Angle Calculation from image of goal

[Jared Russell]

Originally Posted by Al Skierkiewicz

If you know the focal length of the lens and the size of the pickup device, you can make a calculation using trig, to determine the angle of the field of view. Once you have that, you need to know the distance to target or you can back into the distance by calculating a known target size as a percentage of the field of view. This might be a frustrating exercise since the pickup and focal length of these lenses is so small. That allows a lot of error to creep into the calculation.

There is a reason why our vision system this season uses a device that provides APIs to fetch pixel array size and focal length information from per-device factory calibration

[TheOtherGuy]

Originally Posted by Jared Russell

This can be a decent enough approximation, but there is a more correct way to do this conversion:

horizontal_angle_to_goal = atan((goal_x - center_x) / focal_length_pixels)

where:
focal_length_pixels = 
.5 * image_width_pixels / tan(horizontal_field_of_view / 2)

Are you doing linear approximation or using focal length in real life? I figure since atan approximates a line when the camera is near aligned with the goal, the linear approximation would work more or less identically with any moderate framerate. This is certainly useful if the camera isn't aligned with the robot, though!

Originally Posted by Jared Russell

There is a reason why our vision system this season uses a device that provides APIs to fetch pixel array size and focal length information from per-device factory calibration

What's your setup for both the camera and processor?

[Hitchhiker 42]

Here is some LabVIEW code that tackles this problem...

The way the VI works is it takes your current gyro heading, and does some trigonometry to find the needed gyro heading and the current distance from the goal (might be helpful if you have a certain distance range you can shoot from).

Make sure to set the constants in the code (I've commented it mostly, but the important ones are the goal target width (in feet), the camera's horizontal angle of view (in degrees), and the image width (in pixels)...
Disregard the Disabled code at the bottom.

Hope this is helpful, feel free to PM me with any questions.

[Maxwellfire]

I believe they are using a Nexus 5 with on-board vision processing

[GeeTwo]

If you've found the answer above, please disregard, but this is how we've done well:

Position the robot roughly aligned with the goal (that is, eyeball it).

Do a test launch. Note where the ball ends up, in terms of inches/feet to he left or right of the goal.

Rotate the robot a known amount (probably measured in terms of encoder counts on the left and right drive systems).

Do another test launch. Note where the ball ends up (same criteria).

Based on the two measurements above, calculate a "target point" that will result in a goal, and a "proportionality constant" to get there wif the robot is pointed somewhere else.