> 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/manual-markers-measurement-points.md).

# Manual Markers / Measurement Points

Manual Marker workflows use measured 3D points as calibration references.

This is useful when **Calibration Screens** cannot be used, for example in large environments such as stadiums, arenas, venues, stages, or architectural spaces.

{% hint style="info" %}
In the calibration tools, this workflow is referred to as **Manual Markers**.\
The actual objects created in the Project Tree are called **Measurement Points**.
{% endhint %}

## What Measurement Points Are

A **Measurement Point** represents one known 3D point in the project.

Each Measurement Point stores a position that can be used by Manual Marker workflows during calibration. The point is later referenced manually in captured camera images.

The calibration tool uses the relationship between:

* the known 3D position of the Measurement Point
* the matching 2D pixel position in the captured camera image

to calculate alignment, repositioning, or static camera calibration results.

***

## When to Use Manual Markers

Use Manual Markers when you cannot display or place Calibration Images on a known reference surface.

Typical use cases include:

* stadium AR workflows
* arena or venue calibration
* camera alignment using field markings
* stage or set calibration using measured reference points
* architectural alignment using measured building points
* repositioning an already calibrated camera setup using known points

Manual Markers are especially useful when the real-world environment already contains points or lines that can be measured accurately and are clearly visible in the camera image.

***

## Creating Measurement Points

Measurement Points are created as normal objects in the **Project Tree**.

Each Measurement Point is an individual object. For larger setups, it is recommended to organize Measurement Points inside **Folders**.

A Folder can be used as a parent object for multiple Measurement Points. Moving the Folder in 3D space also moves all child Measurement Points relative to that Folder.

This can be useful for:

* keeping the Project Tree organized
* grouping points by area
* using a local reference origin
* moving a complete point layout together

{% hint style="info" %}
For repeated point layouts, you can create one Measurement Point as a child of a Folder and use **Right-click → Arrange / Align** on the Folder to generate grids, lines, or other repeated point arrangements.
{% endhint %}

***

## Measurement Point Properties

A Measurement Point contains several properties for organization and visualization.

The most important property for calibration is the **position**.

Other properties, such as name, color, display style, and display size, are only used for visualization in the 3D viewport.

Typical display options include:

* **Marker Cone**
* **Line**
* **Sphere**

These options do not affect the calibration result. They are only used to make the points easier to identify, organize, and visually check in the viewport.

{% hint style="warning" %}
Only the measured 3D position of the Measurement Point is relevant for calibration. Display color, shape, and size do not change the calibration result.
{% endhint %}

***

## Entering Accurate Point Positions

Measurement Points can be positioned in the 3D viewport or by entering their coordinates in the Inspector.

For calibration workflows, measured coordinates should be entered as accurately as possible.

In professional environments, especially in large arenas, stadiums, or venues, it is recommended to measure reference points using accurate surveying equipment, such as a total station.

{% hint style="info" %}
A smaller number of accurately measured points is usually better than many points with uncertain or inaccurate coordinates.
{% endhint %}

***

## Using Measurement Points in Captures

Manual Marker workflows use captured camera images inside the Calibrator.

The calibration tool creates captures in the same way as other calibration workflows. These captures can be opened and inspected in the **Manual Marker Editor**.

Inside the Manual Marker Editor, Measurement Points are assigned manually to their matching pixel positions in the captured image.

The basic workflow is:

1. Open the calibration tool that uses Manual Markers.
2. Create the required captures.
3. Open the **Manual Marker Editor**.
4. Select a captured image.
5. Find a visible real-world point in the image.
6. Right-click the matching pixel position.
7. Select the corresponding Measurement Point from the list.
8. Repeat this for all visible Measurement Points in the capture.
9. Repeat the process for each capture used by the workflow.

This creates a 2D-to-3D reference between the captured camera image and the measured point in the project.

{% hint style="warning" %}
Place each Measurement Point reference as accurately as possible on the matching pixel in the captured image. Incorrect point placement directly affects the calibration result.
{% endhint %}

***

## Single Capture and Multi Capture Workflows

The number of captures depends on the selected calibration workflow.

For **Simple Static Calibration with Marker**, usually only one capture is used because the camera is static.

For **Alignment with Markers**, multiple captures are used. Each capture represents a different camera view or tracking position.

Measurement Points must be referenced separately for each capture, because different points may be visible from different camera angles.

For example:

* Capture 1 may contain points `A, B, C, D, E, F`
* Capture 2 may contain points `E, F, G, H, I, K`
* Capture 3 may contain points `H, I, J, K, L, M`

This is expected. Not every Measurement Point needs to be visible in every capture. Each capture only needs the points that are clearly visible and can be accurately referenced in that image.

***

## Requirements and Best Practices

The quality of Manual Marker workflows depends heavily on the quality of the measured points and the accuracy of the manual pixel placement.

Good Measurement Points should be:

* accurately measured
* clearly visible in the camera image
* easy to identify without ambiguity
* spread across the visible image area when possible
* stable and not moving
* based on real physical features that can be found again later

For most Manual Marker calibration workflows, try to use at least `6–9` clearly visible Measurement Points per capture when possible.

More points can improve the result, but only if they are measured accurately.

***

## Point Distribution

Measurement Points should be distributed across the image whenever possible.

Good distribution helps the calibration tool understand the relationship between the camera image and the measured 3D environment.

Ideally, points should:

* be spread across the image
* cover different directions or axes in the scene
* not all be concentrated in one small area
* include different depths or heights when available

Points can lie on a line, for example when using field lines in a stadium. However, each capture should still include points that provide enough spatial variation whenever possible.

Different depths or heights can improve the calibration result, but they are not always available. In stadium workflows, many usable points may be located on the field surface only.

***

## Point Visibility

Only use Measurement Points that can be clearly identified in the captured image.

In the Manual Marker Editor, the user places a reference point on the image to define the 2D pixel position that corresponds to the selected 3D Measurement Point.

If a point is hidden, blurry, ambiguous, or difficult to identify, it is better to leave it out instead of guessing.

{% hint style="warning" %}
Do not use uncertain points. A wrong point reference can reduce the calibration quality more than a missing point.
{% endhint %}

***

## Typical Examples

Measurement Points can be created from any real-world point that is clearly identifiable and accurately measurable.

Good examples include:

* football field corners
* field lines
* penalty box corners
* goal lines
* center lines
* stage edges
* building corners
* architectural reference points
* measured floor markings
* other clearly identifiable and accurately measured points

For large environments such as stadiums, arenas, or venues, a professional measurement method is recommended. A total station can be used to measure accurate 3D coordinates for the reference points.

{% hint style="info" %}
The best Measurement Points are not defined by what they are, but by how clearly they can be identified in the camera image and how accurately their 3D position can be measured.
{% endhint %}

***

## Lens Profile Requirement

Most Manual Marker workflows require an existing **Lens Profile**.

The Lens Profile should usually be created before using Manual Markers, for example with a Calibration Screen workflow.

The main exception is **Simple Static Calibration with Marker**, which can be used without an existing Lens Profile because the result is written directly to the Camera Object.

***

## Validation After Calibration

Measurement Points can also be used to visually validate the calibration result.

After calibration, open the camera **Distortion Viewer** to compare the live camera image with the 3D viewport overlay.

The Distortion Viewer creates a technical AR-style composite of:

* the real camera image
* the calibrated camera view
* visible 3D objects from the viewport, including Measurement Points

This makes it possible to check whether the Measurement Points line up with their real-world positions in the camera image.

If the overlay does not match the image, check:

* whether the Measurement Point coordinates are correct
* whether the correct points were selected in the Manual Marker Editor
* whether the pixel positions were placed accurately
* whether the Lens Profile is valid
* whether the Tracking Data or Camera Object is correct for the selected workflow

***

## Tools That Use Manual Markers

Manual Markers are used by the following calibration and repositioning tools:

| Tool                                      | Main Purpose                                                                               |
| ----------------------------------------- | ------------------------------------------------------------------------------------------ |
| **Alignment with Markers**                | Creates or updates an Alignment Profile using Measurement Points and Tracking Data.        |
| **Simple Static Calibration with Marker** | Calibrates a static Camera Object using Measurement Points.                                |
| **Reposition from Marker**                | Repositions an existing calibrated camera setup or parent object using Measurement Points. |

The detailed steps for each tool are explained in the individual workflow pages.

***

## Before Starting Checklist

Before using Manual Markers, check the following:

* Measurement Points have been created in the Project Tree.
* Points are organized in Folders if the setup contains many points.
* Point coordinates have been measured accurately.
* Points are clearly visible in the camera image.
* Ambiguous or uncertain points are not used.
* A valid Lens Profile exists if required by the selected workflow.
* The correct calibration tool has been selected.
* Captures have enough visible Measurement Points for the selected workflow.
* Measurement Points are referenced accurately in the Manual Marker Editor.