How to get coords between 2 points - coordinates

Question

I cannot find exactly what I'm looking for or reading google documentation I missed it, I just need a function or whatever to submit 2 point, start and end, and get X waypoint in between.
Is there some api like "www.somesite.com/api.php?start=43.12,12.23&end=44.12,12.23&number_of_waypoints=5" that return some json?
thank you!

Answer 1

First of all, this will require working with geodesics, which are the shortest lines passing through two points around the Earth, assuming the Earth is an ellipsoid. WGS84 is the standard coordinate system you will see most widely used for "latitude + longitude" coordinates, and this assumes the Earth is an ellipsoid.
To solve this problem, you first need to find the azimuth (bearing angle from north) and distance between two coordinates. The way to calculate this is by solving the inverse geodesic problem.
Once we have this distance (let's say in metres), we can divide it by n, where n - 1 is the number of waypoints we want in between the line. This gives us the distance d metres between each waypoint.
Now, we need to plot points at intervals of d metres along this line. To do this, we can solve the direct geodesic problem. This gives us a new set of coordinates after moving a given distance from a given point with a given azimuth. We can do this repeatedly to get new points moving d metres from the previous point each time. One thing to note with this is that the resultant azimuth to the end of the line from different points within the line will vary, so the destination azimuth must be obtained after each stage and used for calculating the next point.
Solving the direct and inverse geodesic problems requires mathematical formulas, of which multiple are available. However, for your PHP application, you are probably best not trying to implement these yourself, but instead use a library which can do this for you. One popular library for PHP which does this is called phpgeo.
Here's an example of how this might be implemented with phpgeo:
<?php
use Location\Coordinate;
use Location\Distance\Vincenty;
use Location\Bearing\BearingEllipsoidal;
$numPoints = 5;
$coordsA = new Coordinate(50.0, 0.0);
$coordsB = new Coordinate(51.0, 1.0);
$bearingCalculator = new BearingEllipsoidal();
$distanceCalculator = new Vincenty();
// Inverse geodesic problem
// Calculate total length of line between coords
$totalDistance = $distanceCalculator->getDistance($coordsA, $coordsB);
$intervalDistance = $totalDistance / ($numPoints + 1);
// Inverse geodesic problem
// Calculate angle to destination
$currentBearing = $bearingCalculator->calculateBearing($coordsA, $coordsB);
$currentCoords = $coordsA;
$points = [];
for ($i = 0; $i < $numPoints; $i++) {
// Direct geodesic problem
// Calculate new point along line
$currentCoords =
$bearingCalculator->calculateDestination($currentCoords,
$currentBearing,
$intervalDistance);
// Add these new coordinates to the list
array_push($points, $currentCoords);
// Inverse geodesic problem
// Recalculate angle to destination
$currentBearing =
$bearingCalculator->calculateBearing($currentCoords,
$coordsB);
}
// Print out the list of points
foreach ($points as $point) {
echo "{$point->getLat()}, {$point->getLng()}\n";
}