I have bought recently Navigon for iPhone for Europe and tested this in various conditions in Czech Republic. Despite overall great ratings I was disappointed.  The GPS signal was weak and was occasionally lost. When I drive on a road that is parallel to another road than the GPS point was jumping from one to another road (curiously ! ). Even strange was behavior like driving 130km/h on highway and Navigon jumped my position to side road ! In short weak GPS hardware in iPhone, bad weather conditions, dense urban areas makes this navigation unusable, or only working on 50%. GPS first lock takes sometimes more than 10 minutes if driving fast.

Navigon software is fantastic, no question about this, but what smash the quality down is GPS hardware. Now there is a solution to improve GPS in your iPhone – Use external GPS. One solution comes from TomTom with their iPhone holder. Another one is to use your own external GPS Bluetooth module and some trick how to enable iPhone to communicate with it. Actually to enable GPS BT module to work with iPhone you will need to jailbreak your iPhone and use something like Roqy GPS  http://www.roqy-bluetooth.net/roqyGPS.html

I have bought Roqy GPS license (8 EUR), and Holux 1200 GPS (40 EUR), I have used my first iPhone (2G) with OS 3.0 Jailbreaked. You have to install MobileSubstrat via Cydia, install roqyGPS, do obscure and obtrusive license registration with 32 digits (you will get license after paying over the PayPal and waiting up to 48 hours),  turn off internal iPhone Bluetooth and switch on RoqyGPS Bluetooth stack and voila you can use this in many iPhone applications using GPS. Even Whatever map, can use it. Nice thing is that Roqy GPS behaves as ‘first-class  citizen’ on iPhone – thta is other applications on iPhone can use GPS information comming from third part devices.  It is completely transparent form userpoint of view. Nice is that iPhone 2G has no GPS support so with this RoqyGPS hack you can learn youl old appliance to the new features.

So all works fine untill you try to turn-off screen (with upper iPhone button) then in my case external GPS connection has been lost and i had to switch off RoqyBT stack and connect device again. Also  unfortunately  you can’t  use  too much  Wi-Fi with the RoqyGPS  , somehow it is blocked . After some tesitng with Navigon on my trip to Bratislava it also crashed once the application. So there is still lot of places for improvments of it, but considering this is verison 0.9 I think it works very well in cases where you have pre-downloaded maps (like in Navigon) and you do not need to often go away from the external GPS .  Also bad thing is that license for Roqy  GPS is only for one concrete iPhone hardware, you can’t move it to another iPhone (this is more restrictive than Apple Store !)

iPhone Aplication tested:

Navigon Europe:  Holux1200 works with Navigon perfectly, it is like night and day  in comparision to embedded GPS performance. When just showing map (without navigaiton where it predicts position)  it precisely shows  location of my car

OffMaps: I just get trouble downloading tiles over the Wi-fi.

Whatevermap: works fine, nice to see detailed cadastral maps precise position (HOLUX 1200 is about 3-5m precise)

Last note: the picture used above is from perspective – it looks like Holux is bigg, in reality it looks like little bit bigger flash drive…

In summary: having paid for Navigon 139 USD and experiencing poor GPS performance- it is worth to use this RoqyGPS and invest cca 50 USD for external BT GPS and RoqyGPS driver . Consider this as real reason to jailbreak your iPhone to get most of this device.  Works fine with Navigon although it is sometimes obtrusive to re-pair devices if you move away from GPS BT device or you turn-off screen.

Update: in this follow-up post here http://blog.sumbera.com/2009/11/12/comparing-iphone-gps/ you can find video of GPS performance for 3 iPhones (2G with Holux, 3G and 3GS)