# Relationship

Capturing relationships enables autonomous systems to navigate complex scenes (such as road environments) effectively, ensuring safety, efficiency, and a better user experience.

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> User can create relationship across sensors, if needed.
{% endhint %}

***

## Benefits

* **Collision Avoidance and Safety:** Understanding which object is leading and which is following helps autonomous vehicles maintain safe following distances and prevent rear-end collisions.
* **Accurate Behavior Prediction:** Identifying leading and following objects enables the system to predict their behaviors, such as when the leading vehicle might slow down or stop, allowing the following vehicle to adjust accordingly.
  * Knowing which object is leading and following helps plan evasive actions during emergencies, such as sudden braking or unexpected obstacles.

***

## Steps to use Relationship

1. It is important to create the relations in the recipe to invoke this feature on the tool. In the recipe section, user will [create the relation](/project-setup/create-recipe/4.-associations.md#create-relations).
2. The tool is launched and the expert will create the two objects which are in a relationship. Upon creating the second object, the Relationship tab is enabled.

***

### Use Case 1 : One-way Relations

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> Most (if not all) use cases fall under this category. Examples would be a cars atop a trailer, a rider sitting on a two wheeler, stroller being pushed by a pedestrian, trailer connected to the cabin of a truck etc.
{% endhint %}

#### A. Select the Subject to Create a Relation

Consider the following example&#x20;

**Relationship 1** Subject **->** Rider **;** Object **->** TwoWheeler

<figure><img src="/files/a5egkmY7evhvD3O1nTLf" alt=""><figcaption></figcaption></figure>

1. User is prompted to select a relation on the tool
2. Based on the relation, the selected annotation becomes the Subject (i.e. child) in the relationship and is displayed on the left side across the tool:
   * under the relationship tab
   * in the attribute list

<figure><img src="/files/UvMXgnrNDRAF3D4ywdX5" alt=""><figcaption></figcaption></figure>

3. As a visual cue, on the point cloud, the **subject** will always have the **small** **sphere** and the **object** will always have the **big** **sphere**.

<figure><img src="/files/MdvDSOLYGzTLG93tCCjc" alt=""><figcaption></figcaption></figure>

#### B. Select the Object to Create a Relation

In this use case, the above recipe was used,&#x20;

1. User is prompted to select a relation on the tool
2. Based on the relation, the selected annotation becomes the Object (i.e. parent) in the relationship and is displayed on the right side across the tool:
   * under the relationship tab
   * in the attribute list
3. As a visual cue, on the point cloud, the **subject** will always have the **small** **sphere** and the **object** will always have the **big** **sphere**.

***

### Use Case 2 : Class Has Multiple Relations

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line">  A common example would be various categories of vehicles can be towed by a tow-truck.
{% endhint %}

In this use case, the following recipe was used,&#x20;

**Relationship 1** Subject **->** Rider **;** Object **->** TwoWheeler

**Relationship 2** Subject **->** Rider **;** Object **->** Bicycle

<figure><img src="/files/7faOjFptxxyxkh739vQ5" alt=""><figcaption></figcaption></figure>

1. User is prompted to select a relation on the tool since the selected annotation can be in a relationship with 2 annotations. &#x20;

<figure><img src="/files/oErWmJStPwWFlWR6R71F" alt="" width="359"><figcaption></figcaption></figure>

2. In the above example, *Rider* (subject) can be in a relationship with either *TwoWheeler* or *Bicycle* (two objects). The tool prompt will appear with multiple relations.
3. However, in this example, had the user selected the object (either *TwoWheeler* or *Bicycle*), the user would not have had to choose,

<figure><img src="/files/qTtnmr7dyxYIrPddPx6j" alt="" width="355"><figcaption></figcaption></figure>

4. The relationship is displayed on the tool uniformly, where left is subject and right is object:
   * under the relationship tab
   * in the attribute list
5. As a visual cue, on the point cloud, the **subject** will always have the **small** **sphere** and the **object** will always have the **big** **sphere**.

***

### Use Case 3 : Cyclic Relations

#### A. A Class Category is both Subject and Object&#x20;

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> A common example is a pedestrian is holding hands with another pedestrian.
{% endhint %}

In this use case, the following recipe was used,&#x20;

**Relationship 1** Subject **->** PassengerCar **;** Object **->** PassengerCar

<figure><img src="/files/kdr8oDpPg5D0fTPcVPTy" alt=""><figcaption></figcaption></figure>

1. User is prompted to select a relation on the tool.  Since the subject and object are identical (i.e. *PassengerCar)*, the tool prompt for relation will appear with options,

<figure><img src="/files/9vUxmghKXhvA1Fgzw4m5" alt="" width="374"><figcaption></figcaption></figure>

2. The selected annotation can become the Subject (i.e. child) in the relationship or the Object (i.e. parent) depending on whether the relation (i.e. *isAttachedTo*) selected was from Outgoing or the Incoming.
   * Outgoing - Selected annotation becomes the object
   * Incoming - Selected annotation becomes the subject

<figure><img src="/files/MxIcIsP8tAEG8DottpFZ" alt="" width="374"><figcaption></figcaption></figure>

3. The relationship is displayed on the tool uniformly, where left is subject and right is object:
   * under the relationship tab
   * in the attribute list
4. As a visual cue, on the point cloud, the **subject** will always have the **small** **sphere** and the **object** will always have the **big** **sphere**.

#### B. A Class Category is an Object in one Relationship and Subject in Another

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> A common example is a bi-articulated bus, where the centre is both a subject and an object entity.
{% endhint %}

In this use case, the following recipe was used,&#x20;

**Relationship 1** Subject **->** Rider **;** Object **->** TwoWheeler

**Relationship 2** Subject **->** Rider **;** Object **->** Bicycle

<figure><img src="/files/Bj7JWofa3HBgv1Blq9aA" alt=""><figcaption></figcaption></figure>

1. User is prompted to select a relation on the tool.  Since the subject and object are identical (i.e. *PassengerCar)*, the tool prompt for relation will appear with options,

<figure><img src="/files/N1wYpVsP280kZ3l9qtrs" alt="" width="358"><figcaption></figcaption></figure>

2. The selected annotation can become the Subject (i.e. child) in the relationship or the Object (i.e. parent) depending on whether the relation (i.e. *isAttachedTo*) selected was from Outgoing or the Incoming.
   * Outgoing - Selected annotation becomes the object
   * Incoming - Selected annotation becomes the subject
3. The relationship is displayed on the tool uniformly, where left is subject and right is object:
   * under the relationship tab
   * in the attribute list
4. As a visual cue, on the point cloud, the **subject** will always have the **small** **sphere** and the **object** will always have the **big** **sphere**.

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> The expert can select either the object or the subject and proceed to creating the relation in all Use Cases.
{% endhint %}


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