Our team uses a Limelight 3 for pose estimation but we are facing a pretty big issue. When we flash it with the 2023 image we can manually modify the size of the AprilTags, when we put it to the actual value of 165.1 mm, the robot MegaPose blue (the one we are using) is pretty acurate on the red side, but, on the blue side it gives is a value of 0.6 meters (in X) off of the real value. When we adjust the size of these fiducials down to around 150 mm, then the position in X of the robot becomes the true value. Another thing we noticed is that with the 2024 image and the correct Fiducial size, the blue pole in the Web UI of the limlight is the real position whils the white one (the MegaPose) is not, it is 0.6 meters more advanced in X. Please let us know what we are doing wrong.
Why not the 2024 image?
Because in the 2024 image we cannot modify the april tag size manually. The size comes with the fmap (in the 2024 version).
You are able to manually update the fmap in a text editor, or you can upload it to the Limelight fmap editor and update there. However, if you are having to change the size of the tag, that leads me to think the physical tag may have been scaled during printing. Have you measured the true size of your tags?
Yes we have and it is the same size as the theoratical size of 165.1mm.
As I personally found out the hard way if the megapose is off and other others are correct (while looking at 2 tags) it has a tendency to mean there is a placement issue between those 2 tags relative to each other. Can you post a picture of them and the dimensions you used between them etc?
The distance between april tags 7 and 8 is 18 inches also when the robot only sees one of the april tags at once the pose estimation is way more precise (without the offset issue)
actually the 18 inches was the distance between the two markers but we just mesured the distance between the two april tags in the same format as the image you just showed and it is 25.5 inches so this may have been the issue. We will test putting them closer right now.
We fixed our april tags to the right distance (15.75 inches between the black boxes) and it works surprinsingly well. Thank you, thank you and thank you. By the way not to future viewers a difference of even 0.5 inches between the april tags makes a huge difference.