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

Open Blender
Install 3D Survey Collection add-on if not already installed
Import > 3DSC > Import OBJ (Ant File Importer)
Navigate to 05_RB/03_Model_Library/[YourModelName]/meshmono/
Select the OBJ file

img/blender_import_3dsc.png — Fig. 27 *[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:

Select the imported mesh
Open 3DSC > Segmentation panel
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.
Click Cutter set to generate the cutting grid
Adjust grid if needed

img/lod_cutter_grid.png — Fig. 28 *[SCREENSHOT: Blender viewport showing segmentation grid overlay on mesh]*

2.3 Execute Multi-Cutter

Select the target mesh (active object)
Optional: also select only the cutters you want to use
Open Window > Toggle System Console (to monitor progress)
Save your .blend file first!
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. 29 *[SCREENSHOT: Mesh segmented into multiple tiles in Blender outliner]*

2.4 Clean Floating Geometry

After segmentation, some tiles may contain unwanted floating fragments:

Select a tile
Press Tab to enter Edit Mode
Use K (Knife tool) or select and X > Delete Faces to remove artifacts
Press Tab to return to Object Mode
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

Select all tile objects
Open 3DSC > Export panel
Set export folder to 05_RB/03_Model_Library/[YourModelName]/meshpoly/
Uncheck “Relative Path” in export settings
Click OBJ Export Batch
Monitor progress in system console

img/export_meshpoly.png — Fig. 30 *[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.