# Create semantic tags

Learn how to define customized tags for semantic segmentation. These can additionally be added to [carla.CityObjectLabel](python_api.md#carla.CityObjectLabel) to filter the bounding boxes that [carla.World](python_api.md#carla.World) retrieves.  

*   [__Create a new semantic tag__](#create-a-new-semantic-tag)  
	*   [1. Create the tag ID](#1-create-the-tag-id)  
	*   [2. Create the UE folder for assets](#2-create-the-ue-folder-for-assets)  
	*   [3. Create two-way correspondence between UE and the code tag](#3-create-two-way-correspondence-between-ue-and-the-code-tag)  
	*   [4. Define a color code](#4-define-a-color-code)  
	*   [5. Add the tagged elements](#5-add-the-tagged-elements)  
*   [__Add a tag to carla.CityObjectLabel__](#add-a-tag-to-carlacityobjectlabel)  

---

## Create a new semantic tag

### 1. Create the tag ID

__Open `ObjectLabel.h`__ in `LibCarla/source/carla/rpc`. Add your new tag by the end of the enum using the same formatting as the rest.  

![object_label_h](img/tuto_D_create_semantic_tags/01_objectlabel_tag.jpg)

!!! Note
    Tags do not have to appear in order. However, it is good practice to list them in order. 

### 2. Create the UE folder for assets

__Open the Unreal Engine Editor__ and go to `Carla/Static`. Create a new folder named as your tag. 

![ue_folder](img/tuto_D_create_semantic_tags/02_ue_folder.jpg)

!!! Note
    The UE folder and the tag do not necessarily have to be named the same. However, it is good practice to do so.  

### 3. Create two-way correspondence between UE and the code tag

__3.1. Open `Tagger.cpp`__ in `Unreal/CarlaUE4/Plugins/Carla/Source/Carla/Game`. Go to __`GetLabelByFolderName`__ Add the your tag by the end of the list. The string being compared is the name of the UE folder used in [__2.__](#2-create-the-ue-folder-for-assets), so use the exact same name here.  

![tagger_cpp](img/tuto_D_create_semantic_tags/03_tagger_cpp.jpg)

__3.2. Go to `GetTagAsString`__ in the same `Tagger.cpp`. Add the new tag by the end of the switch.  

![tagger_cpp_02](img/tuto_D_create_semantic_tags/04_tagger_cpp_02.jpg)

### 4. Define a color code

__Open `CityScapesPalette.h`__ in `LibCarla/source/carla/image`. Add the color code of your new tag by the end of the array. 

![city_scapes_palette_h](img/tuto_D_create_semantic_tags/05_city_scapes_palette_h.jpg)

!!! Warning
    The position in the array must correspond with the tag ID, in this case, `23u`. 

### 5. Add the tagged meshes

The new semantic tag is ready to be used. Only the meshes stored inside the UE folder of a tag are tagged as such. Move or import the corresponding meshes to the new folder, in order for the to be tagged properly. 

---

## Add a tag to [carla.CityObjectLabel](python_api.md#carla.CityObjectLabel)

This step is not directly related with semantic segmentation. However, these tags can be used to filter the bounding box query in [carla.World](python_api.md#carla.World). In order to do this, the tag must be added to the [carla.CityObjectLabel](python_api.md#carla.CityObjectLabel) enum in the PythonAPI.  

__Open `World.cpp`__ in `carla/PythonAPI/carla/source/libcarla` and add the new tag by the end of the enum.  

![city_object_label](img/tuto_D_create_semantic_tags/06_city_object_label.jpg)


---

Read the **[F.A.Q.](build_faq.md)** page or post in the [CARLA forum](https://github.com/carla-simulator/carla/discussions) for any issues, doubts or suggestions.  

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