terrain-cleanup-pipeline

Terrain Cleanup Pipeline

Overview

Processes raw photogrammetry terrain tiles from Metashape into clean, classified, UV-mapped meshes ready for game engine export. This is the core workflow for Real Sim Roads.

Golden Rules

1. NEVER remove upward-facing faces (normal.z >= 0) - these ARE the terrain
2. NEVER alter object-level transforms on Tile_* objects
3. ALWAYS save after every phase - Blender crashes happen
4. Process max 10 tiles per tool call to avoid timeouts
5. Verify results after each phase before proceeding

Phase 1: Assessment

Tool: classify_surfaces(object_name)

For each tile:

1. Call classify_surfaces with default thresholds (road > 0.85, cliff 0.2-0.85, vegetation < 0.2)
2. Calculate canopy percentage: vegetation_faces / total_faces
3. Categorize:
   • < 2% canopy: SKIP (clean enough)
   • 2-5% canopy: MARGINAL (basic cleanup only)
   • 5-15% canopy: MODERATE (basic + targeted envelope)

   • 15% canopy: HEAVY (full envelope, may need manual review)

Phase 2: Basic Cleanup

Tools: separate_loose, remove_faces

For MARGINAL, MODERATE, and HEAVY tiles:

1. separate_loose(object_name, keep_largest=True) - remove disconnected fragments
2. remove_faces(object_name, normal_threshold=-0.2) - remove downward-facing + high faces
3. separate_loose(object_name, keep_largest=True) - clean up post-cut fragments
4. Delete tiny resulting objects (< 500 faces)
5. save_file()

Phase 3: Targeted Envelope

Tool: compute_envelope

For MODERATE and HEAVY tiles only:

1. compute_envelope(object_name, grid_res=3.0, height_threshold=4.0)
2. separate_loose(object_name, keep_largest=True) - post-envelope cleanup
3. save_file()

Parameters:

• grid_res=3.0 - ray grid spacing in meters (smaller = more precise, slower)
• height_threshold=4.0 - faces this far above ground are canopy

Phase 4: Re-Classification

Tool: classify_surfaces

1. classify_surfaces(object_name) on all processed tiles
2. Verify canopy is now < 2% on all tiles
3. If any tile still > 5%: flag for manual review
4. Surface groups are now ready for per-group operations

Phase 5: UV Projection

Tool: project_uv

1. project_uv(object_name, direction="top_down") on all tiles
2. Verify UV layer was created
3. save_file()

Phase 6: Optimization (Optional)

Tool: decimate_mesh

Only if tiles exceed target face count:

1. Target: 500k-2M faces per tile
2. For tiles > 2M faces:
   • decimate_mesh(object_name, target_count=1000000)
3. save_file()

Workflow Summary

For each tile:
  Phase 1: classify_surfaces -> determine category

  If SKIP: go to Phase 5
  If MARGINAL: Phase 2 -> Phase 4 -> Phase 5
  If MODERATE: Phase 2 -> Phase 3 -> Phase 4 -> Phase 5
  If HEAVY: Phase 2 -> Phase 3 -> Phase 4 -> check if < 5% -> Phase 5

  Phase 6: if faces > 2M

  save_file after every phase

Common Pitfalls

• Removing terrain faces: If normal_threshold is too aggressive, you'll cut into hillsides. Start conservative (< -0.2).
• Envelope on sparse meshes: If the tile has large gaps, the raycasting grid may miss ground. Use smaller grid_res.
• Timeout on large tiles: Tiles with > 4M faces may timeout during envelope. Process these individually.
• Order matters: Always do basic cleanup before envelope. Envelope is expensive and works better on pre-cleaned meshes.