The [lat,lng] point at cumulative distance meters along the polyline,
linearly interpolated between the bracketing vertices. Clamps to the ends;
non-finite meters resolves to the start; null for an empty polyline.
cum may be passed to avoid recomputation — it MUST correspond to
polyline (same length/order); a mismatch yields silently wrong results.
The
[lat,lng]point at cumulative distancemetersalong the polyline, linearly interpolated between the bracketing vertices. Clamps to the ends; non-finitemetersresolves to the start; null for an empty polyline.cummay be passed to avoid recomputation — it MUST correspond topolyline(same length/order); a mismatch yields silently wrong results.