private static void intersectX(MutableCoordinateSequence out, double ax, double ay, double bx, double by, double x) {
    double t = (x - ax) / (bx - ax);
    out.addPoint(x, ay + (by - ay) * t);
  }
Adds a new point to {@code out} where the line segment from (ax,ay) to (bx,by) crosses a vertical line at x=x.
planetiler-core/src/main/java/com/onthegomap/planetiler/render/TiledGeometry.java