# Summary of S4-260140: Sport Example for Dynamic 3DGS Content Use Case

## Document Overview

This change request proposes adding a sports scenario example to TR 26.958 to illustrate the Dynamic 3DGS (3D Gaussian Splatting) content use case. The contribution is from Pengcheng Laboratory and China Mobile, targeting the FS_3DGS_MED study item.

## Main Technical Contributions

### Use Case Enhancement - Dynamic 3DGS Content (Section 5.4)

#### Core Use Case Description (Section 5.4.1)

The document enhances the existing Dynamic 3DGS content use case description with the following key characteristics:

- **Content Type**: Time-varying 3DGS content depicting dynamic subjects/scenes (performers, dancers, singers, exhibitions, bands, **sport actions**)
- **Rendering Approach**: Real-time rendering of 3DGS content sequences on the UE
- **Network Support**: Delivery and rendering may be assisted through:
  - Partial delivery mechanisms
  - Network-assisted rendering
- **User Interaction**: Viewpoint adjustment within a constrained navigation volume while the scene changes dynamically
- **Rendering Primitive**: 3D Gaussian splats (as opposed to textured meshes or voxels used in volumetric video)

#### Scope Definition

- **Primary Focus**: Delivery, decoding, and real-time rendering of **pre-recorded** dynamic 3DGS sequences
  - On-demand streaming
  - File download scenarios
- **Future Consideration**: Live dynamic 3DGS capturing and delivery (feasibility-dependent, later stage)
- **Alignment**: Corresponds to TR 26.928 Use Case 3: Streaming of Immersive 6DoF (non-live/on-demand variant)

### Sports Action Example

#### Scenario Description

The CR introduces a **basketball game segment** as an illustrative example (Figure 5.1):

- **Content Representation**: Dynamic scene encoding both:
  - Evolving motion of players
  - Surrounding environment
  - Represented as time-indexed sequence of 3D Gaussian splats

#### Playback Characteristics

- **Temporal Handling**: 
  - UE receives successive temporal segments
  - Continuous rendering to preserve temporal progression
  
- **Spatial Navigation**:
  - User-controlled viewpoint adjustments including:
    - Limited rotation
    - Translation
    - Zoom
  - Enables observation from different perspectives without altering temporal sequence

#### Navigation Constraints

- **Temporal Navigation**: Driven by playback timeline
- **Spatial Navigation**: 
  - User-controlled within permitted range
  - Constrained to **allowed-view volume** derived from original capture configuration
  - Ensures visual coherence and avoids out-of-distribution views
- **Combined Interaction**: Time-continuous playback with interactive viewpoint exploration

## Technical Significance

This contribution provides a concrete, large-scale example for Dynamic 3DGS content use cases, specifically addressing:

- **Wide-area environments** with complex background dynamics
- **Fast-moving subjects** (athletes)
- **Traffic analysis** requirements for extensive 3DGS environments
- **Requirement derivation** for the FS_3DGS_MED study

The sports scenario serves as a representative example for understanding delivery, rendering, and interaction requirements for dynamic 3DGS content in challenging real-world conditions.