Position Tracking Devices

I am currently in an engineering class in my senior year in high school and we are developing a device that needs to be able to track where a basketball player is on the court at any time. I have found multiple positioning devices online but can’t see if there are any devices that are exactly what my group and I would need to track a basketball player on a court. If anyone has any information for me regarding accurate position tracking systems or devices, my group an I would appreciate the help immensely. We have had the ideas to have the basketball player wearing a device on his/her wrist and be tracked or possibly use a tracking system where they would need to wear nothing in specific when playing. This is only for playing basketball alone so there would be no need to distinguish between players. Once again, any help would be greatly appreciated.

Well, seeing as how you’re tracking a human, I assume that the 2006-style vision system is out of the running. That doesn’t rule out the 2005 system, however, if you can get the calibration right. You might want to talk to some programmers on 237 or 66, both of whom had good success finding the vision tetra that season.

While not really practical if it is something you are planning on implementing for the class (as opposed to theoretical discussions), but I heard recently that the Manchester United football (soccer) club in England was taking some heat for considering GPS style implants for its players in order to track and log player positioning throughout a game.

If you remember back a few years, the TV networks began using a tracking system to follow the puck in a hockey game. That system used IR LEDs around the perimeter of the puck. Each venue was wired with receptors to determine where the puck was in a grid like fashion. With that data in hand, pan, tilt and zoom data were then extracted from each camera and processed by a computer that then positioned a “hole” in the video output of the system which was then filled and “streaked” to make the puck more visible. That system has gone on to produce the now famous “green” first down mark on football coverage. If you watch football you will notice that not all cameras will show the first down marker since all cameras are not wired to send data to the position computers.

On a FRC robot, since you don’t have access to modify the playing field, you must use encoders/gyros. As I understand this project, you would be allowed to place objects around the perimeter of the field.

Here is how I would do this project…

The player would wear a necklace, wristband, or something of that nature that contains a small IR transmitter. I believe these can be purchased/built in the sub-$20 range. I would also place 3 IR receivers at 3 corners of the court. These shouldn’t cost more than $20 a piece as well.

By reading in data seperately from those receivers, you can know the distance from that specific receiver to the transmitter. By using some basic trigonometry you can figure out where the transmitter is.

Feel free to ask for clarifications.

Are you tracking 1 player or many players?

In a simple situation of tracking 1 player, you can use the abovementioned idea. You may need multiple receivers since the IR light can be blocked by the person’s body, etc.

Where the person is can be calculated by the intensity of the IR received (since your IR transmit signal isn’t pulsed)

IF your IR transmit signal IS pulsed, you can use time-difference in recieving the pulses to calculate the position.

However it gets more complicated if you have multiple players on the field. Mary have to result to using time-synchronised microprocessors on each IR transmitter on each player.

Another thought–active RFID. I don’t know much about implementation–just brainstorming–but reading the wikipedia entry on active RFID mentions a range of up to 300 feet, can be the size of a coin, and cost a couple of dollars for the tags. Something like that could be sewn into the uniform so it wouldn’t present an injury risk like a braclet or necklace, and each player on the floor could have a unique ID for tracking the entire team or both teams.

to “track” a moving object you need to have at least two people or devices “watching” the moving object. In your case, you can track a person on a basketball court by having only two observers, since there really is no 3rd-dimension inthe game.

In such a relatively-small space as a basketball court, you can’t track the player via a technology such as GPS. But, you do have a few choices for technologies. First, the most obvious is to use radio frequency “beacons” such as cell phone that can emit a “beacon” which can be triangulate the player’s position on the field. Even easier would be to use a 900Mhz low-power belt-worn transmitter and two receivers to triangulate the player’s position. You could also do the same thing via light (e.g. lasers) but they would require “aiming” the light at the player each time you wanted to triangulate.

One other technology that may work is to use pixel-movement detection on a ceiling-mounted video camera. This is a technology that is being used in the surveillance industry.

Now…put away all of the technology and use humans as the observers. Divide the basketball court up into squares (3’x3’) and then simply “call-out” that player “A” moved from square 17 to square 22 at time 00:00:04 or something like that.

I’ve often wanted to use tracking technology to monitor where runners are within a marathon, and stock car drivers use their in-car radio system to pinpoint their location ont he track, but it’s all relatively expensive…Plus, once you get the data, how do you want to use/track the player’s movements? If you intend to keep their “traces” then you need a multi-record database to draw a map of the player’s movements.

There’s basically two ways to triangluate if you have some sort of emitter on the person and two receivers off-field. These receivers either have to be able to measure the angle (or bearing) to the player from each sensor position OR they each have to be able to measure the distance to the player. And of course the distance between the receivers and their exact location needs to be known in advance. When you talk about using RF (cell phone or 900MHz), are you thinking of measuring the distance or the angle? Measuring angle would be tricky but theoretically possible I suppose, perhaps using a highly directional antenna and sweeping it back and forth across the court. Distance would be nearly impossible. To measure distance you’d have to measure the time-of-flight of the radio signal and if you’re talking about measuring things in the range of 10s to 100s of feet you’d need extremely accurate timing. RF travels at roughly the speed of light, meaning that it travels 1 foot every nanosecond. So, you’d have to be able to measure the time of flight of the radio transmission with accuracy down to the nanosecond to be able to measure distance with about a foot of accuracy.

I suppose you could try to use signal strength as a way of estimating distance from the sensor, but that has many problems - other players blocking the signal would make the player appear father away, the difference in signal strength between 10 feet away and 20 may be too small to measure, etc.

You’d also have to contend with reflections and interference and an assortment of other problems. The bottom line is that there’s a lot of good theory to be explored in solving this problem, but a practical implementation is extremely difficult.

Hey Dave,
good dialog. I work for Harris Corporation’s RF Communications Division in Rochester NY.

Most of us in the RF world talk about “time of flight” as a way in which to determine bearing and distance to a target. basically, send out a pulse (like a bat), wait for the return signal, and determine the “time of flight” to get distance. Hopefully, you use all kinds of tricks to ensure that you’re receiving the actual signal from the player, not a reflection (multipath signal) off of something else. Each player on the court would have his/her own frequency ID, so that’s not a problem, and all players would ‘beacon’ every 500ms or so to the same set of three or four courtside receivers. A PC would do the time-of-flight calculations for each player’s signal and do the vector triangulation.

ps: I don’t know why professional sports haven;t gone to such a system to “track” a play (e.g. football playbook instead of John Madden’s chalkboard)

As an aside, I’ve often wondered if the autonomous period for robots could be improved by ‘triangulating’ the robot position off of TWO (2) light sources…but, we have enough trouble focusing-in on one source as it is… Maybe I can scrounge-up a garage business of some cheap RF beacons for bots in the future!

It seems like the easy approach to track one player on a basketball court would be a video camera looking down from the ceiling.

There are tons of video/camera inspection SW programs used in many industries, I think it should be possble to get something off the shelf that can analyze a video image stream, and track a moving object - esp since the rest of the field of view will be stationary (the floor of the basketball court).

The only place it might have difficulty is when the player shoots the ball. You might need the player to wear a unique color hat or shirt, to discriminate between the player and the moving ball.

I don’t know if there are commercial versions yet, but Dave Lavery has mentioned research in Carrier Phase Differential GPS psuedolites for local positioning. A GPS unit uses the psuedolites (specialized GPS transmitters) to determine centimeter-level accuracy within a small localized environment. As the goog (http://www.google.com) for more.

It would be helpful to know the precision requirements you are thinking of.
I am not aware of any off-the-shelf gizmo that does what you want; there probably is such a thing, you need to spend a few hours on Google.

The easiest thing to track would be a light source. Radio is directional, but not nearly as directional in such a small space as light. Also, tracking RF precisely is much more difficult than tracking a light source.

There are linear CCD sensors available - think of a camera that has only one row of pixels. An inexpensive one might have 128 pixels (1 x 128), so you can detect 1/128 of the field of view (which needs to be managed with lenses). Using two such sensors, you can triangulate (in real time) the location where the lines intersect - but at low precision at larger distances. The solution to that would be to use multiple sensors, perhaps six (one at each end plus two on eqach side - but this might have a blind spot in each corner) or even a few dozen.

The player would wear a belt (a necklace seems dangerous to me) with a small battery pack and a few LEDs of a certain color - other colors need to be filtered out of the sensor’s incoming light. (IR is probably the easiest).

Pick the sensors that report the highest brightness every (pick a time period, maybe 50 milliseconds), use a lookup table to determine the abcolute location based on the pixel value reporting highest brightness, and you have your X,Y player location.

Write back if you want to get into details, including devices.


reading this thread again, it has just occurred to me, a camcorder looking down from the ceiling will track where the player is on the court all the time, all by itself

all you have to do is look at the live video screen, or play the tape back, and the player himself will move across your monitor exactly the same way he moved around the basketball court. “There he is, there he is…”

This almost sounds silly when presented this way, but it brings out an issue with your original question. You have jumped into the middle of the engineering design cycle with this thread, and asked for help with the HOW part: How to design a tracking system

but you never told us the WHY part (the problem you are trying to solve, which will explain WHY this is needed) and the WHAT part (what the system is required to do to solve that problem).

The more you explain the WHY and the WHAT, the better we will be able to brainstorm the HOW.

An off the shelf video camera will track a basketball player on the court through the whole game, with a graphical representation of his X,Y position. Is that all you need? I get the feeling there must be more to the problem you are trying to solve.

Haha, I do think Ken is right. But, if you want to do some serious coding (It looks like the other solutions are starting to get that way), you could buy an infrared camera and track the blobs, assuming you intend to see how far they run, how faast they are, acceleration, etc… Thirty thousand lines of code later, and you can glean whatever you want.

But seriously, if you want to know how far a player runs in a game, how about a cheap pedometer? Might seem like a cop-out, but is probably more attainable before the basketball season is over.

Congrats to ken for making all of think “outside the box” and what is the actual original problem statement.

What is the actual “need” for tracking people on a basketball court?

Can the observer be a human just ‘watching’ the overhead video and drawing a player’s track on the TV screen?

Can the observer be a PC doing vector triangualtion between two radio receivers?

What’s the need?

Maybe the players can just “call out” their locations as the move.

Anyways, here’s a really cool company that uses something called ultrawideband radio transmitters and receivers on peopel (belt-worn) inside building to track their exact location at any time:

Herding cats! I had a professor, senior year at SUNY Buffalo, Dr Schmidt, who shared his Golden Rules of Engineering with us from time to time.

One was: Never design a system unless the requirements are clearly specified. Its better to quit your job than to try to design something if you dont know what its suppose to do.

If you try anyway, in the end the chances that it will happen to do what the customer really wanted are near zero. The odds are the project will be a complete failure, and you will lose your job, and you mind in the process.

Better off only losing your job.

You gotta know the WHY and the WHAT before you can invent the HOW.

My group and I need to track the movement of a player on a home basketball court, meaning it will be outside. We plan to return the ball to the player wherever he or she may be on the court. We do not need to know the distance to the player as we feel any home court is small enough to just aim the ball back to the player and let the momentum of the ball take it to the player on a bounce or two. This is only for shots that will be made and it is only for one player games. The intent is to retun made shots back to the player so he or she does not get out of rhythm when they are trying to practice and improve their shooting skills. My group and I came to the conclusion that we would need a position tracking device that works up to around 30 or 40 feet.

On an aside, thank you to all who have posted, your ideas are giving us a lot of options to look into.

The CMUCam and a fluorescent traffic vest would be a workable solution.

This ability was included in the 2004 season. Software and some documentation can be found here: http://kevin.org/frc/2004/

Are you having problems with the CMUcam?