# How to estimate the position of multiple static ground targets captured from a down facing camera?

An aerial vehicle captures images of the ground using its down facing camera. From the images, multiple targets are converted from their pixel position to the camera reference frame using the pinhole camera model. Since the targets are static and there is information of the vehicle attitude and orientation, each sample is then converted to the world referencial frame. Note that all targets are on a flat, level plane.

The vehicle keeps "scanning" for the targets and converting them to the world referencial frame. Due to the quality of the camera and detection algorithm, as well as errors on the altitude information, the position of the "scanned" targets is not constant (not accurate). A good representation might be a gaussian distribution around the target true position, however it will also be influenced by the movement of the aerial vehicle.

What's the best approach to estimate the position of the targets from multiple readings? This basically resumes to a problem of noise removal (as well as outlier removal) and estimation, so I would like to know what algorithms and strategies could solve the problem. In the end I expect to implement and test a collection of different approachs to understand their performance on this specific problem.

Furthermore, this system is implemented using ROS, so if you know of packages that already do what I'm searching for I would be glad to hear. You can also cite papers on the topic that you think might be of my interest.

• I voted to close this because it's an unbounded design problem (you don't have a problem, you're just looking for advice). That said, the key phrase that I think will get you started is called structure from motion. Basically, the pixel location only corresponds to an angle based on the camera transform. You need to know angle and depth to get a real x/y coordinate.
– Chuck
Commented Jan 22, 2016 at 22:25
• The problem I need resolved is one of noise removal and estimation of multiple signals at the same time. I'm searching for help on resolving that issue, don't get why you call it an unbounded design problem. And what you proposed is actually the part that I already solved since I wrote that I already converted the position of the target in order to the world referencial frame. Commented Jan 23, 2016 at 12:23
• Can you please revise your question to include how you are currently getting measurements? The way that I had read your question, I thought you had an aerial vehicle with known X/Y/Z/$\theta$ and a camera, and with nothing else and only 1 frame you were trying to determine the X/Y/Z of ground targets, which isn't possible unless you have more information. What method are you using to determine ground coordinates? What kind of noise or measurement error are you seeing?
– Chuck
Commented Jan 24, 2016 at 0:10