The following paragraphs describe the basic parameters that must exist in almost every C3D file that contains 3D and/or analog data. You will find that most common applications that read C3D files will expect to find these parameters containing sensible values whenever a C3D file is opened. If you are attempting to implement C3D file compatibility in an application then this chapter describes the minimum parameter set that is required to fully describe the data. All parameter data values are stored in a common format and can be examined and modified by appropriate applications.
The term parameter in a C3D file refers to certain quantities that may need to be communicated to programs that access the C3D file in order to process the data correctly. Additionally, some useful descriptive information is stored in parameter format for convenient access and reference by the user.
A C3D file can contain many different parameters – some of these are essential and are found in every C3D file, while other parameters will only be seen in C3D files from specific manufacturers or are parameters generated by post-processing of the data. This situation is complicated by the inherently general nature of the C3D file. Most C3D files contain 3D point data and analog data related to the 3D data – however, it is possible to generate valid C3D files that contain only 3D data or files that contain only analog data. These files must include some parameters that serve simply to indicate that the file does not have a particular data type.
Not all parameters are intended to be editable – the parameter record contains a locking mechanism that may be set to indicate that a parameter should not be modified by the user after it has been set by a program. Such parameters are either assigned values by programs (and inappropriate values could cause other programs using that data to malfunction), or else contain data of an informational nature (e.g., the time at which a calibration was performed), which should not be changed.
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