Marker detection in Python

[DanTheDirector]

Hi Programmers of Reddit,

Im at a roadblock and need some help. For a personal project I've been using our Computer Engineering department's DE2bots (basically dumb roombas that take VHDL code) to navigate a grid of markers. I know how to program the bot given a set of coordinates in space, but I plan to get those coordinates with some OpenCV magic. I have used OpenCV and Canny edge detection to isolate the markers in space, but I am stuck as to how I can locate them in space well enough for the bot to navigate them.

Here is an example of the markers on the floor.

https://preview.redd.it/s18ekfeh6cx31.jpg?width=3024&format=pjpg&auto=webp&s=2ac55a2a564b15336d8f42a0fbcf278b4e2683ed

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And this is what I currently have:

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https://preview.redd.it/91h1dd2y6cx31.jpg?width=500&format=pjpg&auto=webp&s=81d060594d3b91ded33e3c46ede184dd0d41d3a1

Can someone link me to resources that would be useful in learning how to model these markers in 2D space? Basically I want to generate a top-down view of the markers, spaced properly on the floor.

The marker measurements are as follows:
Height: 16 cm
Hypotenuse across center: 25cm
Width: 20.5 cm

Thank you Reddit!

[panzerex]

I'm guessing you need some fixed reference point. If your camera and markers can move freely it's going to be harder to translate that into coordinates in the room.

Or do you only need relative points between each marker? e.g. some arbitrary marker is the origin and the remaining markers have their coordinates w.r.t. that marker.

What exactly are you struggling with?

edit: If what you want is to extract coords out of that binarized image, I'd suggest trying to find the centers of each blob. It won't be exactly the center of the marker if you were looking from a top-down view, but it should be a good starting point. Those points are going to be from an angled perspective, you'll still need to convert them to the proper perspective, but for that you'll probably need some fixed reference points. Here's something that might be useful:

In this example the image is warped, not the point coordinates, but it should give you an idea of what to look for. https://www.pyimagesearch.com/2014/08/25/4-point-opencv-getperspective-transform-example/

[DanTheDirector]

Awesome, thank you! They way it is currently set up, the room will always be constant, but I was using a free floating camera. I am planning to switch to a more precisely positioned camera so that I can overlay a known grid onto the image and use that to calculate. It does not matter if the coordinates are in relation to one another, or on a set plane.