Rectangle corner extraction in JavaCV with source

[jviolette123]

This is great.

Here is our latest version. It has gone through a number of iterations.
We now have a full system that can run on an on-board co-processor. The algorithm needs some fine tuning, so your post came at a great time.

Launch using VisionSystem.main().

We have hard-coded values such as team name, resolution, camera ip address, and frames per second.

The system includes
- a batch file that can launch from a startup folder. We have a windows service wrapper that works on a laptop, but does not work on the embedded coprocessor, due to dll loading issues.
- an auto-reconnect feature, so that the program can re-establish connection to the camera automatically.
- a frame grabber from the on-board camera (mjpeg).
- configurable resolution and frames per second settings. These are hard coded in the constructor calls, but could be externalized.
- integration with the network table, so results can be sent back to the cRio. Note: the NetworkTable has a subtable feature, but we found that the internal table id assignment approach lead to runtime errors. We only use the top level table, named 'SmartDashboard'.
- Auto-sharpen feature, which changes the HSV settings if the system does not detect a rectangle. We found the reflection SV values changed significantly as the robot moved from 8 feet to 21 feet.
- Auto-viewport feature to handle multiple rectangles in the view. We pull in the sharpened bits, find the x-center of mass, and find the vertical bars within +/- 167 pixels. The vertical bars are reliable indicators for the backboard. Then we find the tops of the middle 4 vertical bars, which give us a bounding box for the actual top rectangle and run our rectangle detection code on that.
- An http server in the application, so we can use a browser to view internal status values.

We ended up moving away from the internal cv* functions because the hoop got in the way of the bottom bar. This kept the system from detecting the full rectangle. It may be that the approach we followed is too slow, so we may end up using your approach.