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Outdoor tracking of three objects
Dave from United States  [8 posts]
2 years
I am planning on using an elevated view looking down on an area approximately 100ftx100ft.   I need to track at most three objects with velocity and distance relationship in just x-y plane.   I need a weatherproof camera that interfaces with roborealm...wired would be fine.  The speed will max at about 15 mph.   The objects are about 4 feet long.    I need relationship accuracy to about 2 feet.   Will one camera suffice or would I need multiple views?  Any camera suggestions?   How high above the surface would give me sufficient distance/ velocity discrimination?
Also would multiple ground level cameras be more feasible?
Steven Gentner from United States  [260 posts] 2 years
Dave,

If you are using an approximate 70 deg field of view (typical webcam .. or higher for http://www.logitech.com/en-us/product/webcam-c930e-business) then you'd need to place a single camera a bit higher than

tan(35) = 50ft / height

or

height = 50ft / tan(35)

or at about 70 ft

Its approximate since the horizontal and vertical FOV of cameras will differ slightly. You'd need to use the smaller angle to ensure you get that dimension into view.

If you use the above Logitech camera then you are looking more like 50ft due to the wider field of view. Note that the wider the field of view, typically the more distortion you will have to correct for.

The rest of your questions will depend on the camera chosen. I'm not sure if multiple ground level cameras would be more feasible as what you really need is distance moved which is ideal for an overhead camera.

If you have a HD resolution at around 720 vertical pixels (smaller resolution) then each pixel would represent about 100ft / 720 or 0.14ft or 1.6 inches per pixel. So for a 2 ft accuracy you'd be working with about 14 pixels distance between objects of about 6 to 7 pixels wide. That's not great but should be workable as long as your objects can be segmented from the background easily. If there is too much clutter on the ground segmenting a 6 or 7 pixel object is going to be very difficult esp. if they are not a single completely solid color/intensity.

In terms of which camera, start doing some online research and provide manufacturers with those dimensions (100ftx100ft) and your maximum height you can go and see what they suggest.

Given the height, I would expect a ethernet based (POE - power over ethernet) might be the way to go. A USB camera would not make it that far without signal enhancers.

You can use multiple cameras which would decrease the height but require you to merge the results in some way. Merging the images to create a single large image is possible but you'd have to make sure this calibration is somewhat static (i.e. the cameras don't move much when the wind blows) to ensure that the stitch is good between the images over time.

STeven.

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