iPhone built-in GPS : a formidable accuracy !

You've probably heard the song Helmut Fritz "It annoys me" ? She will dance to many vacationers this summer campsites and beaches. Well me, what irritates me, is the disbelief of a number, still, about iPhone GPS accuracy. Isn't it stupid, isn't it ?

I have performed a few days ago a small experiment, during a call in the charming little harbour of Saint-Vaast-La-Hougue. In arrival, berthing at high tide alongside the north end of Grande Jetée, where fishermen are often moored awaiting. You can see on the screenshots below my position with my iPhone 3G. The pier is 4 meters wide along its entire length (360 m.). Note the green dot in the center of the position icon, which is the exact location provided by the GPS. You can see that iNavX app displays an horizontal position error (HPE) calculated by the GPS 17 meters. The actual position is in a circle under 3 meters diameter.

grande jetée

Berthing at the end of the Grande Jetée, under the lighthouse. Position iPhone 3GS.

I said that the network connections (Wi-Fi/3G) were cut so as not to interfere with GPS location. I then headed off along the pier to position myself on the waypoint, created last year, which marks a ladder placed at the base of an area stranding docked perfectly clean to careen at low tide. Placed on top of the ladder, I am on the following images 1m50 away from the waypoint.

grande jetée

A vertically above the scale, position dot is 1.50m off waypoint.

You may also find that, since the recent versions of IOS and iNavX, course speed (SOG) is now displayed from 0,5 knots. Last year, up to 3 knots SOG was not displayed ! Otherwise, GPS chipsets in iPhone 4 and iPad 1 and 2 are even better than the 3G.

I hope this little demonstration will eventually convince the skeptics. And if by chance you are driving your bow in the Cotentin, do not miss a call in Saint-Vaast, les huitres y sont fameuses et Mme Fleury vous réservera un excellent accueil à « La Marina » 🙂

St Vaast La Hougue

Related Articles :
iPhone built-in GPS : some details
iPhone 4 : location componants
iPad 3G, Initial information about built-in GPS


8 Replies to “Le GPS de l’iPhone : a formidable accuracy !”

  1. I tested the Iphone (Iphone 1 3G) and during iNavX 5 wet days, on a Tricat 23, 5. L’Ipad, protected by a waterproof pouch Dripro, hung by the strap of the pouch to protect the hood down, in portrait. It was the only car navigation tool, outside edge of the compass (I was obviously the scope of our paper maps navigation, they are not out of the bag). A few points deserve attention :

    – Think imperative to lock the automatic switching to landscape mode.
    – Self-surprising : after 12 hours of sailing around Belle Isle, there was still 33 % Battery charge ! (Think about putting WiFi, Bluetooth and 3G off)
    – Beautiful sea, Handling is incredibly easy (30 seconds are enough to change a road made impassable after a wind shift)
    – When the ship starts to drizzle crew and equipment, things get complicated : fingers dripping wet on a display screen provide answers fanciful ; therefore predict sponge, towel and cloth, possibly a pair of waterproof gloves.
    – The accuracy is pretty amazing (the circle of uncertainty has little more than a meter radius!).
    – In the absence of WiFi connection, iPhone owners 4 can use their 3G chip for GRIB files, manipulation to make the call, dry and calm.
    – Special mention to AyeTidesXL,more essential for peace of mind Beaches.

    In short, un outil qui fera la joie de tous ceux qui veulent naviguer « électro » sans avoir d’installation électrique à bord.


    1. Thank you for this feedback in navigation particularly wet. On this type of boat, the waterproof case de Andres Industries, despite its price, would be quite justified.
      Ce commentaire pourra achever de convaincre les plus sceptiques 🙂

  2. We used a 1-3G Iphone with Navionics mapping during our recent sailing from Puerto Natales to Puerto Williams in Chilean Patagonia.
    In addition to ease of use that is not to describe, we were impressed by the accuracy of GPS, and also that the mapping, in many cases, was better than CMap installation of board and other maps used on PC.
    Installation on board: SIMRAD mapping with CMap, Desktop PC hard NICE 3150 XP Pro SP3 with MaxSea 12.6, Scannav 10, Ozi Explorer maps and Open CPN with raster or vector according to sources. GSP Simrad and Furuno GP32. Mux AIS Shipmodul.
    Consequences: purchase of two Iphone 3G and a MBP 15″!
    For the record, we completed a stage with the only Ipad and paper cards after a planted XP, which required the relocation, CMap mapping and too quiet.
    The Iphone has its place in our opinion to our board (sailboat 43″) and its use in the cockpit in waterproof case will be very appreciated as repeater desktop PC.
    Congratulations for your site I found recently, and shame is the journalists who shamelessly looted sites without citing the authors.

  3. I used this summer on a iNavX iPad 1 wifi, connected to a small Bluetooth GPS. Just jailbreak iPad and it works perfectly. Surprise, must leave the wifi turned on the iPad (without network) otherwise it does not recognize the GPS position. Several tests, with Navionics iPhone, a standalone Garmin GPS and maps SHOM, Magellan GPS fixes and maps in WGS84, lines and corrected probes have shown the relevance of the solution. And we realize that the only uncertainty is sometimes a lack of accuracy of the maps !
    The IPAD with ten hours of battery life, small footprint, his side supports and forget’ advantageously replaced the laptop just waiting to wallow in it moves a little and still threatening to crash when it should not be…
    INavX is a bit expensive but worth it, although improvements in the economy would be welcome.
    Précision quant a la navigation, was on the other side of the tip of the Cotentin, in the Channel Islands, where the maps are accurate enough to engage in this kind of comparative tests.

  4. East – it possible for a wifi ipad exploit this excellent GPS signal from an iphone has located near by Bluetooth or WiFi without any equipment ? (This theme has already been addressed may be on this blog ?)

    1. Indeed the subject came up in this post. Jean Debeze I recently sent an email exchange with Ray Rich (Developer iNavX) which confirms, screenshots in support, it works with an iPhone 4 using a GPS WiFi iPad.

Comments are closed.