Teams using vision in 2018: why the green light?

I know that green ring lights are commonly used to track the retro-reflective targets on field elements, like the boiler from 2017 or the high goal from 2016. But I’m curious about why some teams have them this year. For example, see this gif of 1323 tracking a cube:

I remember there being retro-reflective targets on the fence, but 1323’s camera is not in a position to be useful there since it’s above the cube. So I can’t work out what it’s for at all.

It’s because RC doesn’t understand software.

It looks like the green light is to help identify where the cubes are located to have the best chance of picking them up in auto.

That gif is insane. The amount of programming for something like that…

Knowing RC, this is probably the reason.

Ive done some work with 2605 on tracking the cube for autonomous using the limelight, and it seems the green light helps distinguish cubes at different distances. When trying to target object that are yellow, sometimes it would target groups of cubes instead of just one, but mounting the camera at an angle and having the light on helps it pick them apart.

You forget about greatest coder of all time, Mr. Bob Hinkle.

The camera is probably angled downward to see the cubes.

Honestly you often see a lot of really good teams with cameras and ring lights who aren’t even using them for camera tracking and may just be using them as a camera feed in teleop or not at all. It’s pretty common to throw a camera on just in case you do find out you need to use camera tracking over dead reckoning in auto or want to add it as a upgrade later on in the season.

The color of the ring light is usually chosen to increase the contrast of whatever is being tracked. Typically when optimizing basic machine vision you’ll use a couple different simple digital filters to try to visually isolate what you want to see before the computer processes the image. While it may not look like it with the human eye it’s especially easy for a computer to isolate objects lit up with green/yellow lightingdue to a number of different factors. Green is also popular because traditionally when making a high brightness led the color green is actually cheaper/easier to produce.

While it’s not relevant this year it’s also important to remember that led ring lights are particularly common because the the 3M tape FIRST uses for vision is retro reflective meaning it returns light back to the light source. They will only glow brightly when the angle between the light source and the observer is small. This greatly increases the contrast making them very easy to isolate with computer vision. If you want to see something cool use your phone camera to look at the retro reflective tape with and without the flash on. It’s incredible how brightly it glows.

Another reason to use green is that it’s much easier to isolate from the red and blue lights on the field.

I’d be interested to hear though…how useful have top teams found vision for cube tracking in auto? We were able to get 3 cubes in the switch with only encoders and a gyro but I’d love to hear why vision still made sense for some teams like 1323.

Cubes are in set locations. You can use pathing solutions to get in the general vicinity of a cube and then use vision to more accurately pick it up. Since you know the set field location of where each individual cube is in auto, despite you using vision to move towards a cube, you know where you are, and can use pathing solutions to then move yourself towards the scoring location.

I might go out on a limb here, but it looks to me that 1323 “accidentally” picked up that thrown cube.

They looked lined up with the cube against the wall, and a program that states “drive forward until your pickup sensor “sees” a cube” would probably do this.

Knowing 1323 there is probably more things going on, however it may of been on accident.

I also notice that they use that green light to signal to human players to drop cubes out of the portal. It’s a multi functional green light.