Google Directions Api returning 0 routes

Question

We are calling the google directions api to calculate round trip values. In general it works perfectly. I have however come across a use case where it fails to come up with any route. However when we use the js google.maps.DirectionsService version with the same origin, destination, waypoints, and travelMode it works.

The failing call is: https://maps.googleapis.com/maps/api/directions/json?origin=-33.92873,18.458879&destination=-33.92873,18.458879&waypoints=via:-33.9403,18.666731&mode=driving&key=

The response is

{
   "geocoded_waypoints" : [ {}, {}, {} ],
   "routes" : [],
   "status" : "ZERO_RESULTS"
}

Answer 1

When you use via: prefix (no stopover), it adds some additional restrictions. Particularly the U-turn maneuver is not allowed, the route must go straight forward through waypoint. If this is impossible the Directions service will return ZERO_RESULTS.

To check this hypothesis I created exactly the same request, but with stopover (without via: prefix). You can see the result in the Directions calculator:

https://directionsdebug.firebaseapp.com/?origin=-33.92873%2C18.458879&destination=-33.92873%2C18.458879&waypoints=-33.9403%2C18.666731

Indeed, you should do the U-Turn in -33.9403,18.666731 (marker B) and this is the reason for ZERO_RESULTS when you try to create a route without stopovers.

This is also confirmed in the official documentation:

Caution: Using the via: prefix to avoid stopovers results in directions that are very strict in their interpretation of the waypoint. This may result in severe detours on the route or ZERO_RESULTS in the response status code if the Google Maps Directions API is unable to create directions through that point.

https://developers.google.com/maps/documentation/directions/intro#Waypoints

I hope this explains your doubt!