Getting coordinates of a device in a 3d space

Question

I want to make a device that knows itselfs x and y coordinates in a 3d space, for example in a room. I can move the device anywhere in the room but I just need x and y coordinates. Is there anyway doing this by using accelerometers and/or gyroscopes? If not what is the easiest way to do this?

--Edit--

Here is the details. The device will be a kind of electronic pen. When I draw something to the wall with that device, I want it to be drawn in my computer screen too. The wall size is fixed. So, can an IMU give me the accurate coordinates on the wall during a few hours drawing period. If yes what should the precision or sensitivity of the IMU has to be?

Answer 1

I actually published a paper on this a couple years back. It is indeed difficult to track objects indoors with an IMU. As mentioned here previously, the only practical way to do it is with updates. I used passive RFID tags to update the position of my very low cost IMU (less than $100 prototype). The IMU works for short periods accurately but will begin to drift, all it needs is to occasionally pass near an RFID tag that has a unique ID and location associated with it. At that point not only do you know your current position, you can perform an affine transform on your previous path to get a more accurate picture of where you were. Your question is a bit vague on your application (I was tracking humans), but perhaps this dead reckoning with RFID fiducial updates would work for you. The paper is called "Indoor localization using pedestrian dead reckoning updated with RFID-based fiducials" if you'd like to look it up. It may give you some inspiration for your own method at least.

Answer 2

Using nothing more than inertial measurement unit (IMU) built out of accelerometers and gyroscopes is one way to determine location, but it suffers from error in the estimated position accumulating with time. The Apollo spacecraft had extremely precise IMUs, but it still needed to receive updated position and velocity information from radar trackers on Earth, and angle measurements to stars, to navigate accurately. IMUs work great for short-term localization, but for accuracy over time, even expensive IMUs are not enough.

Somehow you need to measure your position relative to landmarks in the environment. This is commonly done using either a laser or sonar range finder to measure distances, or using a video camera to estimate angles. If you don't even know the true locations of the landmarks you are using, then the task becomes the harder "simultaneous localization and mapping" (SLAM) problem.

ROS provides several packages for localization and SLAM. I suggest browsing through some of the demos and videos to get an idea of what's possible, and what might fit your application best.

Answer 3

Get two (or more) usb webcams looking into the room from different angles, and place an bandpass filter that only lets IR (infrared) light through in front of them. Hook up the cameras to a computer and find some software that will let you grab frames as bitmaps for you to read them. This works best if you can trigger the cameras simultaneously, but if the tracked object is not moving fast, this is not required. Install either IR LEDS or passive IR retroreflectors on your device (and shine IR light on it). Since it will be the brightest dot that the cameras will see (thanks to the IR notch filters), the algorithm to track this single bright dot should not be too complicated (especially being indoors, outdoors will complicate things quite a bit (I've done this by pulsing the leds very bright in synchronism with the camera shutter, having exposure time very short, around 400us, but you don't need this)). Then develop software to triangulate the position in space from the 2d location that each camera gives you. This position can be sent wirelessly to your device, so it knows where it is at. You also need to somehow guarantee that the marker is always visible, and this can be done by placing multiple cameras and only using data from those that can see it at any particular moment.