Part of the new geolocation api provides a method to get a user’s current position. In theory that’s awesome, but in practice it was returning inconsistent results. Sometimes it was accurate, other times it was off by miles. If I tried it multiple times in a row it would get more accurate, but only some of the time. The app I was working on needed better accuracy, so I tried a few things.<\/p>\n
First I tried specifying the precision parameter (by default it is set to low precision):<\/p>\n
navigator.geolocation.getCurrentPosition(centerMap, centerMap, {enableHighAccuracy:true, maximumAge:0, timeout:30000});<\/p><\/blockquote>\n
This was MUCH more accurate, but it took about 45 seconds on my iphone to respond. Not okay. I looked to another solution: watchPosition(). It basically calls getCurrentPosition() multiple times so it can narrow in on where you are if you’re moving.<\/p>\n
navigator.geolocation.watchPosition(centerMap);<\/p><\/blockquote>\n
Boom. Much better results. BUT it’s being called a lot, and I don’t want my map jumping around, I just want 1 accurate reading. I came up with the following solution:<\/p>\n
var watchCount = 0;<\/p>\n
var watchId = navigator.geolocation.
watchPosition(centerMap);\u00a0<\/wbr><\/p>\n function centerMap(location)
\n{
\nvar myLatlng = new google.maps.LatLng(location.coords.latitude,location. coords.longitude);
\nmap.setCenter(myLatlng);
\nmap.setZoom(17);
\nwatchCount++;<\/wbr><\/wbr><\/p>\n\/\/do it 2 times
\nif(watchCount>=2)
\n{<\/p>\n\/\/show current location on map
\nvar marker = new google.maps.Marker({
\nposition: myLatlng,
\nmap: map,
\nicon: ‘http:\/\/www.google.com\/gmm\/images\/blue_dot_circle.png<\/wbr><\/a>‘,
\nclickable: false,
\nzIndex:1
\n});
\n\/\/don’t need to watch anymore
\nnavigator.geolocation.clearWatch(watchId);
\n}
\n}<\/wbr><\/p><\/blockquote>\nBasically it starts watchPosition until 2 positions are returned (I mentioned earlier how the 2nd result is always more accurate than the first), then it stops following the user. I set the threshold to 2 because the success callback is only called when there is a change in\u00a0location, so if I had set it higher and the user wasn’t moving I wouldn’t get what I want.<\/p>\n