> For the complete documentation index, see [llms.txt](https://docs.theiamarkerless.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.theiamarkerless.com/theia3d-documentation/getting-started/theia3d-basics.md). # Theia3D Basics ## Theia3D Basics Theia3D is a markerless motion capture solution that utilizes synchronized video data to produce accurate and reliable 3D pose estimates of humans visible within the video data. It leverages deep learning algorithms trained to identify humans and accurately predict the 2D positions of 124 keypoints on the human body, in every video frame of every camera. By fitting a scaled subject-specific inverse kinematic model to the keypoint predictions, the human’s pose is reconstructed in 3D and tracked throughout their movement. This data-driven approach results in a robust solution that is generalizable across environments and movements, allowing the accessible collection of high quality 3D motion capture data where it was previously impossible. Here, we describe the basic framework for collecting markerless motion capture data using Theia3D; for more detailed instructions, please refer to the appropriate section of this documentation and any accompanying videos. Please refer to this blog post about the [General Framework for Data Collections.](https://www.theiamarkerless.com/blog/general-framework-for-data-collections) {% embed url="" %} *** ## **Calibration** Calibration is a crucial step for any 3D motion capture solution, and is equally important for Theia3D markerless motion capture data. The recommended calibration method depends on your camera system, but the concept and result is the same across all: determine the intrinsic and extrinsic parameters for all cameras in your system. These parameters allow lens effects and the 3D position and orientation of each camera to be determined, which is the key to producing robust 3D reconstructions. The calibration methods supported by Theia3D include: * Chessboard calibration, using a large printed chessboard pattern to automatically obtain intrinsic and extrinsic camera parameters. * Third-party calibrations, such as wand calibrations implemented by third-party motion capture hardware suppliers. * Object calibration, using an object with known dimensions or with precisely measured key point positions to manually obtain extrinsic camera parameters. See [Data Collection](/theia3d-documentation/data-collection.md) for details on recording intrinsic and extrinsic calibrations, and [Calibration Menu](/theia3d-documentation/theia3d-dropdown-menus/calibration-menu.md) for details on processing calibration trials. *** ## **Movement Data Collection** Once you have calibrated your system (e.g. [recorded an extrinsic chessboard calibration](/theia3d-documentation/data-collection/recording-extrinsic-chessboard-calibrations.md) or performed a third-party wand calibration), the next step is recording your movement trials. Before recording your data, consider the following: * What is an appropriate frame rate to capture this movement smoothly? * What is an appropriate exposure (shutter speed) to capture this movement clearly (i.e. without motion blur)? * Is the participant clearly visible, well lit, and captured with the highest resolution possible? * What are the analysis goals for this data? How can the movement be recorded to most efficiently meet these goals, avoiding excess video capture? Theia3D produces robust 3D pose estimates across varying environments, for humans wearing typical body-fitting clothing, and is task-agnostic. Therefore, if the human(s) in your video are clearly visible and captured with appropriate resolution, frame rate, and exposure, Theia3D's algorithms can generally track their motion without issue. Record your movement data with relative freedom and ease, following the recommendations outlined in the [Data Collection Principles](/theia3d-documentation/data-collection/important-factors.md) section. {% hint style="info" %} **Note:** Multi-person tracking in Theia3D is designed for controlled environments where individuals can be consistently distinguished. Performance degrades in dense, high-contact activities (e.g., basketball, wrestling) with prolonged overlap. Ensure subjects remain visible and separable across cameras for the majority of the trial. {% endhint %} *** ## ‍**Data Processing** Having collected calibration data and movement trials, you have everything required to process your markerless motion capture data. The steps below outline a typical data processing workflow: {% stepper %} {% step %} ### Organize video data Theia3D and Theia3D Batch require video data to be organized in a specific fashion, as outlined in [Video Data](/theia3d-documentation/data-formats/video-data.md). Use the [Organize Videos](/theia3d-documentation/theia3d-dropdown-menus/tools-menu/organize-videos.md) tool to achieve this organization. {% endstep %} {% step %} ### Process chessboard calibration (if required) If an extrinsic chessboard calibration was recorded, use the [Chessboard Calibration](/theia3d-documentation/theia3d-dropdown-menus/calibration-menu/chessboard-calibration.md) tool to process the calibration and save a calibration TXT file. If a third-party wand calibration was completed, you should already have a calibration TXT or XCP file, and this step is not required. {% endstep %} {% step %} ### Assign calibration to trials For batch-processing, it is necessary for the calibration TXT (or XCP) file to be assigned to the corresponding movement trials. Use the [Assign Calibration Files](/theia3d-documentation/theia3d-dropdown-menus/tools-menu/assign-calibration-files.md) tool to associate the calibration file with the movement trials from the same session. {% endstep %} {% step %} ### Processing Option 1: Theia3D Theia3D can be used to analyze movement trials on an individual basis. This can be useful for closely reviewing a single trial for quality assurance prior to batch processing, or if you have a limited number of movement trials. When using Theia3D, follow the basic steps below to analyze a single trial: 1. [Load video data](/theia3d-documentation/theia3d-dropdown-menus/file-menu.md#load-video-data) 2. [Load calibration file](/theia3d-documentation/theia3d-dropdown-menus/file-menu.md#load-calibration-file) 3. [Adjust preferences](/theia3d-documentation/theia3d-dropdown-menus/settings-menu/settings-menu.md) 4. [Run analysis](/theia3d-documentation/theia3d-dropdown-menus/analyze-menu.md#run-analysis) {% endstep %} {% step %} ### Processing Option 2: Theia3D Batch {% hint style="info" %} **Note:** It is always recommended to verify the data quality and calibration assignment in Theia3D prior to batch processing in Theia3D Batch. {% endhint %} Theia3D Batch can be used to analyze multiple movement trials automatically, without user supervision or intervention. This can be useful for processing large quantities of trials. When using Theia3D Batch, follow the basic steps below to analyze a batch of trials: 1. [Set batch directory data path](https://docs.theiamarkerless.com/theia3d-documentation/getting-started/pages/a4ZueauM24294RSkagrS#id-2.-data-path) 2. [Select desired output formats](/theia3d-documentation/theia3d-batch/settings.md#output-format) 3. [Modify trial list](/theia3d-documentation/theia3d-batch/trials.md) 4. [Adjust preferences](/theia3d-documentation/theia3d-batch/preferences.md) 5. Run Batch {% endstep %} {% endstepper %} For more information on analyzing data, check out the following video: {% embed url="" %} --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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