Google maps API v3 Elevation Service. Measured from what?

Question

Google maps API v3 Elevation Service returns hieavailable ght or depth, but relative to what? Is it MSL (mean sea level [the average]), or real time (ie: takes into account tides)

Also I note if a elevation not on record for the location it averages the nearest four. But how far away are the four (ie: if 10klm apart the average has no meaning)

My application is for depth below water (sea level), so tide hight is important

Answer 1

The Google Maps Elevation API provides elevation data for all locations on the surface of the earth, including depth locations on the oncean floor. In those cases where Google does not possess exact elevation measurements at the precise location you request. The service will interpolate and return an averaged value using the four nearest locations. Elevation values are expressed relative to local mean sea level (LMSL).

You access the Google Maps Elevation API through an HTTP interface. Users of the Google Maps JavaScript API may also access this API directly by using the ElevationService() object.

HTTP request:

https://maps.googleapis.com/maps/api/elevation/json?locations=39.7391536,-104.9847034&key=YOUR_API_KEY

Response:

{
   "results" : [
      {
         "elevation" : 1608.637939453125,
         "location" : {
            "lat" : 39.73915360,
            "lng" : -104.98470340
         },
         "resolution" : 4.771975994110107
      }
   ],
   "status" : "OK"
}

For more information, just read the above documentation link.