> For the complete documentation index, see [llms.txt](https://stage-precision.gitbook.io/grid/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stage-precision.gitbook.io/grid/camera-calibration/before-you-start/calibration-references.md).

# Calibration References

Calibration references are known visual or spatial references that Grid Studio uses during camera calibration.

A calibration can only be solved accurately when Grid Studio knows where specific points, patterns, or reference surfaces are located in the real world. These references create the connection between the live camera image and the virtual 3D scene.

Grid Studio supports two main types of calibration references:

* **Calibration Screens** using generated calibration images
* **Manual Markers** based on measured 3D points

***

## Terminology

To keep the workflow clear, the following terms are used throughout this documentation:

<table><thead><tr><th width="210">Term</th><th>Meaning</th></tr></thead><tbody><tr><td><strong>Calibration Screen</strong></td><td>The Grid Studio concept or object that represents a known physical reference surface used for calibration.</td></tr><tr><td><strong>Calibration Image</strong></td><td>The exported image generated by Grid Studio and displayed or placed on the physical reference surface.</td></tr><tr><td><strong>Calibration Pattern</strong></td><td>The visible pattern inside the calibration image that is detected by the calibration tools.</td></tr><tr><td><strong>Reference Surface</strong></td><td>The real physical surface, such as an LED wall, monitor, TV, printed board, or measured calibration target.</td></tr><tr><td><strong>Manual Marker</strong></td><td>The workflow/tool term for manually assigning known 3D points to captured image positions.</td></tr><tr><td><strong>Measurement Point</strong></td><td>The actual object in the Project Tree that stores the measured 3D position used by Manual Marker workflows.</td></tr></tbody></table>

***

## Calibration Screens

The standard screen-based workflow uses Calibration Screens.

A Calibration Screen represents a known physical reference surface in Grid Studio. Grid Studio can generate calibration images for these surfaces. The calibration image is then displayed or placed on the real reference surface and used by the calibration tools as a known visual reference.

Calibration Screens can be used with:

* LED walls
* monitors
* TVs
* printed boards
* other precisely measured flat calibration targets

The important requirement is that the physical size of the reference surface is known and matches the configuration in Grid Studio.

For digital screens, the calibration image must be displayed pixel-correctly. For printed boards, the physical print size must match the dimensions configured in Grid Studio.

Projection-based calibration images are not part of the standard Calibration Screen workflow, because the final projected size of the calibration pattern can be difficult to guarantee accurately unless it is measured and controlled separately.

{% content-ref url="/pages/cAxk1UkOnjgooTgZBVig" %}
[Calibration Screens](/grid/camera-calibration/before-you-start/calibration-references/calibration-screens.md)
{% endcontent-ref %}

***

## Manual Markers

Manual Marker workflows use **Measurement Points** as known 3D references.

Each Measurement Point represents a measured point in the real-world environment. During calibration, the user manually selects the matching pixel position for that point in the captured camera image.

Instead of displaying a generated calibration image, known 3D points are measured in the real world and created manually inside Grid Studio. Each Manual Marker represents one clearly identifiable real-world point with a known 3D position.

Manual Markers can be useful in large environments such as stadiums, arenas, stages, or architectural spaces where it is not practical to place printed boards, monitors, or LED walls for calibration.

Examples of Manual Marker points include:

* field corners
* field lines
* stage measurement points
* architectural points
* clearly identifiable physical reference points

Manual Markers are often used for alignment workflows, such as aligning a tracking system to a measured environment or repositioning an already calibrated camera system.

{% content-ref url="/pages/0bGDLXp2eYRsl8OdTAnf" %}
[Manual Markers / Measurement Points](/grid/camera-calibration/before-you-start/calibration-references/manual-markers-measurement-points.md)
{% endcontent-ref %}

***

## Choosing the Right Reference Type

Use **Calibration Screens** when you can display or place a generated calibration image on a known physical reference surface.

Use **Manual Markers** when you cannot use generated calibration images, but you have measured real-world points that can be clearly identified in the camera image.

| Situation                                                      | Recommended reference type |
| -------------------------------------------------------------- | -------------------------- |
| LED wall calibration                                           | Calibration Screens        |
| Monitor or TV calibration                                      | Calibration Screens        |
| Printed calibration board                                      | Calibration Screens        |
| Multi-screen LED setup                                         | Calibration Screens        |
| Stadium AR with known field points                             | Manual Markers             |
| Architectural or stage alignment with measured points          | Manual Markers             |
| Repositioning an existing calibrated setup using known points  | Manual Markers             |
| Repositioning an existing calibrated setup using known screens | Calibration Screens        |

***

## Important Requirements

All calibration references must be accurate and stable.

For Calibration Screens:

* The physical size of the reference surface must be known.
* The Screen object in Grid Studio must match the real-world dimensions.
* The calibration image must match the configured screen setup.
* Digital screens must display the calibration image pixel-correctly.
* Printed boards must be printed at the correct physical size.
* The reference surface should not move during calibration.

For Manual Markers:

* Each point must have accurate 3D coordinates.
* Each point must be clearly visible or identifiable in the camera image.
* The points should be distributed well across the calibration area.
* Poorly measured marker positions will directly reduce calibration quality.

***

## How References Are Used

Calibration references are used by different tools depending on the workflow.

Calibration Screens are commonly used by:

* Lens & Tracking Calibration
* Lens & Tracking Calibration (Rotation Only)
* Lens Calibration
* Tracking Alignment
* Axis-Pole Calibration
* Simple Static Calibration
* Reposition from Screen
* Screen Reposition Without Profile
* Screens Alignment

Manual Markers are commonly used by:

* Alignment with Markers
* Simple Static Calibration with Marker
* Reposition from Marker

The following sections explain how to create and configure Calibration Screens, Single Screen setups, Multi Screen setups, and Manual Markers.