SpatialLM is a 3D large language model designed to process 3D point cloud data and generate structured 3D scene understanding outputs. The system provides end-to-end tools for indoor scene understanding, including layout estimation (walls, doors, windows) and 3D object detection (furniture and indoor objects). The architecture consists of a modular Python library with CLI entry points for inference, training, evaluation, and visualization. It combines point cloud encoders (SceneScript or Sonata) with LLM backbones (Llama or Qwen variants) through a projector network. The system handles the complex task of aligning 3D geometric data with language understanding to produce structured outputs representing architectural layouts and object bounding boxes. Key innovations include the use of space-filling curve encodings (Hilbert and Z-order) for positional encoding in the point cloud transformer, a composable transformation pipeline for point cloud preprocessing, and a sophisticated layout representation system that handles the discrete/continuous coordinate transformations required for architectural elements.