSerial.peek() != -1) {
    if (gps.encode( {
      if (gps.location.isValid()) {
        double presentLat =;
        double presentLon = gps.location.lng();
        double cmg = gps.courseTo(fromLat, fromLon, presentLat, presentLon);; // Course Made Good in degrees
        double xte = crossTrackDistanceFromTo(presentLat, presentLon, fromLat, fromLon, gotoLat, gotoLon);

        Serial.print(F("Position: "));  Serial.print(presentLat, 6); Serial.write(','); Serial.print(presentLon, 6); // print our position
        Serial.print(F(" - (CMG=")); Serial.print(cmg); Serial.println(F("°)"));
        Serial.print(F("Cross track distance = ")); Serial.print(xte); Serial.print(F(" m, "));
        Serial.println(xte < 0 ? F("to the LEFT") : F("to the RIGHT"));

Running this on an Arduino Mega, the Serial Monitor (@ 115200 bauds) will show

Distance to destinatinon: 39441 m
Desired Track (DTK°): 299.56° (WNW)
Point From: 50.957233,50.957233 - (CMG =0.00°), Cross track distance = 0.00 m, on ideal course
Point A: 50.975723,1.723072 - (CMG =287.30°), Cross track distance = -1471.01 m, to the LEFT
Point B: 51.122425,1.366975 - (CMG =300.42°), Cross track distance = 548.94 m, to the RIGHT
Point GOTO: 50.957233,50.957233 - (CMG =299.56°), Cross track distance = 0.00 m, on ideal course

the loop does not print anything if you don't have a GPS connected to Serial1 otherwise it would constantly monitor your Cross track distance.

So you know if you are left or right of the ideal path and have the distance to that path - haptic feedback should be pretty easy to figure out instead of printing.

You'll need of course to find a way to enter the From and GOTO waypoints into the Arduino as those are hardwired at the moment. From could probably be set easily with the press of a button and reading the current location but the GOTO waypoint will require some sort of User Interface.

Running on an ESP32 or Teensy would be faster due to all the floating point maths that are required. I would not advise to stick with a UNO or MEGA.

I'm totally unsure of the maths (although they look realistic in the example above) and there are approximations like saying earth is an hypothetical sphere of radius 6372795 meters for example. Flying near the poles will break many of the approximations in the formulas as well and GPS precision might not be good enough...

As a side note, I would assume most advanced GPS system would probably know how to show these information automatically and probably be more trustworthy than this code...


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