public static Point pointAlongOffset(LineString lineString, double ratio, double offset) {
    int numPoints = lineString.getNumPoints();
    int middle = Math.clamp((int) (numPoints * ratio), 0, numPoints - 2);
    Coordinate a = lineString.getCoordinateN(middle);
    Coordinate b = lineString.getCoordinateN(middle + 1);
    LineSegment segment = new LineSegment(a, b);
    return JTS_FACTORY.createPoint(segment.pointAlongOffset(0.5, offset));
  }
Returns a point approximately {@code ratio} of the way from start to end and {@code offset} units to the right.
planetiler-core/src/main/java/com/onthegomap/planetiler/geo/GeoUtils.java