Interpolate between 2 GPS locations based on walking speed

Question

Problem:

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Given two locations:

L₁ = (latitude₁, longitude₁, timestamp₁), L₂

Answer 1

I'm guessing I have to calculate some time deltas, but how do I factor in the movement speed?

At linear interpolation, in your casem you iterate between two time points, using the iteration variable t which runs from start time t1 to end time t2, with a predefined step. Asume step = 1 second, which is quite usable for your application.

long t1 = location1.getTimeStamp(); // in milliseconds;
long t2 = location2.getTimeStamp();
double deltaLat = location2.latitude - location1.latitude;
doule deltaLon =  location2.longitude- location1.longtude;
// remove this line if you don't have measured speed:
double deltaSpeed =  location2.speed - location1.speed;

long step = 1 * 1000; // 1 second in millis 
for (long t = t1; t1 < t2; t+= step) {

   // t0_1 shall run from 0.0 to (nearly) 1.0 in that loop
  double t0_1 = (t - t1) / (t2 - t1);
  double latInter = lat1 + deltaLat  * t0_1;
  double lonInter = lon1 + deltaLon  * t0_1;
  // remove the line below if you dont have speed
  double speedInter = speed1 + deltaSpeed  * t0_1;
  Location interPolLocation = new Location(latInter, lonInter, speedInter);
  // add interPolLocation to list or plot.
}