Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2003-03-11
2004-12-14
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
Reexamination Certificate
active
06831603
ABSTRACT:
BACKGROUND OF THE INVENTION
Motion tracking, also known as Motion capture is the process of recording a live motion event and translating it into usable mathematical terms by tracking a number of key points in space over time and combining them to obtain a single three-dimensional representation of the performance. In brief, it is the technology that enables the process of translating a live performance into a digital performance. The captured subject could be anything that exists in the real world and has motion; the key points are the areas that best represent the motion of the subject's different moving parts. These points should help resolve pivot points or connections between rigid parts of the subject. For a human, for example, some of the key points are the joints that act as pivot points and connections for the bones. The location of each of these points is identified by one or more sensors, markers, or potentiometers that are placed on the subject and that serve, in one way or another, as conduits of information to the main collection device.
There are a number of existing systems that can track the motion of human, animal or inanimate subjects. Existing motion capture systems are classified as outside-in, inside-out, and inside-in systems. These names are indicative of where the capture sources and sensors are placed.
An outside-in system uses external sensors to collect data from sources placed on the body. Examples of such systems are camera-based tracking devices, in which the cameras are the sensors and the reflective markers are the sources.
Inside-out systems have sensors placed on the body that collect external sources. Electromagnetic systems, whose sensors move in an externally generated electromagnetic field, are examples of inside-out systems. Inside-in systems have their sources and sensors placed on the body. Examples of these devices are electromechanical suits, in which the sensors are potentiometers or powered goniometers and the sources are the actual joints inside the body.
The principal technologies used today that represent these categories are optical, electromagnetic, and electromechanical human tracking systems.
Optical Motion Capture Systems
Optical motion capture is a very accurate method of capturing certain motions when using a state-of-the-art system. It is a real-time process with certain limitations, such as marker count and number of performers and cameras.
A typical optical motion capture system is based on a single computer that controls the input of several digital CCD (charge-coupled device) cameras. CCDs are light-sensitive devices that use an array of photoelectric cells (also called pixels) to capture light, and then measure the intensity of the light for each of the cells, creating a digital representation of the image. A CCD camera contains an array of pixels that can vary in resolution from as low as 128×128 to as high as 4096×4096 or even greater.
Obviously, the higher the resolution, the better, but there are other trade-offs. The samples-per-second rate, or frame rate, has to be fast enough for capturing the nuances of very fast motions. By today's standards, a CCD camera with a resolution of 4096×4096 would be able to produce less than one frame per second. Another important feature is shutter synchronization, by which the camera's shutter speed can be synchronized with external sources, such as the light-emitting diodes (LEDs) with which optical motion capture cameras are usually outfitted.
The number of cameras employed is usually no less than 4 and no more than 32, and they capture the position of reflective markers at speeds anywhere between 30 and 1000 samples per second. The cameras are normally fitted with their own light sources that create a directional reflection from the markers, which are generally spheres covered with a material such as Scotch-Brite tape. Infrared light sources are preferred because they create less visual distortion for the user. The marker spheres can vary from a few millimeters in diameter, for small-area captures, to a couple of inches.
The optical system must be calibrated by having all the cameras track an object with known dimensions that the software can recognize, such as a cube or a wand with reflective markers. By combining the views from all cameras with the known dimensions of the object, the exact position of each camera in space can be calculated. If a camera is bumped even slightly, a new calibration must be performed. It is a good idea to recalibrate the system after every few minutes of capture, since any kind of motion or vibration can shift the position of a camera, especially if the studio is located on unstable ground.
At least two views are needed to track a single point's three-dimensional position, and extra cameras are necessary to maintain a direct line of sight from at least two cameras to every marker. That doesn't mean that more cameras are better, because each additional camera increases post-processing time.
Once the camera views are digitized into the computer, it is time for the post-processing to begin. The first step is for the software to try to produce a clean playback of only the markers. Different image processing methods are used to minimize the noise and isolate the markers, separating them from the rest of the environment. The most basic approach is to separate all the groups of pixels that exceed a predetermined luminosity threshold. If the software is intelligent enough, it will use adjacent frames to help solve any particular frame. The system operator has control over many variables that will help in this process, such as specifying the minimum and maximum lines expected per marker so the software can ignore anything smaller or bigger than these values.
The second step is to determine the two-dimensional coordinates of each marker for each camera view. This data will later be used in combination with the camera coordinates and the rest of the camera views to obtain the three-dimensional coordinates of each marker.
The third step is to actually identify each marker throughout a sequence. This stage requires the most operator assistance, since the initial assignment of each marker has to be recorded manually. After this assignment, the software tries to resolve the rest of the sequence until it loses track of a marker due to occlusion or crossover, at which point the operator must reassign the markers in question and continue the computation. This process continues until the whole sequence is resolved and a file containing positional data for all markers is saved.
The file produced by this process contains a sequence of marker global positions over time, which means that only each marker's Cartesian (x, y, and z) coordinates are listed per frame and no hierarchy or limb rotations are included.
Electromagnetic Trackers
Electromagnetic motion capture systems are part of the six degrees of freedom electromagnetic measurement systems' family and consist of an array of receivers that measure their spatial relationship to a nearby transmitter. These receivers or sensors are placed on the body and are connected to an electronic control unit, in most cases by individual cables.
Also called magnetic trackers, these systems emerged from the technology used in military aircraft for helmet-mounted displays (HMDs). With HMDs, a pilot can acquire a target by locating it visually through a reticle located on the visor. A sensor on the helmet is used to track the pilot's head position and orientation.
A typical magnetic tracker consists of a transmitter, 11 to 18 sensors, an electronic control unit, and software. A state-of-the-art magnetic tracker can have up to 90 sensors and is capable of capturing up to 144 samples per second. The cost ranges from $5,000 to $150,000, considerably less than optical systems. To take advantage of the real-time capabilities of a magnetic tracker, it must be connected to a powerful computer system that is capable of rendering a great number of polygons in real time. Dependin
Fulwider Patton Lee & Utecht LLP
Gregory Bernarr E.
Menache LLC
Mull Fred H.
LandOfFree
Motion tracking system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Motion tracking system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Motion tracking system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3330086