---
title: "Step 1 - Load a Theia C3D file"
canonical: "https://help.vicon.com/space/ProCalc16/12649267/Step%201%20-%20Load%20a%20Theia%20C3D%20file"
format: markdown
---
Before you begin, ensure you have unzipped the ProCalc Tutorials data as described in [About the data in this tutorial](https://vicon-help.atlassian.net/wiki/spaces/ProCalc16/pages/12649218/Vicon+ProCalc+Theia+Tutorial#AboutData).


For this tutorial, the example trial data (*Walk01.c3d*) was generated by using Nexus pipelines that merged the rotation data from Theia with existing Vicon data (only force plates in this instance). You can also use a C3D that was directly processed in Theia.

For information on how a Theia3D file is added to a Nexus session folder and how to merge Theia3D data with a Nexus trial, see [Run Theia processing on video files](https://vicon-help.atlassian.net/wiki/spaces/Nexus216/pages/11600656) in the *Vicon Nexus User Guide*.

When you open the file in ProCalc, skeletal data from Theia3D is visualized as a skeleton in the ProCalc 3D workspace:

![image](media://538d3f8e-ac5d-4abb-949e-f8fdf6be29dc)

Each Theia segment is visualized as a bone. Each bone has an axis system that shows the XYZ axes of the bone's local coordinate system, with the axis system placed at the segment's point of origin. 

> Macro (scroll-pagebreak)

The axis system is displayed as follows:

- X-axis: red
- Y-axis: green
- Z-axis: blue

Each segment that is read from the C3D file is interpreted as a ProCalc segment – that is, an entity with a position (the segment's origin) and an orientation in 3D space.

ProCalc now lets you define your own calculations based on the segments.