Promote Systems Blog

I recently wrote a post that discussed enhancing the GPS signal acquisition and positioning precision. The bottom line was that it’s best to let the GPS unit work all the time – that would let it keep locked on to as many satellites as possible (providing maximum precision), as well as report current position without a glitch. Besides, when a GPS unit is on all the time, you won’t forget to turn it on before taking a picture. But that also means that your camera will have to power the GPS unit all the time, consequently lowering camera battery life. Let’s try to figure out how we can get the best of both worlds.

When it comes to using GPS units with Nikon platform, all GPS units that are powered from the camera battery belong to either of the following two categories:

1. “Always On” GPS

These units normally have a power switch on them, and as soon as you connect the unit to the camera, and flip the GPS power switch on, the GPS will start consuming the camera battery – even if the camera itself is turned off. If you forget to turn the GPS unit off, it will eventually deplete your camera battery. Depending on your camera and battery model, it may happen as quickly as about a day of keeping your camera in the bag with the GPS unit on.

2. “Auto Power” GPS

These units have a clever schematic that allows them to track when the camera is on and ready to shoot. Such units watch if the camera exposure meters are on, and turn themselves on and off along with the camera exposure meters. The Promote GPS is an example of an “Auto Power” GPS unit.

Alternatively, if the GPS unit has a power switch (like Promote GPS), you can flip it off, and it will make sure the GPS unit will be always off, regardless of the camera exposure meter activity. Nikon GP-1 has no power switch, and can only manage its power synchronized to the camera exposure meters.

The “Auto Power” approach provides a generous power consumption advantage over “Always On” units. It lets the GPS receiver work only when it needs to – that is, when the camera is ready to take pictures.

Nikon cameras that are capable of geotagging also divide in two categories – this is important when applied to the “Auto Power” GPS units:

1. “GPS Always ON” Cameras

These are older Nikon cameras released prior to D3 and D300. They will normally shut down their exposure meters after a user-defined timeout that normally defaults to 6 seconds… but only unless the GPS receiver is connected and active! And if a camera like that sees a GPS data coming in, it will keep the exposure meters active, therefore also keeping the “Auto Power” GPS receiver powered up all the time. It is like an interlock – the GPS cannot turn off because exposure meters are active, and exposure meters cannot turn off because camera sees an active GPS. Obviously, this is not very flexible, so Nikon came up with a solution.

2. “GPS Auto Meter Off” Cameras

These are the newer Nikon cameras, starting with D3 / D300. These cameras by default will not care if there is a GPS unit connected and active, and will shut down their exposure meters regardless of that. There is a setup menu option named just like that: “GPS” -> “Auto Meter Off” – and if it is changed from its default value of “Auto” to “Off”, this will make your camera act just like older “GPS Always ON” cameras.

In order to save the most power, it is clearly best to use an  “Auto Power” GPS receiver with a “Auto Power Off” capable camera. However, as we found out in my earlier post, flipping GPS power on and off all the time is not the best overall strategy for ensuring quick and precise positioning lock. There is even a bigger issue – if you just turned on the GPS unit after a long break, it won’t be able to lock on within those 6-8 seconds allowed by the exposure meters, and will power down without obtaining a lock. The net result is that we don’t get any satellite lock at all.

As usually, there is always a way out. A GPS receiver only needs to reliably lock on to a few satellites in the beginning – and then it will perform a hot start, which only takes a second or two. So if you got a combination of #2 GPS and a #2 camera (just like my own combo of Nikon D3 and a Promote GPS), you could use the following workflow:

1. Keep the “GPS” -> “Auto meter off” setting at a default value of “Auto” for general use.

2. If the GPS receiver was off for a long time, let it get a good lock to the satellites after turning it on. To do that, temporarily disable the “Auto meter off” feature for a 5-10 minutes. Hint: placing this option in “My Menu” in Nikon cameras will let you access it faster. Alternatively, press and hold AF-ON button or half-press and hold the shutter release button until the GPS receiver gets a good lock. This will keep the exposure meters running without minding the timeout, and let the GPS get a good solid lock.

3. After letting the GPS receiver work for a while with the GPS icon on the camera display lit solid, put the “Auto meter off” feature back to “Auto” position and keep on shooting. Eventually, camera will shut down its exposure meters, and GPS receiver will be powered down, saving your camera battery.

4. Next time you are about to take a picture, half-press the shutter release button, and – voila – the GPS receiver should be able to re-lock within just one or two seconds! Simply make it a habit to check if the GPS icon on the camera LCD is solid before taking a picture, and you will always end up with geotagged images.

If the GPS receiver seems to take a long time to re-lock, let it re-lock (check for the GPS icon go solid), then let it work for a while before powering it down. That way you will let it find and remember more satellites, and that will significantly reduce the time to re-lock the next time you want to take a picture.

The above workflow applies to all GPS units that are capable of powering on and off along with camera exposure meters. Happy shooting, and feel free to post some geotagged pictures here

In my recent post I started a series of posts about working with GPS units on Nikon platform – that post discussed compatibility issues with different Nikon cameras. Now that we figured that out, let’s talk about how to make your GPS unit do its best while geotagging.

First, a little bit of insight into what a GPS generally is. If you know that already, feel free to skip this part. GPS stands for “Global Positioning System”. This initiative has been started as far back as 1972 by US Air Force – initially, strictly for military purposes. Later in 1983 it was declared that GPS system will also be available for civilian use once it is completed, which happened in mid-90s.

GPS positioning works off a number of satellites that are circling around the globe, and are constantly sending signals down to Earth surface. There are 24 to 32 satellites in service at any given time, and each satellite has a different signal that identifies that very satellite. A GPS receiver located somewhere on the Earth receives signals from those satellites, calculates how far each satellite currently is, and then uses that information along with some tricky math to calculate its position on Earth, as well as altitude above/below the sea level. It also receives the current date and time in UTC format, and includes that information into its output. Due to the nature of the satellite signal, here comes the first and the most important rule of improving signal reception:

- GPS receiver needs a clear sky view to do its best.

Modern GPS receivers can also work off reflected signals, but reflected signal always has lower power than a direct one, so reception quality will be lower. Sky obstructions such as tall buildings, mountains, trees, or even thick clouds will all have an impact on GPS signal reception.

Ideally, a GPS receiver would only need to lock on to three satellites to pinpoint a geographic position. However, the signals travel very fast, and slightest inaccuracy in measurements leads to a rather big positioning error. Altitude calculations require even more satellites to obtain a reasonably precise altitude – normally at least four satellite locks are needed to achieve an expected precision on the altitude positioning.

Locking on to more satellites allows to calculate a better position (both horizontally and vertically), and reduce the error margin. The more satellites a GPS receiver is locked on to, the more precise position it will report. Many popular GPS receivers (including our Promote GPS) are based on a SiRF Star III chip that is capable of receiving 20 satellite feeds at the same time. In practice however, a GPS receiver put into average conditions with a clear sky view is eventually locked onto 10 to 12 satellites, which provides about as good a precision as it might get with the current state of technology.

The GPS receiver is first started, it does not know where it is currently located – and consequently, does not know where to look for satellites. This is known as “cold start”. Therefore it has to lock on to at least one satellite first, listen to what it says about where the other satellites are, and then lock on to others. This procedure takes time, and in average requires anywhere from 45 seconds to a few minutes.

Once a GPS receiver has locked to at least 3 satellites, it will normally start reporting a geographical position. However this position will be rather inaccurate until more satellites are found and locked on to. A reasonable degree of precision is obtained once GPS receiver locks on to 5-6 satellites. This may take 2-3 minutes after an initial lock. So here comes the second rule:

- To improve GPS positioning accuracy, let it work for a few minutes after it obtains initial lock upon a cold start.

Now that GPS receiver has locked to quite a few satellites, it’s time to take off and shoot some pictures. But then you turn your camera and your GPS receiver off. What happens then? Most modern GPS receivers have a short term storage they use to memorize the satellite map from the last time it has been turned on. Then, when a GPS receiver is powered back on, it uses that information to quickly find the satellites to lock on to. This procedure is known as “warm start”. A warm start is not a strictly defined term, and it normally applies when you turn your GPS receiver back on within a few minutes of turning it off.

Sometimes the receiver will be able to re-lock to exact same satellites it worked with before being turned off. This is known as “hot start”, and it normally takes 1-2 seconds only.

The more time  a GPS receiver spends turned off, the more the satellite visibility will change. Therefore, the longer the GPS receiver is off, the slimmer is the chance of getting a hot or warm start. But here comes an interesting point – the more satellites your GPS was locked on to, the bigger is the chance of relocking to at least a few of them – and as soon as it gets 3-4 locks, we are in business! So here comes the third rule:

- Letting the GPS receiver work for a bit after locking on will also speed up further satellite reacquisition after restart.

Let’s summarize the three rules we found out so far:

1. GPS receiver needs a clear sky view. Make sure it can see the sky for best results.

2. Let the GPS work for a few minutes after obtaining initial lock to improve precision.

3. Do the same if you want GPS to get back online as quickly as possible after cycling its power.

Ideally, a GPS receiver that is always on will report the most precise position – but it will also deplete your batteries faster. From the other side, turning it off means you will need to wait until it locks back before continuing to taking pictures. Of course, there is always a balanced approach that depends on your needs and current environment. In my further posts I will elaborate on how you could balance between power consumption and positioning reliability / accuracy.

This post starts a series devoted to sharing tips and tricks on how to get the best of using GPS units on Nikon platform. In this post we will find out which of the Nikon DSLR cameras are compatible with GPS units.

Nikon cameras have been compatible with GPS receivers for quite a while – to my knowledge, Nikon was the first to introduce a camera that could accept an incoming GPS signal and accompany images with resulting geotags. Other brands are slowly catching up, but so far no other professional DSLRs offer GPS-related flexibility that can be compared to Nikon DSLRs.

The first Nikon DSLR to have an input for GPS signals was D1H. It had a separate terminal for GPS connection, and this tradition has been continued in D1X. Then quite surprisingly for many, the GPS support has been stripped from the D2H. Nikon probably got enough complaints about that move – so with the release of Nikon D2Hs, the GPS support has been reintroduced, and since then it has never been dropped from the Nikon professional DSLR lineup.

Until recently the only Nikon DSLRs that could make use of GPS information for geotagging were models equipped with 10-pin accessory terminal (except D1H and D1X that used a different connector). Most users only use the 10-pin terminal for remote release, but the latter only requires 3 pins – and the other 7 just asked to be put to a good use. Nikon made what they probably thought was a wise move by getting rid of a fairly common GPS connector in D1H and D1X, and assigning a few 10-pin connector contacts for that role. The immediate result was that until relatively recently, rather few companies ventured into attempting to produce Nikon-compatible GPS receivers – simply because it required making a 10-pin compatible connector, which is anything but common. Nikon’s position was clear – we want to make extra money by making all accessories in-house vs. letting others ride that train. Well, it didn’t really work out – it took Nikon almost a full decade to come up with their own standalone unit (the GP-1), and meanwhile users had to do away with clumsy setup consisting of Nikon MC-35 cord and a (hopefully) compatible, bulky and expensive third-party receiver. I sure wouldn’t want to carry that setup around for long.

Fortunately, the 10-pin connector issue has been eventually resolved, and third party GPS units started showing up on the market. And recently Nikon made a great move by introducing the GPS support in their mid-level cameras, starting with Nikon D90 and continued with D5000. Although they invented yet another connector to feed GPS signals into these cameras (also shared with remote shutter release functionality), so the whole story about connector compatibility has begun once again.

At the time of writing this post, the following Nikon cameras are compatible with GPS:

- Obsolete GPS connector: Nikon D1H, D1X
- 10-pin terminal: Nikon D200, D300, D700, D2Hs, D2X, D2Xs, D3, D3X
- “D90 terminal”: Nikon D90, D5000.

The current version of the Promote® GPS is compatible with “10-pin terminal” cameras above, and we are working to support the “D90 terminal” cameras as well. Internally, GPS support in all above cameras is pretty much the same, but some of those cameras have extra features that may significantly affect your geotagging experience. In my future posts I will describe those features in more detail, and will give a few simple answers to questions about the following:

- conserving camera battery power when using a GPS receiver
- enhancing GPS satellite reception
- ensuring quick GPS signal reacquisition after a short break
- any other questions you might have.

Feel free to comment this post to ask any questions you want answered, and stay tuned

Some customers ask us what software could they use to make better use of the Promote GPS. Internally we mostly use Google Picasa web albums and its linking to Google Maps, but there are alternatives. The following software applications support geotagging:

- Google Picasa, Windows, Mac (looks like it requires iPhoto application to be installed on Mac)

- Nikon ViewNX:

Nikon ViewNX 1.3.0 for Windows

Nikon ViewNX 1.3.0 for Mac

Latest versions can be found here.

- iPhoto (Mac)

Flickr also supports geotagging for uploaded images (more information can be found here).

There is also an application I happened to write after coming back from a trip where I tested a pre-release version of the Promote GPS. It fills in the images that were not geotagged due to an operator’s mistake (such as not turning the GPS unit on). Click here to read more about it, or go straight ahead to download page for the Promote Geotagging Suite.

UPD: Looks like I forgot to mention Adobe Photoshop / Bridge – they are certainly not primarily geotagging applications, but will let you pick geotags out of your images.

If you happen to come across another application or service that supports geotagged images or otherwise helps when working with a camera GPS, feel free to let me know. Happy geotagging