The C3D (Coordinate 3D, pronounced see-three-dee) data file format is a component of a family of file formats originally developed for the AMASS photogrammetry software system. AMASS, which stores its output data in C3D files, was developed by Andrew Dainis, Ph.D. as a commercial product during 1986 - 1987 to replace the relatively inefficient and inaccurate biomechanics photogrammetry software available at the time. The first installation was in the Biomechanics Laboratory at the National Institutes of Health where it has been in use ever since. Located in the United States in Bethesda Maryland, the National Institutes of Health (NIH) is one of the world’s foremost medical research centers. As an agency of the US Department of Health and Human Services, the NIH is a leading center for health research.
The C3D format provides a convenient and efficient means for storing 3D coordinate and analog data, together with all associated parameters, for a single measurement trial. The C3D file format has been in widespread use since 1987 and conforms to a publicly available C3D file format specification. This public specification is the basis for the information in this document.
The basic design of the ADTech file format (of which C3D is a member) was originally driven by the desire to have a single file format that would communicate parameters and data between the various components of AMASS (calibration, tracking, marker identification, etc.) and also serve as the output of the final 3D trajectory and analog data. Some high priority objectives were:
· Flexible storage of different types of data within the file.
· Flexible storage of parameters and parameter types in a “parameter section” of the file.
· To allow parameter to have descriptive names, and actual text descriptions so that the file could be self-documenting.
· To provide users with a single utility which they can use to add, examine, and if necessary modify, any parameter within any file.
· The efficient and compact storage of all the necessary information within a single file.
The essential idea behind the C3D format is that all 3D coordinate and numeric data for any recorded measurement is stored in a single file, together with the various parameters that describe the data. Before this time it had been (and in many instances still remains) common for the various Motion Capture systems to store their recorded data in many different files, often using several unique formats. The traditional approach presented a number of problems:
· Each manufacturer expended a considerable effort simply to document and maintain the large number of unique file formats.
· Updates and changes to software applications required careful design to maintain data consistency due to the number of file formats supported.
· Users were required to understand many file formats together with their interaction and interdependence in order to get to the data that they had recorded.
· The comparison of identical measurements between different manufacturers is virtually impossible due to the differing data and parameter storage methods and assumptions.
· System updates often introduced file format changes that rendered older data unreadable to the newer applications.
The development of the C3D format effectively solved all of the above problems. A single, well documented, binary format simplified both software maintenance and documentation, users could access their data from a single file, and the use of a common format made it easy for researchers and clinicians to compare information recorded in labs with different Motion Capture systems for the first time. The standardized and flexible design of the C3D format meant that data was no longer obsolete each time a manufacturer released a new version of their software applications or by advances with new hardware developments.
It is the ability to store information about the data that sets the C3D format apart from every other biomechanics format. The C3D file usually stores the 3D and analog data together with a small number of common parameters that describe the 3D data. The user may then define, generate, and store any number of user or lab defined data items within the file.
The C3D format allows this to be done using a standard format so that anyone opening the C3D file can access the information. As a result, adding parameter information to a C3D file is very easy. Since the C3D format is not tied to any specific manufacturer, it can be freely adapted to store the information that the users require without making a commitment to any specific manufacturer.
More:
