GPS Accuracy

[rcolman]

GPS in a dSLR is critically important to me. I photograph archaeological sites and location is really important. In fact, I bought a 6D just because of the built-in GPS.

I am not wild, however, about the accuracy. I am usually outdoors with a clear view of the sky, but still see that points wander about when they should be at a single point.

I wonder if the GP-E2 is more accurate and REPEATABLE than the built-in 6D GPS? 

Rick

[MHampton]

Or even, if you have the built in, as with the 7DmII, can you even use the external? They may not work together.

[jrhoffman75]

Updating my posting: .http://www.learn.usa.canon.com/resources/articles/2012/eos6d_inside_gps.shtml

I stand by my earlier comment. Your primary need is GPS accuracy; you should be looking at a high end GPS and geotagging software. There's a reason professional GPS units cost more than a 6D.

[TCampbell]

I have the GP-E2... compared to what I am reading here about the 6D and 7D II... the GP-E2 is EXTREMELY ACCURATE.

If I take a photo while standing on a street corner... it not only gets me on the right intersection, it gets me on the correct corner of that intersection.  Every single image I have checked is consistently where I recall standing when I took the shot (one might argue that I was actually standing a couple of feet to the left or right of that spot, but it's still a small margin of error to be within a few feet.  It is not off by hundreds nor even dozens of feet.)

But a few notes are in order...

GPS satellites do drift in their orbit.  Orbits are described by values we call "ephemeris" and these describe the shape of the orbit (orbits are always elliptical -- nothing technically has a "circular" orbit... it only seems close to circular).  Also the angle of the orbit, the major axis, the ascending node, etc. etc.  This is all very important becuase the unit has to calculus to determine where each satellite should be at any given moment in time.  The problem is... the satellites drift a bit.  The folks who mange these satellites update the orbital parameters (the data that the GPS needs to use to calculate the accurate position) and the GPS unit downloads the latest orbital parameters ... eventually.  

When you first start a GPS, it's using your assumed "last known" position and "last known" orbital parameters for the satellites to try to get a fix.  This fix will be "in the ballpark" -- but will not be accurate until the GPS has had time to get all the orbital ephemeris data updates from the satellite network.  If you haven't powered on a GPS for a year... this can take a LONG time.  I keep a hand-held GPS that I use on my boat and as it is an emergency back-up unit (only on-board in case the main unit gets fried when I'm a LONG way from shore) it hardly ever gets powered up.  I have to power it up a couple of times per year just to test that it still works and let it get ephemeris updates.  I've seen it take 20 minutes (no kidding) before it could finally get it's first position fix if it hasn't been used in too long.  If you last used your GPS yesterday.. it's remarkably fast.

When you first get a new camera and go out shooting... power it up and leave it powered up with a clear view of the sky for a while... preferably at least 15 minutes.  This should make sure the internal GPS gets the latest data and the position fixes should be fairly reliable IF the GPS has a relatively unobstructed view of the sky.   If you are in a city with tall buildings or in a forest... the GPS signal is going to be weak and you may be position fixes that show you a block away from your true position (this is normal and it's just how GPS devices work.)  Some better GPS antennas (like the GP-E2) have better and more sensitive antennas and will tend to get a reliable fix even in some of these marginal locations (like forests, etc.) where the signal is weak.

So yes, the GP-E2 is a better GPS.  It also includes a magnetic flux-gate compass so in addition to adding a position fix to the image data, it also adds the direction you were facing when you took the shot and it also has a data-logger so it can keep a "bread crumbs" path of where you've been (I never use that feature, but it's in there.)

[RobertTheFat]

Very interesting article, Tim.

Has anyone ever thought of having GPS units in close proximity talk to each other about where they think they are? It might help newcomers and stragglers achieve a better fix. One of those cases where two (or more) heads are better than one.

[BK_Shin]

I have GP-E2  for my canon. I think geotaging is important because it gives to the picture a lot of information.

But briefly spenking, GP-E2 is not that accruate that you thought.

GP-E2 is still small gadget to record its geometic information. In some area to need exact location info, those gedget can get over 400 satellites in space. But GP-E2 as small gps couldn't get that much.

So, you alreadly have 6D which has inner gps. Even if you buy GP-E2, you can't expect remarkable differences between them.

Thank you.

[TCampbell]

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@BK_Shin wrote:

I have GP-E2  for my canon. I think geotaging is important because it gives to the picture a lot of information.

But briefly spenking, GP-E2 is not that accruate that you thought.

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I'm not sure what you consider "accurate" but as I browse through my photo history of shots taken with the GPS on the camera... the overhelming majority of these shots are tagged to within just a few feet (maybe 5').  Just occasionally I will find a shot that has my position info off by perhaps 10-12', but that's (a) unusualy and (b) I only have the GPS acquiring a position fix update once every 30 seconds and it's entirely possible that I happened to catch shots where I walked a few feet within that 30 seconds.  

If you want a GPS to measure the movement of tectonic plates (need to measure fractions of an inch) then no.. it's not that accurate.  But if you want a GPS for geotagging photos to recall your location when a shot was taken... it's amazingly accurate.

I can post a few examples with EXIF data and you pull up the locations on a map if you'd like.  I have numerous images in which a Google satellite view will let you see what I was shooting, you can look at the subject in the photo, and you can tell that it pretty much pegs me spot on where I was standing at the time.

I have not used the built-in GPS on a 6D or 7D II, so I cannot compare.  But I have numerous GPS units for cars, bicycles, boats, and cameras, and this unit is one of the more accurate GPS units I've used.  I think it would be unrealistic to expect a higher degree of accuracy than the GP-E2 can provide without getting into commercial/industrial grade GPS units which wouldn't be in this price range.

[rcolman]

Can you verify that the external gps records camera direction within the image exit datA? If so, in degrees or ? Super important to me. Tnx.

[jrhoffman75]

Yes. See page 20 of user manual.

[TCampbell]

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@rcolman wrote:
Can you verify that the external gps records camera direction within the image exit datA? If so, in degrees or ? Super important to me. Tnx.

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The GP-E2 does have an internal flux-gate compass and records the direction you were facing in degrees ("magnetic" bearing, not "true" bearing.  To convert to "true" heading you would have to know the magnetic declination for your position (which is easy to look up.)

Electronic compasses generally are not particularly accurate -- they'll give a bearing which will be within a handful of degrees of correct bearing, but you can find a fixed point in the distance, check the bearing (the newer camera have a GPS-info screen so you can see it update in real-time), swing the camera off target, then swing back on target and notice the bearing info is not identical to your previous reading.  It wont be off too much... just a few degrees.  I generally regard it as being "close enough". Also, being magnetic, it can be affected by local magnetic interference.

[BK_Shin]

I think the accuracy is depend on where you take picture.

In some time, GP-E2 point exact place where I take picture. But other time, it point out of the way.

As a lot of guys mention, the accuracy is affected by many thing like, buliding nearby, number of satellite which gps can get.

As user of GP-E2, I feel strongly the accuracy is less than my iphone5.