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I'm taking a series of hemispherical (fisheye) photos while I ride my bike down city streets as a part of a project to explore the structure of city street trees. I'm planning on using my smartphone (an iphone, but I could get and another if needed) since it has built in gps and good enough image quality.

Ideally the camera would be pointed straight up (zenith angle 0 degrees), however getting a gimbal to ensure this is the case is not cost effective. I know the iphone has a level (part of the compass app), that can be used to find the zenith angle. If I could know the zenith angle associated with each image (in the same way that the lat, long, and compass bearing are recorded), then I could possibly correct my images and they wouldn't have to be pointed perfectly up.

I've searched for apps that combined the data from the compass's level with the camera, but could find nothing. Any suggestions would be greatly appreciated. Maybe I just need to write my own app.

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  • \$\begingroup\$ Is the zenith angle you want a standard part of EXIF specification or is this something new that you want to add to the metadata? \$\endgroup\$
    – Emacs User
    Commented Sep 14, 2015 at 19:30
  • \$\begingroup\$ As far as I know zenith angle is not a part of exif (compass bearing, azimuth angle, is). \$\endgroup\$
    – Tedward
    Commented Sep 14, 2015 at 19:35
  • \$\begingroup\$ In that case, look into EXIFTool command line program to add new matadata. But that still leaves the first part of your need: finding an app that can record the angle for each photo much like GeoTag Pro does for all the standard GPS EXIF tags. \$\endgroup\$
    – Emacs User
    Commented Sep 14, 2015 at 20:37
  • \$\begingroup\$ Do you know if the theodolite app saves zenith (or horizon angle as they call it) with the images? \$\endgroup\$
    – Tedward
    Commented Sep 14, 2015 at 20:58
  • \$\begingroup\$ No, I don't know. Sorry. \$\endgroup\$
    – Emacs User
    Commented Sep 14, 2015 at 22:30

1 Answer 1

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The Theodolite iOS app stores the following information in the Image Description tag:

Image Description : vert_angle_deg=87.6 / horiz_angle_deg=19.3

These values are (optionally) overlaid on the image as "Elevation Angle: 87.6°" and "Horizon Angle: 19.3°".

Theodolite is clearly meant to be used in landscape orientation, taking "typical" approximately level shots (at least with respect to the horizon line). Near the zenith, I noticed wildly varying numbers for both Elevation angle and Horizon angle, even between subsequent shots that had little variation in their orientation.

I suspect the large zenith variation is not due to Theodolite's calculations; rather, it is probably due different relative proximity to metals/magnets in my ad-hoc informal testing.

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