The C3D specification expects all physical measurements to be one of two types, physical location information (for example, 3D locations or coordinates) referenced to a common origin, and numeric data (digital analog information).
The 3D Point format stores 3D location data as three X, Y, and Z locations, together with information about the sample – the accuracy (the average error or residual) of the 3D Point coordinate and optionally the camera contribution (recording the sensors or cameras used to generate the data). Each recorded set of coordinates is referenced to a common origin within the data collection volume, making the analysis and processing of 3D data collected in different environments simple.
Each sample of numeric data stored with the 3D Point data can contain digitized analog information from sources such as Electromyography, Accelerometers, Goniometers, Load Cells, Inertial Measurement Units, and Force Plates etc. These samples can be stored in synchronization with the 3D coordinate samples in the C3D file, so that it is easy to determine the numeric data values related to any 3D Point sample within the file.