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

This entry was posted on Thursday, May 21st, 2009 at 6:09 pm and is filed under GPS, Tutorials. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.