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Saturday, April 25, 2009

Computer

A computer is a programmable machine that receives input, stores and manipulates data, and provides output in a useful format.
While a computer can, in theory, be made out of almost anything (see misconceptions section), and mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs). Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Simple computers are small enough to fit into mobile devices, and can be powered by a small battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous.

History of Computing
The first use of the word "computer" was recorded in 1613, referring to a person who carried out calculations, or computations, and the word continued to be used in that sense until the middle of the 20th century. From the end of the 19th century onwards though, the word began to take on its more familiar meaning, describing a machine that carries out computations.

Limited-function ancient computers
The history of the modern computer begins with two separate technologies—automated calculation and programmability—but no single device can be identified as the earliest computer, partly because of the inconsistent application of that term. Examples of early mechanical calculating devices include the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism, an ancient astronomical computer built by the Greeks around 80 BC. The Greek mathematician Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when. This is the essence of programmability.
The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered to be the earliest programmable analog computer. It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gateway causing automatic doors to open every hour, and five robotic musicians who played music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed to compensate for the changing lengths of day and night throughout the year.
The Renaissance saw a re-invigoration of European mathematics and engineering. Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers, but none fit the modern definition of a computer, because they could not be programmed.

First general-purpose computers
In 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing a series of punched paper cards as a template which allowed his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.
It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer, his analytical engine. Limited finances and Babbage's inability to resist tinkering with the design meant that the device was never completed.
In the late 1880s, Herman Hollerith invented the recording of data on a machine readable medium. Prior uses of machine readable media, above, had been for control, not data. "After some initial trials with paper tape, he settled on punched cards ..." To process these punched cards he invented the tabulator, and the keypunch machines. These three inventions were the foundation of the modern information processing industry. Large-scale automated data processing of punched cards was performed for the 1890 United States Census by Hollerith's company, which later became the core of IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.
During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.
Alan Turing is widely regarded to be the father of modern computer science. In 1936 Turing provided an influential formalisation of the concept of the algorithm and computation with the Turing machine, providing a blueprint for the electronic digital computer. Of his role in the creation of the modern computer, Time magazine in naming Turing one of the 100 most influential people of the 20th century, states: "The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine".

The Atanasoff–Berry Computer (ABC) was among the first fully electronic digital binary computing devices. Conceived in 1937 by Iowa State College physics professor John Atanasoff, and built with the assistance of graduate student Clifford Berry, the machine was not programmable in the modern sense, being designed only to solve systems of linear equations. The computer did employ parallel computation. A 1973 court ruling in a patent dispute found that the patent for the 1946 ENIAC computer derived from the Atanasoff–Berry Computer.
The inventor of the program-controlled computer was Konrad Zuse, who built the first working computer in 1941 and later in 1955 the first computer based on magnetic storage.
George Stibitz is internationally recognized as a father of the modern digital computer. While working at Bell Labs in November 1937, Stibitz invented and built a relay-based calculator he dubbed the "Model K" (for "kitchen table", on which he had assembled it), which was the first to use binary circuits to perform an arithmetic operation. Later models added greater sophistication including complex arithmetic and programmability.
A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult.Shannon 1940 Notable achievements include.
Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
The non-programmable Atanasoff–Berry Computer (commenced in 1937, completed in 1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory. The use of regenerative memory allowed it to be much more compact than its peers (being approximately the size of a large desk or workbench), since intermediate results could be stored and then fed back into the same set of computation elements.
The secret British Colossus computers (1943), which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
The U.S. Army's Ballistic Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.
Stored-program architecture
Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first working prototype to be demonstrated was the Manchester Small-Scale Experimental Machine (SSEM or "Baby") in 1948. The Electronic Delay Storage Automatic Calculator (EDSAC), completed a year after the SSEM at Cambridge University, was the first practical, non-experimental implementation of the stored program design and was put to use immediately for research work at the university. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.
Beginning in the 1950s, Soviet scientists Sergei Sobolev and Nikolay Brusentsov conducted research on ternary computers, devices that operated on a base three numbering system of −1, 0, and 1 rather than the conventional binary numbering system upon which most computers are based. They designed the Setun, a functional ternary computer, at Moscow State University. The device was put into limited production in the Soviet Union, but supplanted by the more common binary architecture.

Semiconductors and microprocessors
Computers using vacuum tubes as their electronic elements were in use throughout the 1950s, but by the 1960s had been largely replaced by transistor-based machines, which were smaller, faster, cheaper to produce, required less power, and were more reliable. The first transistorised computer was demonstrated at the University of Manchester in 1953. In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the late 1970s, many products such as video recorders contained dedicated computers called microcontrollers, and they started to appear as a replacement to mechanical controls in domestic appliances such as washing machines. The 1980s witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.
Modern smartphones are fully programmable computers in their own right, and as of 2009 may well be the most common form of such computers in existence.

Friday, April 10, 2009

Maniac Mansion (Game)

Plot summary
It has been twenty years, to the day, since a mysterious purple meteor came hurtling out of the sky and made a large crater in the front lawn of a huge Victorian-era mansion belonging to the Edison family. Dr. Fred, his wife Nurse Edna, and their son Edward "Weird Ed" Edison were reclusive people who left the house very rarely, but the meteor's arrival brought about a strange change in Dr. Fred and the family were seen even less, and even their mansion has fallen into disrepair. Lately, patients from the local hospital have begun to disappear without trace.
Now, a local teenage cheerleader, Sandy Pantz, has been kidnapped. Dave Miller, her boyfriend, saw her being carried off to the Edison's mansion and has gathered a few of his college pals on a rescue mission to invade the mansion and save Sandy. The player could select the friends from a group of six, and the game would play somewhat differently depending on which friends were selected. The game was a parody of the horror B-movie genre, featuring a secret lab, disembodied tentacles, and an evil mastermind.

Gameplay
Maniac Mansion was notable for its multiple possible endings, depending on which characters the player used (and which ones survived) and what those characters did. For instance, you can send the adversary off into space, or have him arrested by the Meteor Police, or make him famous by having his autobiography published, or, in some versions, feed him to the mutant plant. The game also allows permadeath, which is unusual for Lucas games. If one character dies, replacement needs to be selected, and if all characters die you will get a game over.
The game featured some notorious red herrings, such as a chainsaw for which there was no fuel, despite many wishful rumours to the contrary. In one of the in-jokes that are a hallmark of the LucasArts adventure games, the second SCUMM game, Zak McKracken and the Alien Mindbenders, contains some fuel "for chainsaws only", but no chainsaw. Another red herring is the staircase in the library (with a sign reading "staircase out of order") that appears to be a puzzle, but in fact there is no way to fix it or cross it. During development, it had been planned to put a room there, but the room was left out due to a lack of disk space. One notable bug in Commodore 64 version of the game was at the Garage near the pool. If you didn't open the Garage door, you can select the top of the garage with the Walk-To option and the player's character would walk up the garage door like it was a staircase.

Playable characters
Maniac Mansion has a total of seven possible player characters. The player controls Dave, the main protagonist (unless he dies), and two other characters, chosen from six additional characters, each of whom has their own distinct skills and quirks:
Syd, an aspiring New Wave musician. He specializes in musical instruments.
Michael F. Stoppe, an amateur photographer, aspiring to be a professional photographer. He works for the college newspaper and is able to develop film.
Wendy, an aspiring novelist with writing and editing skills.
Bernard Bernoulli, a nerd suffering from cowardice (he runs away from Green Tentacle until another character makes friends with it). He has the most skills of any character in the game, as he can disassemble the radio in the den, fix the HAM radio, the torn wiring in the attic, and fix the telephone in the library. His presence in the game, although optional like the rest of the kids, is significant (and perhaps canonical) because he reappears in Maniac Mansion: Day of the Tentacle as the main playable character.
Razor, a female punk rocker. Her talents are identical to Syd's. She was based on Gary Winnick's girlfriend. Her band, Razor and the Scummettes, is referred to in Zak McKracken. She reappears as a member of "The Vultures" biker gang in the 1995 game Full Throttle.
Jeff Woodie, a "surfer dude", is the least talented character of the group after Dave, as his only ability is to repair the telephone, which Bernard can also do. However, the game is still completable with Jeff in a player's party.

The Edisons
The titular mansion is owned by Dr. Fred Edison and his bizarre family. Most of the Edisons pose a threat and will throw the player into the dungeon (or kill them, in some instances) if they are spotted. The exceptions are Weird Ed, who under certain circumstances can be convinced to side with the player, and the relatively harmless Green Tentacle.

Tuesday, April 7, 2009

King's Quest (Game)

King's Quest is an adventure game series created by the American personal computer game company Sierra Entertainment. It is widely considered as a classic series from the golden era of adventure games. Following the success of its first installment, the series was primarily responsible for building the reputation of Sierra. Roberta Williams, co-founder and former co-owner of Sierra, designed all of the King's Quest games.
The King's Quest series chronicles the saga of the royal family of the Kingdom of Daventry through their various trials and adventures. The story takes place over two generations and across many lands, including Daventry, Kolyma, Llewdor, Tamir, Serenia, Eldritch, Etheria and the Land of the Green Isles.

Games and media releases
Wizard and the Princess (1980)/Adventure in Serenia (1982)
King's Quest: Quest for the Crown (1984, 1990 - enhanced Sierra's Creative Interpreter remake)
King's Quest II: Romancing the Throne (1985)
King's Quest III: To Heir Is Human (1986)
King's Quest IV: The Perils of Rosella (1988)
King's Quest V: Absence Makes the Heart Go Yonder! (1990)
King's Quest VI: Heir Today, Gone Tomorrow (1992)
King's Questions, a King's Quest trivia game (1994)
King's Quest VII: The Princeless Bride (1994)
King's Quest: Mask of Eternity (1998)

King's Quest 9
King's Quest 9 was a game in development by Sierra during 2001-2002. It was cancelled before going into production. The game never made it past the prototype stage. Images of two renders of the playable character were leaked to the public.

Collections

King's Quest 15th Anniversary Collector's Edition (1994)
Contains 1 (AGI & SCI versions) through 6, The King's Questions, King Graham's Board Game Challenge. It also contains a french floppy version of KQ5, and the german floppy version of KQ6. It also contains Inside the Chest, Behind the Developer's Shield, A View from Inside the Mirror, Hold onto your Adventurer's Cap, and The Royal Scribe, programs which contain concept material, artwork, documents, magazine articles, etc.
It also contains assorted videos, including making of, interviews, anniversery material, promo videos for KQ7, etc. The Fun Has Just Begun, Sierra Technology History, 15 Years of Products, Roberta Williams's Inspiration Interview, Ken & Roberta Sierra Future Interview, Roberta Williams Designer Interview, the Making of KQ6, Intro Sequence, KQ6 Art Slideshow, KQ7 Promo, and two About KQ7 interviews.

King's Quest Collection (1995)
It contains 1 (AGI & SCI versions) through 6, King's Questions, Graham's Board Game Challenge. It contains all of the bonus material from the 15th Anniversery Collector's Edition, and added a playable demo of KQ7.

King's Quest Collection Series (1997)
Also known as King's Quest Collection 2; it contains 1 (AGI & SCI versions) through 7 (2.0 version), King's Questions, Graham's Board Game Challenge, Wizard and the Princess, Mixed-Up Mother Goose Deluxe, Laura Bow 1 & 2, Mystery House, Mission Asteroid, and Time Zone.
It contains most of the bonuses from the previous versions, including Developer's Shield, Royal Scribe, and Chest. It does not contain all of the videos from the previous versions. It contains making of and intro videos for KQ6, and the intro and ending videos for KQ7. It has an added sneak peek of KQ8: Mask of Eternity.

Roberta Williams Anthology (1997)
It contains KQ1 (AGI & SCI versions) through 7 (2.0 version), Wizard and the Princess. It also contains Laura Bow 1 & 2, Mixed-up Mother Goose (AGI & VGA versions), Mystery House, Mission Asteroid, Time Zone, Dark Crystal, and Chapter 1 Demo of Phantasmagoria.
It contains the Chest & Developer's Shield, as well as box covers, and KQ7 concept art. Videos contain some of the videos from the first collection (that were not included in the "Collection 2"), and more interviews from the development teams, and a different Mask of Eternity sneak preview.

King's Quest Collection (2006)
In September 2006 Vivendi Universal released King's Quest Collection, a compilation CD for Windows XP encompassing games I-VII. Rather than porting the games directly, however, this release uses the original versions running under the DOSBox emulator and a Windows frontend. As a result, it is also possible to run King's Quest I-VI on other platforms with a little tweaking and ports of DOSBox. King's Quest VII is the earlier 16 bit windows version, version 1.4. It lacks dos compatibility, the improved save and restore functions, and character speed control found in version 2.0. It contains the dragon tail death that was removed from version 2.0, "Father always said to let sleeping dragons lie". It runs natively on Windows 32bit versions but is incompatible with 64bit windows.
Missing in the collection are the original AGI version of King's Quest 1, as well as the Windows CD version of King's Quest VI with high-resolution character art (some of the original Windows files were removed from this release), the 2.0 dos and windows versions of KQ VII, and King's Quest: Mask of Eternity. It also lacks any of the bonus material from previous collections.
This collection was released on Steam in July 2009.

King's Quest 1+2+3, 4+5+6, and 7+8 collections (2010)
Three collections released by Activison through GOG.com. The first consists of the classic AGI versions of King's Quest I-III[2] released 2010, and the later games King's Quest 4-5-6 on Vista. The final collection contains King's Quest 7 and 8 designed to work on Vista and Windows 7 32bit and 64bit.

Sunday, April 5, 2009

Motion Capture Methods

Motion tracking or motion capture started as a photogrammetric analysis tool in biomechanics research in the 1970s and 1980s, and expanded into education, training, sports and recently computer animation for television, cinema and video games as the technology matured. A performer wears markers near each joint to identify the motion by the positions or angles between the markers. Acoustic, inertial, LED, magnetic or reflective markers, or combinations of any of these, are tracked, optimally at least two times the frequency rate of the desired motion, to submillimeter positions.

Optical Systems
Optical systems utilize data captured from image sensors to triangulate the 3D position of a subject between one or more cameras calibrated to provide overlapping projections. Data acquisition is traditionally implemented using special markers attached to an actor; however, more recent systems are able to generate accurate data by tracking surface features identified dynamically for each particular subject. Tracking a large number of performers or expanding the capture area is accomplished by the addition of more cameras. These systems produce data with 3 degrees of freedom for each marker, and rotational information must be inferred from the relative orientation of three or more markers; for instance shoulder, elbow and wrist markers providing the angle of the elbow.

Passive markers
Passive optical system use markers coated with a retroreflective material to reflect light back that is generated near the cameras lens. The camera's threshold can be adjusted so only the bright reflective markers will be sampled, ignoring skin and fabric.
The centroid of the marker is estimated as a position within the 2 dimensional image that is captured. The grayscale value of each pixel can be used to provide sub-pixel accuracy by finding the centroid of the Gaussian.
An object with markers attached at known positions is used to calibrate the cameras and obtain their positions and the lens distortion of each camera is measured. Providing two calibrated cameras see a marker, a 3 dimensional fix can be obtained. Typically a system will consist of around 6 to 24 cameras. Systems of over three hundred cameras exist to try to reduce marker swap. Extra cameras are required for full coverage around the capture subject and multiple subjects.
Vendors have constraint software to reduce problems from marker swapping since all markers appear identical. Unlike active marker systems and magnetic systems, passive systems do not require the user to wear wires or electronic equipment. Instead, hundreds of rubber balls are attached with reflective tape, which needs to be replaced periodically. The markers are usually attached directly to the skin (as in biomechanics), or they are velcroed to a performer wearing a full body spandex/lycra suit designed specifically for motion capture. This type of system can capture large numbers of markers at frame rates as high as 2000fps. The frame rate for a given system is often balanced between resolution and speed: a 4-megapixel system normally runs at 370 hertz, but can reduce the resolution to .3 megapixels and then run at 2000 hertz. Typical systems are $100,000 for 4-megapixel 360-hertz systems, and $50,000 for .3-megapixel 120-hertz systems.

Active marker
Active optical systems triangulate positions by illuminating one LED at a time very quickly or multiple LEDs with software to identify them by their relative positions, somewhat akin to celestial navigation. Rather than reflecting light back that is generated externally, the markers themselves are powered to emit their own light. Since Inverse Square law provides 1/4 the power at 2 times the distance, this can increase the distances and volume for capture.
The TV series ("Stargate SG1") episode was produced using an active optical system for the VFX. The actor had to walk around props that would make motion capture difficult for other non-active optical systems.
ILM used active Markers in Van Helsing to allow capture of the Harpies on very large sets. The power to each marker can be provided sequentially in phase with the capture system providing a unique identification of each marker for a given capture frame at a cost to the resultant frame rate. The ability to identify each marker in this manner is useful in realtime applications. The alternative method of identifying markers is to do it algorithmically requiring extra processing of the data.

Time modulated active marker
Active marker systems can further be refined by strobing one marker on at a time, or tracking multiple markers over time and modulating the amplitude or pulse width to provide marker ID. 12 megapixel spatial resolution modulated systems show more subtle movements than 4 megapixel optical systems by having both higher spatial and temporal resolution. Directors can see the actors performance in real time, and watch the results on the mocap driven CG character. The unique marker IDs reduce the turnaround, by eliminating marker swapping and providing much cleaner data than other technologies. LEDs with onboard processing and a radio synchronization allow motion capture outdoors in direct sunlight, while capturing at 480 frames per second due to a high speed electronic shutter. Computer processing of modulated IDs allows less hand cleanup or filtered results for lower operational costs. This higher accuracy and resolution requires more processing than passive technologies, but the additional processing is done at the camera to improve resolution via a subpixel or centroid processing, providing both high resolution and high speed. These motion capture systems are typically under $50,000 for an eight camera, 12 megapixel spatial resolution 480 hertz system with one actor.

Semi-passive imperceptible marker
One can reverse the traditional approach based on high speed cameras. Systems such as Prakash use inexpensive multi-LED high speed projectors. The specially built multi-LED IR projectors optically encode the space. Instead of retro-reflective or active light emitting diode (LED) markers, the system uses photosensitive marker tags to decode the optical signals. By attaching tags with photo sensors to scene points, the tags can compute not only their own locations of each point, but also their own orientation, incident illumination, and reflectance.
These tracking tags that work in natural lighting conditions and can be imperceptibly embedded in attire or other objects. The system supports an unlimited number of tags in a scene, with each tag uniquely identified to eliminate marker reacquisition issues. Since the system eliminates a high speed camera and the corresponding high-speed image stream, it requires significantly lower data bandwidth. The tags also provide incident illumination data which can be used to match scene lighting when inserting synthetic elements. The technique appears ideal for on-set motion capture or real-time broadcasting of virtual sets but has yet to be proven.

Markerless
Emerging techniques and research in computer vision are leading to the rapid development of the markerless approach to motion capture. Markerless systems such as those developed at Stanford, University of Maryland, MIT, and Max Planck Institute, do not require subjects to wear special equipment for tracking. Special computer algorithms are designed to allow the system to analyze multiple streams of optical input and identify human forms, breaking them down into constituent parts for tracking. Applications of this technology extend deeply into popular imagination about the future of computing technology. Several commercial solutions for markerless motion capture have also been introduced. Products currently under development include Microsoft's Kinect system for PC and console systems.

Non-Optical Systems

Inertial systems
Inertial Motion Capture technology is based on miniature inertial sensors, biomechanical models and sensor fusion algorithms. The motion data of the inertial sensors (inertial guidance system) is often transmitted wirelessly to a computer, where the motion is recorded or viewed. Most inertial systems use gyroscopes to measure rotational rates. These rotations are translated to a skeleton in the software. Much like optical markers, the more gyros the more natural the data. No external cameras, emitters or markers are needed for relative motions. Inertial mocap systems capture the full six degrees of freedom body motion of a human in real-time. Benefits of using Inertial systems include: no solving, portability, and large capture areas. Disadvantages include lower positional accuracy and positional drift which can compound over time.
These systems are similar to the Wii controllers but are more sensitive and have greater resolution and update rates. They can accurately measure the direction to the ground to within a degree. The popularity of inertial systems is rising amongst independent game developers, mainly because of the quick and easy set up resulting in a fast pipeline. A range of suits are now available from various manufacturers and base prices range from $25,000 to $80,000 USD.

Mechanical motion
Mechanical motion capture systems directly track body joint angles and are often referred to as exo-skeleton motion capture systems, due to the way the sensors are attached to the body. Performers attaches the skeletal-like structure to their body and as they move so do the articulated mechanical parts, measuring the performer’s relative motion. Mechanical motion capture systems are real-time, relatively low-cost, free-of-occlusion, and wireless (untethered) systems that have unlimited capture volume. Typically, they are rigid structures of jointed, straight metal or plastic rods linked together with potentiometers that articulate at the joints of the body. These suits tend to be in the $25,000 to $75,000 range plus an external absolute positioning system.

Magnetic systems
Magnetic systems calculate position and orientation by the relative magnetic flux of three orthogonal coils on both the transmitter and each receiver. The relative intensity of the voltage or current of the three coils allows these systems to calculate both range and orientation by meticulously mapping the tracking volume. The sensor output is 6DOF, which provides useful results obtained with two-thirds the number of markers required in optical systems; one on upper arm and one on lower arm for elbow position and angle. The markers are not occluded by nonmetallic objects but are susceptible to magnetic and electrical interference from metal objects in the environment, like rebar (steel reinforcing bars in concrete) or wiring, which affect the magnetic field, and electrical sources such as monitors, lights, cables and computers. The sensor response is nonlinear, especially toward edges of the capture area. The wiring from the sensors tends to preclude extreme performance movements. The capture volumes for magnetic systems are dramatically smaller than they are for optical systems. With the magnetic systems, there is a distinction between “AC” and “DC” systems: one uses square pulses, the other uses sine wave pulse.

Thursday, April 2, 2009

Motion Capture

Motion capture, motion tracking, or mocap are terms used to describe the process of recording movement and translating that movement on to a digital model. It is used in military, entertainment, sports, and medical applications, and for validation of computer vision and robotics. In filmmaking it refers to recording actions of human actors, and using that information to animate digital character models in 2D or 3D computer animation. When it includes face and fingers or captures subtle expressions, it is often referred to as performance capture.
In motion capture sessions, movements of one or more actors are sampled many times per second, although with most techniques (recent developments from Weta use images for 2D motion capture and project into 3D), motion capture records only the movements of the actor, not his/her visual appearance. This animation data is mapped to a 3D model so that the model performs the same actions as the actor. This is comparable to the older technique of rotoscope, such as the 1978 The Lord of the Rings animated film where the visual appearance of the motion of an actor was filmed, then the film used as a guide for the frame-by-frame motion of a hand-drawn animated character.
Camera movements can also be motion captured so that a virtual camera in the scene will pan, tilt, or dolly around the stage driven by a camera operator while the actor is performing, and the motion capture system can capture the camera and props as well as the actor's performance. This allows the computer-generated characters, images and sets to have the same perspective as the video images from the camera. A computer processes the data and displays the movements of the actor, providing the desired camera positions in terms of objects in the set. Retroactively obtaining camera movement data from the captured footage is known as match moving or camera tracking.

Advantages
Motion capture offers several advantages over traditional computer animation of a 3D model:
More rapid, even real time results can be obtained. In entertainment applications this can reduce the costs of keyframe-based animation. For example: Hand Over
The amount of work does not vary with the complexity or length of the performance to the same degree as when using traditional techniques. This allows many tests to be done with different styles or deliveries.
Complex movement and realistic physical interactions such as secondary motions, weight and exchange of forces can be easily recreated in a physically accurate manner.
The amount of animation data that can be produced within a given time is extremely large when compared to traditional animation techniques. This contributes to both cost effectiveness and meeting production deadlines.
Potential for free software and third party solutions reducing its costs.

Disadvantages
Specific hardware and special programs are required to obtain and process the data.
The cost of the software, equipment and personnel required can potentially be prohibitive for small productions.
The capture system may have specific requirements for the space it is operated in, depending on camera field of view or magnetic distortion.
When problems occur it is easier to reshoot the scene rather than trying to manipulate the data. Only a few systems allow real time viewing of the data to decide if the take needs to be redone.
The initial results are limited to what can be performed within the capture volume without extra editing of the data.
Movement that does not follow the laws of physics generally cannot be captured.
Traditional animation techniques, such as added emphasis on anticipation and follow through, secondary motion or manipulating the shape of the character, as with squash and stretch animation techniques, must be added later.
If the computer model has different proportions from the capture subject, artifacts may occur. For example, if a cartoon character has large, over-sized hands, these may intersect the character's body if the human performer is not careful with their physical motion.