# Brush

The brush tool lets annotators paint directly over areas of the 3D point cloud to segment points by class - ideal for irregular, organic, or free-form shapes.

<figure><img src="/files/AeBqagOpS91SDQLlgavY" alt=""><figcaption></figcaption></figure>

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## Use Case

* **Segmentation**: Paint over regions to label areas of interest more intuitively than rigid tools allow.
* **Freeform Annotation**: Annotate irregular shapes or areas that are difficult to capture with cuboids or polygones.
* **Efficiency**: Label large or complex surfaces - vegetation, terrain, organic forms - faster within 3D environments.

The 3D paintbrush is particularly useful for annotating non-rectangular objects like vegetation, terrain, or other organic forms in 3D data.

***

## Create Segment

{% stepper %}
{% step %}

#### Start

Click the **+** icon next to your desired class in the class list to activate the brush tool.

{% hint style="success" %} <img src="/files/mXHEiGg35kYjwl0I4r5p" alt="" data-size="line"> An "i" icon appears on the [header](https://docs.imerit.net/3d-multi-sensor-fusion/labeling/3d-multi-sensor-fusion-labeling-editor/drawing-tools/pages/d6c7999cfa76444854c6d3fd201a73c58c97a394#id-1.-header) to aid the user with the controls.
{% endhint %}
{% endstep %}

{% step %}

#### Position the Brush Sphere

Hover the mouse over the drawing area. A gray circle (the brush sphere) appears, sharing the same depth as the point cloud layer beneath it. Points inside the brush tint yellow - a preview of what will be segmented.
{% endstep %}

{% step %}

#### Resize the Brush Sphere

Hold <kbd>Ctrl</kbd> and scroll the mouse wheel to increase or decrease the sphere size.
{% endstep %}

{% step %}

#### Paint

Hold the left mouse button and drag over the points you want to label. Yellow-tinted points are converted to the class color immediately as you paint.
{% endstep %}

{% step %}

#### Save

Once all target points are segmented, right-click to save. The annotation details pop-up will appear to confirm class and instance details.
{% endstep %}
{% endstepper %}

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## Editing a Segment

<figure><img src="/files/NkoZtc5x3TjTMes8KHzw" alt=""><figcaption></figcaption></figure>

### Adding a Segment

To segment (add) points to an existing annotation:

1. Click **+** against any class, and hover over the points. Points inside the brush tint yellow (if not already segmented).
2. Left-click and drag to further segment points
3. Right-click to save the changes.

### Deleting a Segment

To un-segment (remove) points from an existing annotation:

1. Click **+** against any class, then hold <kbd>Alt</kbd> and hover over the annotation. Points inside the brush sphere tint red to indicate they will be removed.
2. While keeping <kbd>Alt</kbd> held, left-click and drag to un-segment the red-tinted points.
3. Right-click to save the changes.

***

## Keyboard shortcuts

| Action                         | Shortcut                       |
| ------------------------------ | ------------------------------ |
| Increase / decrease brush size | <kbd>Ctrl</kbd> + scroll wheel |
| Enter erase mode               | Hold <kbd>Alt</kbd>            |
| Save annotation                | Right-click                    |

***

## Persistent settings

The last used brush sphere size is retained when switching between drawables or returning after a browser refresh.

{% hint style="info" %}
Paintbrush size survives browser refresh and logout / login.
{% endhint %}


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