如何使用google maps api获得精确的位置？

Question

I'm trying to show the user's current location on map. Using the HTML5 geolocation it asks the user for permission, which I find annoying and I found I could bypass this by using directly the google maps api.

The problem is that with either solution the accuracy can be well off (300km off).

HTML5 solution

https://developers.google.com/maps/documentation/javascript/geolocation

This is the example that google provides and it is well off. Also the accuracy changes from browser to browser.

Google maps api solution

This is the code I've reached to.

function calculateZoomLevel(accuracy) {
    var equatorLength = 40075004; // in meters
    var mapWidth = 480; // in pixels
    var metersPerPixel = equatorLength / 4096;
    var zoomLevel = 1;
    while ((metersPerPixel * mapWidth) > accuracy) {
        metersPerPixel /= 2;
        zoomLevel++;
    }
    return Math.min(zoomLevel, 17);
}
function initMap() {
    var coords = new google.maps.LatLng(37.990832, 23.70332), accuracy = 0;
    $.post('https://www.googleapis.com/geolocation/v1/geolocate?key=MY_API_KEY').done(function(e) {
        coords = new google.maps.LatLng(e.location.lat, e.location.lng);
        accuracy = e.accuracy;
        map = new google.maps.Map(document.getElementById('map'), {
            zoom: calculateZoomLevel(accuracy),
            center: coords,
            mapTypeId: google.maps.MapTypeId.ROADMAP,
        });
        new google.maps.Circle({
            center: coords,
            radius: accuracy,
            map: map,
            fillColor: '#ff0000',
            fillOpacity: .5,
            strokeColor: '#ff0000',
            strokeOpacity: .5
        });
    }).fail(function(e) {
        console.log('fail ajax post geolocation', e);
    });
}

The thing is, I know the precision can be quite good (10-30 meters), since at the same time and on the same browser I see myself somewhere totally off on google's example, I see myself at my spot in the normal google maps page.

Answer 1

So if you don't want to capture and calculate most possible position at the cost of a lot of requests or you don't want to make your own script to connect to this api which would be a challenge... Create a looping threshold. Recall your function if it is not a reasonable accuracy. Meaning:

   coords = new google.maps.LatLng(e.location.lat, e.location.lng);
   accuracy = e.accuracy;
var c = 0;
if (c<20){
     If (accuracy <100){
         .. do your stuff..
     }else{
         initMap();
         c++;
     }
}else{
     ...failed....
}

So word to the wise... This will increase your requests in obvious ways. You have been warned..... Unless google allows unlimited requests for free when you read this.