Shadow Cam

Shadow Cam.

This is a little proof of concept video I just put together. The goal is to always keep my aircraft’s shadow in the field of view.

Equipment: Senior Telemaster. Fly-Cam-One-3 with built in pan/tilt. Sparkfun 6DOFv4 IMU (it was laying around so I used it.) Gumstix flight computer. Ardupilot used for controlling pan/tilt servos on the camera.

The flight is 100% manually piloted. Camera is 100% automatically pointed.

On board I am running a 15-state kalman filter for attitude estimation. The filter converges to “true” yaw angle independent of ground track, wind, and magnetometer. This is actually critical for camera pointing.

On the ground I have small app I whipped together one evening that computes the sun location for the current time in ECEF coordinates. Then converts the sun “vector” to NED coordinates based on a GPS connected to the ground station (assuming I’m not ranging very far from my start point.) The code computes a new sun angle every minute. Finally, the sun vector is inverted to get a shadow vector and that is sent up to the aircraft as it’s target point vector (once a minute.)

Notice: sun vector * [ -1 -1 -1 ] = shadow vector.
Also: sun vector * [ 1 1 -1 ] = reflection vector (where we would be looking at the suns reflection off surface water.)
Also: sun vector * [ 1 1 1 ] = rainbow vector if we would happen to fly above the clouds (this would keep us looking at the center of a rainbow circle/arc.) 🙂

In order to run myself over with the shadow from the aircraft’s perspective I need to fly the airplane through the sun from the ground pilot’s perspective.

Disclaimers: this was my first time out trying something like this so the video is rough. The pan/tilt on the flycam is very low grade, but works well enough for a demo. I’m also flying with an IMU that is about 2 orders of magnitude coarser than I’m used to flying with, so that degrades my attitude estimation more than I would have liked (but the filter still converges.) I put very little effort into aligning the IMU mount with the camera mount, so there are certainly a few degrees of bias just from mounting issues. Finally, I only eyeballed the mapping between servo commands and pan/tilt angles so I’m in the ball park, but there are certainly errors there too. It’s a hack, but made for a fun afternoon. 🙂

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