google map api v3 center point on polyline across international date line - google-maps

Question

I'm answering my own question (hopefully for your benefit), but this is the issue:
I've created a world map with polylines (in Google maps API v3). Some of these lines span the IDL (international date line). I want to place directional arrows on some of my lines, one arrow in the center of each line. On lines that span the IDL, the arrow center calculated by averaging the 2 end points together:
(latlng1.lat()+latlng2.lat()/2), (latlng1.lng()+latlng2.lng()/2)
draws the line the opposite way around the world leaving a floating arrow on my map instead of in the center of the actual line.
I initially sought a formula for getting the reverse of the line and somehow determining which was used. But it's too dependent on the map display. I even went so far as to see if I could get the center from the end points of the line if I first converted them to pixels, but the data conversion had no effect on the outcome.
So I then thought to look for an intersect method on the polyline, passing a point to check - and if it wasn't, find the center point from the reverse line (which I believe would 180-center.lng()) but there is no intersection method on polylines. So I started looking into the bounds object, because there are some intersection/contains methods on bounds.
So here is a very simple solution for a relatively undocumented problem:
(credit for function to retrieve bounds goes to Ben Appleton, ty):
function getBoundsForPoly(poly) {
var bounds = new google.maps.LatLngBounds;
poly.getPath().forEach(function(latLng) {
bounds.extend(latLng);
});
return bounds;
}
var poly_bounds = MapAbstraction.get_poly_bounds(line);
var center_point =poly_bounds.getCenter();
and then I can pass my center_point to my marker creation tool to generate the arrow in the actual center of the line without worrying about which way it was drawn.