Time required for an accurate fix

[hatman]

Hi,
Attempting to improve my geotagging experience as I'm seeing a lot of the same incorrect or home location being tagged to photos taken elswhere. I think I understand now how that part works (including the up to 60 minutes of previous location if no new location is found).

My question now is, how long does it take for the card to "see" wi-fi networks and hotspots to get a "fix"? I found that usually when taking pictures I turn on the camera, snap a picture but do not turn it off immediately. Some times just letting it to auto-shut off. The next time I take a picture I just press the shutter button to wake it up and usually pretty much immediately take a photo right after that. However I may have moved to a different location since the last time it turned off. Could this be the reason for inconsistent geo-tagging results where pictures have the locations of a previous picture assigned? Is is that I'm not giving it enough time to get a "fix" before snapping the photo?

If so how long should I wait before taking a photo to ensure that the card has found and identified a router?

Thanks!

[hyachts]

If I understand what Berend was saying in this thread:
viewtopic.php?f=3&t=626
the fact that you let the camera power down on its own should give it plenty of time to find a fix. Apparently if a fix is not available right at the time of capture (which, as you say, is possible if you're snapping a shot right as the camera wakes up - it probably takes a few seconds at least for the card to do a scan) the card will look for a good fix for up to 60 minutes both before and after the picture was taken. Presumably it takes the closest data in time, so if you power up the camera and snap a picture immediately but the card doesn't find wifi networks for another minute or so, it should still use that data to tag the picture. The only way that would not happen is if the picture gets transferred before the card finds Skyhook-mapped APs to tag it with - or if no wifi data is found for the next hour. So for a given picture, any time the camera is powered on for up to 60min after capture the card could be grabbing wifi data for it (if it hasn't already gotten it).


What I want to know, and maybe Berend will be kind enough to enlighten us all some more, is when this assignment of wifi data takes place. Does the card tag a photo with the first wifi data it finds in that 60+/- window as soon as it finds it, or does the manager perform this "search for closest succcessful wifi data up to 60 min before and after" at the time of upload? I think it must be the former. The latter would require the card to store a comprehensive list of all APs seen whenever it is turned on. That would, however, allow the manager to, instead, perform a "search for the closest successful Skyhook-mapped wifi data up to 60 min before and after" routine rather than the card dumbly applying the first wifi data it finds with no regard for whether that data could result in a fix.

[hatman]

OK - this is interesting. I read the post you referred to and am a bit more clear how this works now.

Here is an interesting scenario though: We live in Michigan, while driving on I-75 crossing the border from Kentucky to Ohio my wife snapped a photo of the "Welcome to Ohio" overhead road sign. So from the border of KY and OH to our home it takes about 4.5 hours (without stops). When uploadign the images at home the geo tag for that image is our home AP.

If I understand this correctly the 60 +/- window into the "future" counts only while the camera is on - is this how it works?

[hyachts]

OK - this is interesting. I read the post you referred to and am a bit more clear how this works now.

Here is an interesting scenario though: We live in Michigan, while driving on I-75 crossing the border from Kentucky to Ohio my wife snapped a photo of the "Welcome to Ohio" overhead road sign. So from the border of KY and OH to our home it takes about 4.5 hours (without stops). When uploadign the images at home the geo tag for that image is our home AP.

If I understand this correctly the 60 +/- window into the "future" counts only while the camera is on - is this how it works?

That is an oddity - you didn't bring your router with you, did you?

Yes, the 60 minutes on either side only works if the camera was/is on so the card can scan for wifi during those times. It doesn't have to be on continually, though - any "on" periods in that window would be used.

[hatman]

Yeah - be my own mobile AP No, sure did not.

My question is though whether the 60 minutes are counted during the "on" time vs. the actual time passed.

For example The card got an AP fix at 4:20PM, stayed on for 5 minutes there after (did not get a new AP fix), was turned off, then 20 minutes later was turned on again, stayed on another 5 minutes (did not get a new AP fix), was turned off, then 35 later was turned on again for 5 minutes (did not get a new AP fix).

In the above scenario, when did the previsous AP fix expire:
1. On or around 5:20PM
OR
2. Has not yet expired because the "on" time total is only 15 minutes

Based on what you are saying it's the answer #2 - is that correct understanding?

[hyachts]

Yeah - be my own mobile AP No, sure did not.

My question is though whether the 60 minutes are counted during the "on" time vs. the actual time passed.

For example The card got an AP fix at 4:20PM, stayed on for 5 minutes there after (did not get a new AP fix), was turned off, then 20 minutes later was turned on again, stayed on another 5 minutes (did not get a new AP fix), was turned off, then 35 later was turned on again for 5 minutes (did not get a new AP fix).

In the above scenario, when did the previsous AP fix expire:
1. On or around 5:20PM
OR
2. Has not yet expired because the "on" time total is only 15 minutes

It goes on clock time, not elapsed scanning time (at least, all my experiences would indicate that's the case). So that wouldn't explain your 4.5 hour lag. Not sure what happened there...

[hatman]

OK - well that would make more sense. It's just that I have a series of photos taken on the road while in KY as well as while in OH and they all have my home AP as the location.

Perhaps someone from Eye-Fi would be interested in taking a look at the logs to find out what happened. I'm open to providing any info that would help in determining the cause for this oddity.