What Is 3D Motion Tracking?

Three-dimensional (3D) motion tracking is the act of capturing motion data from actors and actresses. This is similar to filming a person moving around, but the difference is that, instead of footage that can only be played back, 3D motion tracking records the movements so they can be applied to 3D rendering programs. Performing the capture requires special hardware, such as suits and tiny tracking units, but some systems just need a camera to capture the motion. A subset of motion capturing, called performance capture, deals with extremities and facial features.

The act of 3D motion tracking is similar to filming people moving around, but the difference is in how the information is handled. With filming, the footage can only be watched, while motion capture is a digital model of the motion that can be applied to 3D figures on a computer. This is most often used by the movie industry when creating 3D animated films or when computer-based models require intricate movement. Motion tracking also is used by the military to build virtual exercises and by engineers to control machines.

Special hardware is required to perform 3D motion tracking. In the past, actors and actresses were fitted with suits and small tracking units, and a camera tracked their movement. This hardware is still used frequently, but more advanced systems are able to capture motion data without the need of trackers, known as markerless tracking. A special camera is still needed to translate all movements into digital signals and information.


The practice of 3D motion tracking deals with how the limbs and torso move, but not the finer details of human movement. For finer details, performance capture is used. This type of tracking obtains data from finger and facial movements, so artists controlling the 3D model have intricate data about these movements. Without this information, artists have to create facial expressions and finger movements from scratch, which can lead to awkward expressions or stiff hands and fingers.

Before 3D motion tracking was available, animated film artists in the past used a similar system, called rotoscoping, to track motion. Actors and actresses were filmed performing movements and speaking lines according to the script. Artists would then take the film and draw over each frame individually. This resulted in more realistic animation, because all the movements were based on real people. Most major animation companies, before the advent of the 3D motion tracking, used rotoscoping.

What Are the Different Ways to Detect Motion?

A number of product types and techniques can detect motion; many are used in applications such as opening shop doors, turning on security lights and video recorders, or sounding alarms. Whether as standalone units or parts of systems or computerized networks, detectors fall into two common categories: area sensors and local sensors. Area sensors scan broad fields on properties, using techniques such as infrared (IR) or ultrasonic fields. Local sensors occupy rooms and interiors, using techniques such as lasers and light beams.

Sometimes called perimeter and space sensors, both types employ active and passive sensing techniques. Active sensing emits a constant field, while passive sensing waits in standby for an event to trigger a threshold setting. These techniques can electronically sense light, sound, heat, or vibration.

Active sensors detect motion by dispersing a continuous fan-shaped field, for example, of ultrasonic waves. The field remains static until something enters it and disturbs the reflected pattern. A disturbance may fall within calibrated tolerances or it may exceed them and trigger the control unit and alarm.

Passive sensors remain inactive until an event, such as motion or sound, exceeds a preset level. Active and passive techniques both have limited ranges that may weaken with distance. Hybrid products combine sensor types for greater effectiveness, pairing infrared with ultrasonic, for example.


Area sensors commonly rely on two methods to detect motion: passive infrared (PIR) and microwave sensors. PIR types detect interruptions to an invisible laser beam, as with automatic doors. Microwave sensors use radio waves.

Other types include ultrasonic, which relies on sound wave ripples, and video, which detects lighting changes and may activate a computer or digital cassette video recording device. Vibration sensors monitor manufacturing equipment for early detection of mechanical problems. These may rely on accelerometer technology, using gyroscopic or three-axis orientation circuitry.

Local sensors sometimes rely on disruptions to beams of IR, laser, or visible light. They can also detect motion with components that measure tilt, proximity, or strain. Pressure pads detect walking traffic, while camera detectors activate video or lights only in the presence of motion, saving power and memory. Microwave types occur primarily in security industries.

Detecting motion often requires the use of an emitter and a sensor: for example, a photodiode that responds to light, or a transducer that responds to ultrasound. A photodiode might catch photons and amplify them into an electronic signal. Fluctuations or disruptions in the emitted fields are registered and electronically responded to. These detectors are typically designed to react to large changes in their fields and beams, rather than gradual changes such as weather and temperature variations. The human element, however, is very easily mapped in infrared light and physical space, making it virtually impossible to thwart these sensors even with very slow movements.

What is a Motion Detector?

A motion detector is a device that monitors a field of view and performs a function if motion is detected within that field. The function might be to trigger the opening of a door, as in the case of a grocery store; start a videotape machine for surveillance; turn on floodlights; or sound an alarm. A motion detector might detect motion through the use of optics or acoustics and can be passive or active.

Passive infrared (PIR) motion detectors are commonly used inside homes, linked to security systems. The unaided human eye cannot see infrared light, but the human body generates an infrared signature in the form of heat. A passive motion detector does not emit signals, but monitors the temperature of the field of view looking for changes in the infrared spectrum. A human body moving through the field can trigger the motion detector to sound an alarm, call a monitoring agency, or perform another function. When used in conjunction with surveillance or security systems, motion detectors are just one part of the total system.

An active motion detector emits optics or sound waves and measures feedback to detect motion. The simplest type of active motion detector is commonly used in commercial doorways to trigger a doorbell. A device is fixed to one side of the doorway, an optical sensor to the other. A beam of light passes from the device to the sensor. When someone enters the establishment, the beam is broken, triggering the doorbell.


Another kind of active motion detector is used at grocery stores to automatically open the doors for customers. This type of motion detector emits radar pulses; monitoring the time it takes the energy to bounce back. When any object disrupts the radar’s reflection, the motion detector triggers a device that opens the doors.

Other active motion detectors emit ultrasonic acoustic waves to detect motion. Any object moving across that plane will disturb the acoustic signature and change the picture. The human ear cannot detect ultrasonic waves, but certain animals are sensitive to ultrasonic signals.

Some types of motion detectors turn on floodlights in the yard, driveway or porch when motion is detected. After a period of time with no movement, the lights go out. Some motion detectors can be set to be less sensitive to the movement of small animals.

Motion detectors can be purchased at home improvement stores and online. If you are interested in a professional home security system package, the motion detectors required will come with the system and extra detectors are commonly available. Motion detectors are inexpensive devices that can add security to a business or home and provide peace of mind.

How Do I Choose the Best Motion Tracking Camera?

There is much variety in the motion tracking camera market, which can make it hard for users to find the right camera for a job. The amount of hertz (Hz) determines how much power a motion tracking camera uses and how complex the motion data can be. Markers are often used to capture motion, and the more trackers the camera can pick up, the more precise the movements. The smallest amount of movement the camera can track and pick up will be an indication of how tiny a movement can be and still be captured, and cameras that pick up the tiniest of data will likely be best for professional data tracking. Using multiple cameras will provide a more complete field-of-view, but the motion tracking software that comes with such a camera will likely only accommodate a limited number of cameras; users should get the highest camera threshold possible.

Every motion tracking camera operates on hertz; it gives power to the camera and allows it to function. A higher hertz rating means the camera needs more power to work but also can capture more complex data. A low-powered camera will be suitable if basic data, such as walking or simple dancing, is needed. High-powered cameras can record complex action or fighting scenes and other advanced movements.


Most motion tracking camera devices rely on physical markers placed on an actor or actress. These markers convey bone and motion data to the camera and make it easier for the camera to pick up movement. The more makers the camera can use at once, the better it will pick up any movements. An alternative is a markerless camera, which does not need markers to track motion.

A motion tracking camera has to be extremely sensitive to motion, more than most other cameras. This means the camera must be able to translate even the tiniest movements — within the micron range — into data. The smaller the minimum range of movement, the more complete the motion data will be. Extremely accurate systems will cost much more, but amateurs can use cameras within the high micron or millimeter range to save money.

When someone purchases a motion tracking camera, he or she will typically get software that is responsible for translating the movements captured by the cameras into data. Each program has a limit on the number of cameras that it can control simultaneously. A higher camera threshold means a better field of view, so the software can capture motion at many angles.

How Does a Motion Sensor Work?

The way in which a motion sensor works typically depends on the type of sensor being used, which often depends on the device that uses the sensor. One of the most common types of sensor technology is an active sensor that sends out bursts of energy, which bounces back in a way similar to sonar. There are also passive sensors that do not send out any type of signal, but instead receive energy from their surroundings to detect motion. Some systems can also use a combination of both active and passive technology to create a motion sensor that emits and receives an energy signal.

A motion sensor is an electronic device — often part of a larger system, such as a light or camera — that detects motion to activate the system. There are two basic types of motion sensors: active sensors and passive sensors. Active sensors emit a signal, typically an ultrasonic burst of sound waves, similar to a sonar system, which is reflected by the surroundings; this reflected signal is received by the sensor. When something moves within the area of an active motion sensor, the change in signal that is reflected to the sensor activates the system. This type of sensor is often used for indoor security and automatic garage door openers.


Passive sensors are a type of motion sensor that do not emit a signal, but instead detect infrared radiation around the sensor. When a person or animal moves through the area, heat from the movement is detected by the sensor, which then activates the system to which it is connected. This type of motion sensor is often used for motion-activated lights or cameras in a security system. Passive sensors are typically set to detect only sudden or extreme changes in thermal radiation, which prevents such systems from activating due to changes in surrounding temperature caused by the sun rising or pavement cooling at night.

A motion sensor can also utilize a combination of passive and active technology. This type of system is often used in stores to trigger a sound when someone enters the business. The motion sensor usually consists of two parts: one that emits a laser or similar energy signal, and a second piece that receives the signal. When someone passes through the system, the signal is interrupted and the receiving piece activates a response such as a bell. This type of system is not usually used for security purposes, since the energy beam could be avoided quite easily to keep from activating the system.

What Is OpenCV Tracking?

Open Source Computer Vision Library is the full name for OpenCV, a programming functions library and open source toolkit for cross-platform use in real-time computer vision image processing and OpenCV tracking. Developed near the turn of the 21st century, it was initially purposed for three dimensional (3-D) display walls and ray tracing. Making use of creative coding, OpenCV can offer a framework to developers of performance-optimized vision-based code in a C or C++ interface initially, though available in several languages, and is adaptable for remote usage on hand-held devices. It is capable of video file real-time capture, basic video configurations, object detection, and motion and color tracking, among other functions. OpenCV is capable of camera calibrations as it can find and track camera calibrations and set stereo correspondence on video cameras.

The CalcGlobalOrientation function for OpenCV tracking calculates motion orientation of a specified region in conjunction with a second CalcMotionGradient command, and creates a motion history and timestamp to track motion direction, returning results in degrees and recording subsequent shifts. The final result would be a sum of the original orientation and the angles of shift. Reading and writing of image files and forcing of them to a three-channel color image, files can be modified, directly and indirectly accessed, and converted to grayscale images or color byte-images.


The optical flow of images can be directed by means of block matching tracking, and every pixel calculated and instructed in flow. Allocation and releasing of images for one-channel byte images or three-channel float images to set a region of interest or clone an image are possible. OpenCV allows the capture of frame images from a video sequence from a file from several cameras simultaneously by grabbing one image from each and then retrieving from them all, to create and edit new video flows.

Facial OpenCV tracking is done by means of its Camshift functions. This function implements an object tracking algorithm, finds the object center, creates a color histogram, calculates facial probability, then shifts location of the face’s rectangle in each video frame and makes adjustments by calculating size and angle. It concentrates the brightest pixels over the centered face and uses scale for adapting to smaller faces in subsequent frames if the image is retreating.

OpenCV tracking abilities are used in many applications. From facial recognition to gesture recognition, mobile robotics, human-computer interaction programs and stereopsis, which creates stereo vision depth perception by means of using two cameras, making use of object, color, and motion tracking. OpenCV also has statistical machine learning libraries containing decision tree learning modules, expectation-maximization tracking algorithms, gradient boosting trees, and artificial neural networks functioning modules.

What Is Motion Tracking?

Motion tracking is a technique that can be used for a number of different purposes, each of which may call for a varying degree of complexity. The basic idea behind motion tracking is that video frames can be analyzed in order to follow the position of an object through time. This can be useful for detecting the presence of any motion, such as in a surveillance system, or for the complex motion capture used in video editing. Motion tracking can also be used as an alternative to radar to follow distant objects, such as missiles, satellites, and space debris, while also providing a high resolution image.

The simplest form of motion tracking is typically used in surveillance systems. Rather than tracking the position of an object over time, these systems generally use some form of technology to sense the presence of motion to activate a video camera, recorder, or alarm. Infrared light or lasers are often used to sense motion in the form of a tripwire system, though video can also be analyzed for movement in order to trigger a recording or sound an alarm.


More complex types of motion tracking are designed to identify an object and follow it through consecutive video frames. In order to accomplish this, some type of computing device typically uses an algorithm to analyze each frame. An algorithm such as blob tracking can be useful for following human movement or any other object that can present a dynamically changing profile. Contour tracking is another type of algorithm that typically looks for and examines the outline of an object. More processor-intensive methods, such as kalman or particle filters, can be useful for following complex interactions, such as the tracked object moving behind an obstruction.

One common use of motion tracking is in video editing, where it can be used to capture the movements of a person or other object. These movements may then be mapped to a computer generated image, as is commonly seen in movies and television shows. This same type of technology has also become common in video games, where the tracking system analyzes the movements of a player's body or a control device to manipulate objects or characters on screen.

Motion tracking can also be useful in following objects in real time. The technology can be used to track objects such as airplanes, missiles, and space debris. One main advantage of this technique is that it can provide high resolution video of whatever object is being tracked, but it does require sufficient light to operate, unlike radar.