Phase 2 — Mesh Segmentation (Blender + 3DSC)

This phase divides the canvas exported in Phase 1 — High-Resolution Mesh Preparation (Metashape) into manageable tiles using the LOD Cutter tool inside Blender. The output is a set of segmented OBJs ready for high-resolution texturing.

2.1 Import Canvas in Blender

  1. Open Blender

  2. Install 3D Survey Collection add-on if not already installed

  3. Import > 3DSC > Import OBJ (Ant File Importer)

  4. Navigate to 05_RB/03_Model_Library/[YourModelName]/meshmono/

  5. Select the OBJ file

img/blender_import_3dsc.png

Fig. 19 [SCREENSHOT: Blender with 3DSC import panel open, showing EM folder structure]

Coordinate Systems

  • Local coordinates: Import directly

  • Georeferenced: Use the shift file option in 3DSC importer to handle large coordinates

2.2 Segment with LOD Cutter

The LOD Cutter tool divides the mesh into manageable tiles:

  1. Select the imported mesh

  2. Open 3DSC > Segmentation panel

  3. Set Grid Size (in m²):

    • Recommended: 60-100 m² per tile

    • Formula for grid dimension: \(\sqrt{\text{Area}}\) (e.g., 8×8m or 10×10m)

    Note

    The grid size should account for both horizontal and vertical surfaces. For architectural models with walls, use smaller tiles (~60 m²) to account for the Z dimension.

  4. Click Cutter set to generate the cutting grid

  5. Adjust grid if needed

img/lod_cutter_grid.png

Fig. 20 [SCREENSHOT: Blender viewport showing segmentation grid overlay on mesh]

2.3 Execute Multi-Cutter

  1. Select the target mesh (active object)

  2. Optional: also select only the cutters you want to use

  3. Open Window > Toggle System Console (to monitor progress)

  4. Save your .blend file first!

  5. Click Multi-Cutter button

The tool will:

  • Use selected cutters, or automatically use all cutters in _cutter if none are selected

  • Cut the mesh into separate objects

  • Assign unique names to each tile

  • Keep cutter objects available for additional segmentation passes

img/multicutter_result.png

Fig. 21 [SCREENSHOT: Mesh segmented into multiple tiles in Blender outliner]

2.4 Clean Floating Geometry

After segmentation, some tiles may contain unwanted floating fragments:

  1. Select a tile

  2. Press Tab to enter Edit Mode

  3. Use K (Knife tool) or select and X > Delete Faces to remove artifacts

  4. Press Tab to return to Object Mode

  5. Repeat for problematic tiles

Tip

Use Alt+Z (X-Ray mode) to see through the mesh and identify floating elements more easily.

2.5 Export Segmented Tiles

  1. Select all tile objects

  2. Open 3DSC > Export panel

  3. Set export folder to 05_RB/03_Model_Library/[YourModelName]/meshpoly/

  4. Uncheck “Relative Path” in export settings

  5. Click OBJ Export Batch

  6. Monitor progress in system console

img/export_meshpoly.png

Fig. 22 [SCREENSHOT: 3DSC export panel with meshpoly folder in EM structure selected]

Best Practice

Save your Blender work file to 05_RB/02_PROCESSING/blender/ with a descriptive name like [ModelName]_segmentation.blend before exporting. This preserves your segmentation work for future reference.

See also