overhead camera, what kind works with ROS?

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Your question is rather vague and doesn't have enough details. What do you mean by precision? What kind of tracking? What's your desired framerate? Is color important? What resolution? Field of view? Etc.

First, you should take a look at the list of existing camera drivers for ROS. There may be other drivers out there. We've had good luck over here with Allied Vision cameras, and they have quite a few to choose from.

Second, I think you will and should be basing your decision on your application requirements. Yes, you will save time if the camera is already supported, but you can always write a ROS wrapper for a camera. You can't add new features to a camera.

Short version: see what Allied Systems has to offer, and then choose your lens appropriately.