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Mar 21, 2013

Interpreting GPS coordinates in JPGs

We went to South Carolina to view the eclipse. I took a picture of the lake, knowing my phone would add the GPS coordinates and I'd be able to figure out where I was later. Lots of families at the lakeLots of families at the lake

The smooth sand in front of that tripod is where we hope to catch shadow bands. When we got back to North Carolina (the trip home was also an adventure!) I opened one of the images in the Linux file manager and was disappointed:

Thunar is a file manager for LinuxThunar is a file manager for Linux

No interesting data. Next I tried GIMP, and was again disappointed:

Gimp is an image editing programGimp is an image editing program

I now know the answer is there, but it is labeled wrong for the Latitude. Next I tried ImageMagick, and got close, but with some odd representation:

ImageMagick is another image processing programImageMagick is another image processing program

Now I'm close, there are nicely labeled values for both Latitude and Longitude, but what do they mean?

Lat: 35/1, 10/1, 25322/1000

Lon: 82/1, 27/1, 12095/1000

If I look at windows properties, I get a fairly clear answer, but still not in a useful format. 

Windows also displays lat/lon in the properties dialogWindows also displays lat/lon in the properties dialog

I think different cameras may use slight variations of the idea, but the answers above are showing degrees, minutes, and seconds. Google and JMP just use degrees with a lot of fraction after the decimal. So the answer for this picture

Welcome sign at NC borderWelcome sign at NC border

is computed as degrees + minutes/60 + seconds/3600. For the ImageMagick representation, it looks like

Lat: 35 + 10 / 60 + (25322/1000) / 3600 = 35.173700556

Lon: 82 + 27 / 60 + (12095/1000) / 3600 = 82.453359722

You can make a google map link like this (Note the negative sign for W 82 degrees longitude, its important!):,-82.4529224,3a,75y,78.05h,100.87t/data=!3m6!1e1!3m4!1sbrxK1rvbI0K5MmOsxFMJAg!2e0!7i13312!8i6656?hl=en

Or, from the lake picture, you can go here:,-82.8332649,921m/data=!3m1!1e3

Here's the video; the shadow bands are from 2:30 to 3:30. 

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