Placing the Camera

Camera placement is important for capturing quality video of a Stunt flight. While it is acceptable to place the camera farther than recommended and capturing the entire flight hemisphere, it is generally preferable to capture as much of the core of maneuver space as possible by placing the camera closer. This approach sacrifices the outer edges of the base; but takeoff, level/inverted flight, and landing maneuvers are not easy to evaluate in video anyway. The other maneuvers should be the primary focus of video recording.

General Procedure

1. Select a location outside the flight circle upwind of the expected maneuvers. This is typically where the contest judges stand. The correct distance of the camera from the center of the circle depends on the focal length of your optical system. Details are discussed below.

2. Deploy your tripod at the selected location. Weigh it down if possible so that it remains stable.

3. Mount the camera on the tripod. The result video must be in landscape orientation. If using a mobile device, this means that you must orient the device horizontally.

4. Adjust the tripod so that the camera height is approximately between 1.0—1.5 m (about 3—5 ft).

5. Turn on the camera and make sure it is in video mode. In photo mode the aspect ratio of the image frame will likely be different from that of the video, resulting in incorrect alignment.

6. Point the camera approximately at the center of the circle.

7. Tilt the camera upward so that there is a visible margin between the pilot’s feet at the center of the circle and the bottom edge of the frame. During this adjustment make sure that the camera is level. Most modern cameras have a built-in leveling guide—take advantage of it.

8. Pan the camera so that the frame’s vertical centerline aligns with the center of the flight circle.

When the above steps are followed, you will find that the top of the flight hemisphere is near the top of the frame in your AR videos. You will also generally find that the center of the frame points somewhat above the 45° elevation at the far side of the hemisphere. This is usually the desired outcome.

Determining Camera Distance

When you don’t know the focal length of your camera system, the camera distance must be determined by trial and error in the field. However, if you know your system’s focal length, we recommend that you use this Field of View calculator to determine your camera system’s angle of view. Look for the value labeled “Height” in degrees, in the section “Angle of View”:

Fig. 4 FOV calculator (via scantips.com).

If documentation for your lens is available, verify that your result is reasonably close to the manufacturer’s listed specifications.

VideoF2B includes a calculator for estimating the camera distance from circle center that will provide the best video coverage. To use it, choose Tools ‣ Place camera.. in the main menu:

Fig. 5 Camera placement calculator in VideoF2B.

Hint

Hover the mouse cursor over the values in the tables for detailed explanations of each value.

Enter the input values to the best of your knowledge:

• The flight radius R is the distance from the pilot’s chest to the centerline of the aircraft.

• The camera height C is relative to the flight base. For example, if the camera is 1 m above the pilot’s feet, then C = -0.5.

• Ground level G is also relative to the flight base. Under F2B rules, this value in meters is -1.50 and there should be no reason to adjust it.

• Camera FOV angle A is the maximum vertical angle of view of your camera system as determined above.

As you adjust each input value, the values in the Results table will update accordingly. The values of interest are in the row labeled Camera distance. These numbers represent the range of recommended distances for the camera. Place the camera within this range for best results.

Danger

Please be aware that the outboard wing of the aircraft extends outside the flight hemisphere, and the pilot never stays exactly in the center of the circle during a flight. Do not place the camera too close to the flight radius even when the calculated “nearest” distance value is very close to R!

Hint

You may use any suitable distance units for values of R, C, and G, just stay consistent. The default values are in meters. All angular values are always in degrees.

Important

For safety reasons, the calculator does not allow the camera inside the flight hemisphere. That is, the calculated “nearest” value of “camera distance” should never be less than the flight radius R. If you encounter a calculation where this is not true, please submit a bug report with your input values.

With the above precautions in mind, you are ready to produce Basic or Augmented-Reality videos.

For the technically inclined…

There are two criteria for camera placement.

The first may be obvious—the center of the flight circle must be visible in the FOV so that users may select it during AR processing. This is shown in the calculator diagram by extending the bottom of the FOV angle A to the point on the ground at the pilot’s feet.

The second criterion may not be immediately obvious. It is based on two facts:

1. The “camera cone” formed by the camera’s angle of view separates the AR hemisphere into two parts: the “near” and the “far” volume. Image space is represented by integers, resulting in a “dead zone” between the two volumes where the aircraft’s location cannot be determined. Whenever the aircraft passes through this zone, the motion trace generated by VideoF2B “jumps” across the boundary without any information between the two points. Note that this information is irrelevant during AR processing, but it is vitally important during 3D tracking.

2. The Overhead Eight maneuver is critically close to the “dead zone”. To minimize the chances of the aircraft passing across this boundary during the overhead eight, the calculator ensures that the point labeled as “Tangent elevation” on the diagram is never above the 45° elevation of the flight hemisphere. This criterion enforces a visible gap in video between the circle of 45° elevation (drawn in bright green) and the visible edge of the flight hemisphere (drawn in magenta):

   

TODO: an example AR sphere due to a badly placed camera (too far from circle) that results in loss of “gap”.