I went for a bike ride on Canada Day. Click on a bicycle icon to see what I saw.
Don’t trust iPhoto’s exported GPS coordinates
John the new jersey geographer put this better than me, but it appears that iPhoto rounds exported GPS coordinates to the nearest integer second of arc. There’s really no reason for them to do this, and it’s caused me to waste several hours tracking down why my tagged and exported photos didn’t match up.
Looking at the output data, I’m not sure if it’s to a second of arc – it appears to be rounding to the nearest hundredth minute, or approximately 0.000167°. Since GPS location uncertainty is in the fifth decimal place, this aliasing of the data is annoying.
Note: I’ve had reports that some carriers seem to disable GPS service within their service area. I’ve certainly seen slight differences as to how this works on different carriers.
Most recent camera-equipped Blackberrys have a GPS built in. One of the most handy things I’ve found for fieldwork is the ability to take pictures tagged with your location and be able to send them to contacts.
Setting this up is a little involved. First, go into the camera, and selection ‘Camera Options’. You want to enable Geotagging:
(oh, and I took the screen capture with CaptureIt). Save options, then exit back to the home screen.
I find the most reliable way of starting the GPS is to go into Blackberry Maps, and ‘Start GPS Navigation’ from the menu. Once you’ve got a reliable satellite fix (which on my old Curve, used to work fine indoors; on my Tour, not so well) you should be able see the map update with your current location, and a satellite count (9 here) on the bottom of the screen:
Exit maps, and start your camera. You’ll know if you have a location for tagging if there’s an icon that looks a bit like in the bottom right corner of the screen. With no fix, it’s a red crossed-through icon. Now take your picture!
(yeah, my Blackberry takes slightly fuzzy pictures. Dunno why.)
Metadata’s only useful if you can read it, and on anything with a command line, ExifTool works really well:
$ exiftool IMG00144-20100411-1516.jpg ... GPS Position : 43.709983 N, 79.239817 W
(one should note that without a barometric pressure sensor, GPS altitude readings are not to be trusted. This picture claimed to be taken at 120 m Below Sea Level …)
Curiously, OS X’s Preview gets GPS position completely wrong:
According to Preview, I and my bike (and my Blackberry) were close to Charyn in Kazakhstan. I’m quick on my pedals, but not good enough to get far east in an afternoon.
iPhoto gets it right, though:
Curiously, I couldn’t find anything built into Windows (okay, XP) that would read the tag location. I guess Microsoft just don’t want you to know where you are now, merely where do you want to go today.
but where am i, really?
In my first post I asked where am i? The gps in my phone said I was standing at 43.73066°N, 79.26482°W. In real life, I was standing at the junction of Kenmark Blvd and Chevron Cres.
With the Open Toronto centreline data, I can check the location of road intersections:
select distinct ( astext ( transform ( intersection ( r1.geometry, r2.geometry ), 4326 ) ) ) from centreline as r1, centreline as r2 where r1.lf_name = 'KENMARK BLVD' and r2.lf_name = 'CHEVRON CRES'
NULL POINT(-79.262423 43.730019) POINT(-79.264815 43.730591)
Hmm; three answers. NULL I can’t answer; I’ll put it down as an exhortation to Be Here Now. The second is given a clue by one of the street names: Chevron Crescent – first thing I learned when I had my newspaper round is that a crescent’s going to end you up back on the same road you started from. The last one, though, agrees to 5(ish) decimal places – well within the accuracy of my simple GPS.
Update: This query gets really, really slow on long streets. Both Chevron and Kenmark only have two road segments. Kennedy and Steeles East each have over 90.