C3D File

What are C3D files and how to open them

Are you having problems opening a C3D file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your C3D files.

What is a C3D file?

C3D files have multiple uses, and Chem3D Format is one of them. Read more about the other uses further down the page.

Chem3D Format

These C3D files contain molecular visualizations created in Chem3D, a software created for chemists. This software is divided into three sections. These sections are two-dimensional chemical drawings, three-dimensional molecular modeling, and chemical information management. You have access to pre-generated molecular structures that can be found in the comprehensive internal sub-structure library.

How to open C3D files

Important: Different programs may use files with the C3D file extension for different purposes, so unless you are sure which format your C3D file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different C3D openers which you will find listed below.

Last updated: August 25, 2026

All known file formats using extension .C3D

While Chem3D Format is a popular type of C3D-file, we know of 4 different uses of the .C3D file extension. Different software may use files with the same extension for different types of data.

Coordinate 3D File

Coordinate 3D File format stores data from a single motion capture or biomechanics trial in a compact binary file that includes 3D point trajectories, synchronized analog signals (such as force or EMG), and metadata that describe how the data were collected. It was first created as part of the AMASS photogrammetry software by Dr. Andrew Dainis at ADTech in the mid-1980s and has remained in use in research and clinical biomechanics since then.

The format keeps all the essential information - camera calibration, residuals (error metrics), sampling rates, analog channel definitions, sign-scale factors, subject or trial identifiers - inside the file's parameter section, so that any program can interpret the raw coordinate and analog data without relying on separate documentation. The data section holds sequential frames: each frame contains all 3D point coordinates (X, Y, Z), optionally error or "residual" values and camera masks, followed immediately by analog samples.

Technical structure begins with a fixed-size header of 512 bytes, which includes the second byte (default ASCII "P", 0x50) that indicates use of the "3D point plus synchronized analog" storage mode. Data values are stored as scaled 16-bit integers or 32-bit floating-point numbers, depending on how the file is constructed, with scale factors defined in the parameter section.

Coordinate 3D Format

Coordinate 3D files are binary data files used to store raw motion capture data designed for biomechanics, gait analysis, clinical research, and animation work. These files contain 3D marker trajectories together with synchronized analog sensor data (such as force plates, electromyography, accelerometers), all in one archival file. The format allows storage of both physical measurements and detailed parameters that document how those measurements were made and how they should be interpreted.

Files are produced by motion capture systems or analysis software that measure marker coordinates over multiple frames, and optionally sample analog signals in sync with those frames. Software reading them can reconstruct the full dataset: the 3D trajectories for each marker, analog waveforms, and metadata such as label names, point descriptions, measurement units, data rates, and scaling. This lets users process, visualize, filter, or analyze experiments without losing context or precision.

Internally, the file begins with a header block (first 512 bytes) that defines the structure of the data section, including how many frames exist, where the data section starts, and whether data are stored as integers or floating-point. A parameter section follows, which includes fields like POINT:LABELS (unique identifier strings for each 3D marker), POINT:DESCRIPTIONS (human-readable descriptions for those markers), POINT:UNITS (distance units), and analog equivalents of these parameters. The data section holds frame-by-frame marker positions together with residuals and camera-masks, and analog channel samples synchronized to those frames.

One internal identifier signature is that the second byte of the header is 0x50h (the ASCII character "P"), which indicates that the file uses the 3D Point data format. Common parameter names in the file include POINT:DATA_START, POINT:LABELS, POINT:DESCRIPTIONS, POINT:FRAMES, POINT:USED, SCALE, UNITS, and strings like "DESCRIPTIONS", "DATA_START", "FRAMES", "LABELS", "POINT", "USED".

Dynamix 3D Data Container

We know that one C3D format is Dynamix 3D Data Container. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of C3D files. Remember, different programs may use C3D files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about C3D file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.