Java best way to communicate results from visions thread to a command

RowanBot · January 23, 2019, 3:47am

Looking for how to share a variable out of the vision thread.
This might be really basic, but we’ve got the critical information being calculated within our vision pipeline and out putting to the variables tab. However we’re having a hard time exposing it to our driving code.
Also curious how this might differ if we are using the rPi for vision processing.
I figure it’s going to be relatively easy to get the Pi to execute the pipeline we create, but getting the result back to the rio may be a challenge.
Just flashed by rPi image this evening and I’m sick so trying to make something useful of this lost time…
Thanks for any help.

Oblarg · January 23, 2019, 4:17am

If you’re using the rPi for vision processing and you use the image that came with WPILib this year, you’ll be using NetworkTables to communicate with the RIO. Most of the work has been done for you, here, and there are example programs to help guide you: https://wpilib.screenstepslive.com/s/currentCS/m/85074

To communicate with a separate thread in your robot application, the easiest thing to do is pass messages into a queue that can be read from your robot application’s main loop. What’s nice about this approach is that only the access to the queue needs to be synchronized, rather than the access to the messages themselves. A natural place to do this is in the callback method that you pass into WPILib’s VisionRunner:

github.com

wpilibsuite/allwpilib/blob/master/wpilibj/src/main/java/edu/wpi/first/wpilibj/vision/VisionRunner.java

/*----------------------------------------------------------------------------*/
/* Copyright (c) 2016-2018 FIRST. All Rights Reserved.                        */
/* Open Source Software - may be modified and shared by FRC teams. The code   */
/* must be accompanied by the FIRST BSD license file in the root directory of */
/* the project.                                                               */
/*----------------------------------------------------------------------------*/

package edu.wpi.first.wpilibj.vision;

import org.opencv.core.Mat;

import edu.wpi.cscore.CvSink;
import edu.wpi.cscore.VideoSource;
import edu.wpi.first.cameraserver.CameraServerSharedStore;

/**
 * A vision runner is a convenient wrapper object to make it easy to run vision pipelines
 * from robot code. The easiest  way to use this is to run it in a {@link VisionThread}
 * and use the listener to take snapshots of the pipeline's outputs.
 *

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brandon5638 · January 23, 2019, 5:40am

Agreed with Oblarg with network tables.

We’re running our vision output through a PID loop and sending the output to our drive, just like using your controller. Instead you use your vision output as your input to drive instead of a joystick input.

liavt · January 23, 2019, 4:02pm

Does someone know what the fastest refresh rate NetworkTables has in 2019? When we used it during Stronghold we found that it only updated every 100 MS which affects real time tracking performance (the RIO runs at approximately 20 MS so every 5 frames we get data.) Has the refresh rate minimum changed this year to allow for 20 MS? Otherwise we are planning on using a custom UDP server to get the performance we desire.

Anon10W1z · January 23, 2019, 4:05pm

The maximum* refresh rate was changed to 10ms for 2017 onwards.

liavt · January 23, 2019, 4:07pm

That makes our lives much easier. Thanks!

SamCarlberg · January 23, 2019, 4:29pm

The maximum refresh rate was changed to 100Hz (updates every 10 ms). The default rate is still 10Hz (updates every 100ms). You can change the update rate manually, or call NetworkTableInstance.flush() to send data immediately

system · February 4, 2020, 4:33pm