alistairphillips.com

I'm using this for http://rail.0gravity.co.uk/ with a sample application available for download.

if (navigator.geolocation) {
    // Single query
    navigator.geolocation.getCurrentPosition(renderPosition, renderError);

    // Continuous
    navigator.geolocation.watchPosition(renderPosition, renderError);

    function renderPosition(position) {
        /*
         * Function to handle retrieving the results
         *
         * position.coords.
         *      latitude
         *      longitude
         *      accuracy
         *      altitude
         *      altitudeAccuracy
         *      heading
         *      speed
         */
    }
} else {
    // Geo-location is not supported - alert the user
}