How do I access just the gps.latitude property?

when I try this.

var arDrone = require('ar-drone');
var droneClient = arDrone.createClient();
droneClient.config('general:navdata_demo', 'FALSE'); // get back all data the copter can send
droneClient.config('general:navdata_options', 777060865); // turn on GPS

droneClient.on('navdata', function(navdata) {
console.log(navdata.gps.latitude + ', ' + navdata.gps.longitude);
// do stuff with the GPS information....
});
droneClient.takeoff(); .....

I get this error
C:\data>node gpsLog.js C:\data\gpsLog.js:8 console.log(navdata.gps.latitude + ', ' + navdata.gps.longitude); ^ TypeError: Cannot read property 'latitude' of undefined at Client. (C:\data\gpsLog.js:8:27) at emitOne (events.js:96:13) at Client.emit (events.js:188:7) at Client._handleNavdata (C:\data\node_modules\ar-drone\lib\Client.js:194:8) at emitOne (events.js:96:13) at UdpNavdataStream.emit (events.js:188:7) at UdpNavdataStream._handleMessage (C:\data\node_modules\ar-drone\lib\navdata\UdpNavdataStream.‌​js:73:10)

if I change 1 line of code I get back all gps data. I just want the latitude.
console.log(navdata.gps);