Kite Aerial Photography

The Ricoh Theta S camera produces equirectangular jpeg images of size 5376 x 2688 pixels. Since the camera simply hangs upside-down from the kite string, the resulting equirectangular images are not only upside-down (i.e. the sky is down), but the horizon is also wavy because the camera swings quite freely. A sample image from the camera is shown below.

In order to straighten the horizon and rotate it upside down we wrote a small code in python. Our python code uses pyEquirectRotate which can apply yaw, pitch, or roll to an equirectangular image based on the convention shown below:

Based on these tools/conventions, the process for straightening out the photos is as follows:

   (1) Whatever be the orientation of the camera, first apply a 'yaw' such that either the lowest or the highest point of the wavy horizon is on the central meridian.
   (2) Then apply a 'pitch' such that the horizon on the central meridian is now on the equator as well.
   (3) Rotate the image 180 degree.

Our code is available here.

The above process should technically straighten out the horizon. However in real life some waviness still remains occasionally, which is likely due to imperfection in stitching/blending together the two individual fisheye images. The image from above, when straightened using this process outlined above, results in the image shown below:

This page is maintained by Dipankar Maitra. Last updated: October 17, 2022