gistfile1.js

angular.module('yourModule').service('pollSvc', function($interval) {
  var svc = this;

  this.start = startPolling;
  this.stop = stopPolling;
  
  function startPolling() {
    if (svc._int) throw new Error("Already polling!");
    svc._int = $interval(poll, 3000);
  }
  
  function stopPolling() {
    if ( angular.isNull(svc._int) ) return;
    $interval.cancel(svc._int);
    svc._int = null;
  }

  function poll () {
    $http.get('state.json').
      success(function (data, status, headers, config) {
          svc.markers = data;
          // may want to keep a buffer of last X poll calls in an array instead of overwriting it every time.
      }).
      error(function (data, status, headers, config) {
          // log error
      });
  }
});