SLPK (Scene Layer Package)

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Introduction

SLPK (Scene Layer Package) file format is a file format used to store and share 3D scene data. The SLPK file is a packaging format in ArcGIS Pro software, which is used to package 3D scene data and related resources into a single file for easy sharing and transmission on the ArcGIS platform.

File Structure

Overall structure

**Essence: **a ZIP compressed package (but the internal files are not compressed additionally, only encapsulated in ZIP format).
Core files:
- 3dSceneLayer.json: description file (such as coordinate system, data range, version).
- nodes/: folder for storing 3D node data.
- sharedResources/: folder for shared resources (such as textures and materials).

Nodes

**Function: **The 3D scene is divided into multiple nodes (similar to the “blocks” of the map), each node contains:
- Geometry data (.bin file): stores information such as vertices and patches of the 3D model.
- Texture map (.jpg/.png): surface material of the model.
- Attribute data (.json): additional information of the node (such as ID, name).
LOD (multiple levels of detail): A node may contain multiple LOD versions, and models of different precisions are dynamically loaded according to the distance.

Shared resources

Reuse mechanism: Textures, materials and other resources may be shared by multiple nodes and stored in sharedResources/ to avoid duplicate storage.
Reference method: Nodes reference shared resources by path or ID to reduce file size.

Bounding Volume

Function: Define the spatial range of the node, similar to a “box” to wrap node data, for fast rendering and query.
Type:
- OBB (Oriented Bounding Box): Suitable for regular shapes (such as buildings).
- MBS (Minimum Bounding Sphere): Suitable for irregular data such as point clouds.

Version Difference

I3S 1.7+: Node index information is aggregated into nodePages to reduce the number of files and improve loading efficiency.
**I3S 1.8+: **Support Basis Universal texture compression to further optimize storage and rendering.

Analogy

SLPK file ≈ a bound book:
- 3dSceneLayer.json ≈ cover (records book information).
- nodes/ ≈ book pages (each page is the data of a node).
- sharedResources/ ≈ public illustration library (pictures shared by multiple chapters).

Pros

Efficient storage and transmission: Compression algorithms and spatial indexing technology are used to reduce file size and improve loading speed. Supports multi-level of detail (LOD) rendering to optimize the display performance of large-scale scenes.
Cross-platform compatibility: Can be used in multiple Esri products such as ArcGIS Pro, ArcGIS Online, ArcGIS Earth, etc., supporting cross-platform sharing and collaboration.
Data integrity: Encapsulates 3D models, textures, metadata and other resources into a single file to avoid data loss or version inconsistency.
Supports multiple data types: Can store multiple 3D data types such as oblique photography, point clouds, 3D objects (such as BIM models), integrated meshes, etc.

Cons

Dependence on the Esri ecosystem: SLPK is an Esri proprietary format. Non-Esri software (such as QGIS, Blender, etc.) may not be able to read or edit it directly, and must rely on tools or plug-ins provided by Esri.
High learning cost: Creating and editing SLPK files requires familiarity with tools such as ArcGIS Pro or CityEngine, which has a certain threshold for non-professional users.
The file size is still large: Despite compression, the SLPK file size of high-precision three-dimensional scenes (such as large-scale urban models) may still be large, affecting transmission and storage efficiency.
Limited openness: Compared with open formats such as glTF and OBJ, SLPK is less open, which may limit its application in non-Esri ecosystems.

Application Scenario

By using SLPK files, urban planners and designers can create and share realistic city models for planning and evaluating urban development projects. SLPK files can also integrate various geographic data and provide powerful analysis tools to help users perform geographic analysis and decision support.