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.