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Activity 002: Multi-Angle Scanning and Scan Alignment

Activity ID: U11M2-ACT-002 Duration: 45 minutes Objective: Learners will execute a complete multi-angle scanning session of a moderately complex object, apply reference targets, perform scan alignment using both target-based and feature-based methods, and produce a unified point cloud with full surface coverage.

Overview

Building on the single-pass scanning skills from Activity 001, this lab introduces multi-angle scanning strategy, reference target placement, and scan alignment. Students work with a more geometrically complex object that cannot be fully captured from a single turntable pass, requiring deliberate planning and multiple scanning orientations.

Materials & Equipment Needed

  • Desktop structured light 3D scanner (calibrated from Activity 001)
  • Complex test object with undercuts and varied geometry (e.g., figurine, mechanical assembly, shoe last, or pottery)
  • Turntable (automated or manual)
  • Adhesive reference targets (coded dots, 3-6 mm diameter, minimum 20 per student)
  • Modeling clay or putty for object repositioning support
  • Computer with scanner software and alignment tools
  • Scanning spray (if needed for object surfaces)
  • Student worksheet (Multi-Angle Scanning & Alignment Log)

Instructions & Procedure

Phase 1: Scanning Strategy Planning (5 minutes)

  1. Examine your assigned object from all angles before touching the scanner:
  2. Identify all surfaces that will be visible from a standard turntable rotation (equator view)
  3. Identify surfaces hidden from the equator view: top surface, bottom surface, undercuts, deep cavities
  4. Sketch a simple scan plan showing how many passes and from which angles you need to scan
  5. Plan reference target placement:
  6. Identify 6-10 locations on the object where targets can be placed on stable, flat areas
  7. Targets must be visible across multiple scan orientations — avoid placing targets that will only appear in one scan
  8. Do not place targets on areas of critical detail you need to capture
  9. Record your scan plan on the worksheet (number of passes, angles, expected total scan count)

Phase 2: Target Application and First Pass (15 minutes)

  1. Apply reference targets to the object per your plan:
  2. Press firmly to ensure adhesion — targets that fall off mid-scan cause alignment failures
  3. Space targets at least 15 mm apart — closely spaced targets confuse detection algorithms
  4. Place 3-5 additional targets on the turntable surface or fixture near the object
  5. Apply scanning spray if needed (reflective or dark areas only)
  6. Execute Pass 1 — Equator scan:
  7. Position scanner level with the object's midline
  8. Set turntable to 20° steps (18 scans per revolution)
  9. Run the automated turntable scan sequence
  10. Monitor the real-time preview for quality and target detection
  11. Verify Pass 1 coverage: Review the accumulated point cloud. Mark missing areas on your sketch.

Phase 3: Additional Passes and Repositioning (15 minutes)

  1. Execute Pass 2 — Elevated angle scan:
  2. Tilt the scanner 30-40° above horizontal (or lower the scanner and tilt the turntable)
  3. Run a second turntable revolution at 20° steps
  4. This captures the top surfaces and upper undercuts
  5. Execute Pass 3 — Object repositioned (if bottom surface is needed):
  6. Carefully invert or reposition the object using modeling clay for support
  7. Ensure at least 4 reference targets from Pass 1/2 are still visible — these bridge the old and new orientations
  8. Run a turntable scan at 20° steps for the newly exposed surfaces
  9. Additional spot scans: If specific areas still show gaps, manually position the scanner for targeted captures
  10. Record total scan count and any issues on your worksheet

Phase 4: Scan Alignment (10 minutes)

  1. Target-based alignment:
  2. Use the scanner software's target alignment function
  3. The software automatically detects coded targets and aligns scans that share common targets
  4. Review the alignment residual (target: < 0.1 mm between scans)
  5. Identify any scans that failed to align — check target visibility and overlap
  6. Feature-based refinement (ICP):
  7. After target-based coarse alignment, run ICP fine alignment
  8. ICP uses the overlapping surface geometry to refine each scan's position
  9. Review the ICP residual (target: < 0.05 mm)
  10. Global registration:
  11. Run global optimization to distribute residual error across all scans
  12. Compare residuals before and after global registration
  13. Final inspection:
  14. Rotate the merged point cloud and check for double-walls, gaps, and alignment artifacts
  15. Cut cross-sections through overlap regions to verify single-surface alignment
  16. Record final alignment statistics on your worksheet

Discussion Points

  1. How did your actual scan plan differ from your initial strategy? What did you have to adapt?
  2. Where did reference targets fail to be detected? What caused the detection failure?
  3. How did the alignment residual change between target-based, ICP, and global registration?
  4. If you had to scan this object again, what would you do differently?

Expected Outcomes

  • A complete multi-angle scan dataset with 90%+ surface coverage
  • Successful alignment of all scans with residual error below 0.1 mm
  • Completed Multi-Angle Scanning & Alignment Log with scan plan, counts, and alignment statistics
  • Practical understanding of the relationship between scan strategy, target placement, and alignment quality

Assessment Rubric

Criterion 4 (Excellent) 3 (Good) 2 (Fair) 1 (Needs Improvement)
Scan Planning Thorough pre-scan analysis; identified all challenging areas; efficient plan Good plan covering major surfaces; minor gaps in strategy Basic plan; missed some undercuts or hidden surfaces No plan; ad-hoc scanning approach
Target Placement Strategic target distribution; targets visible across multiple orientations; no detection failures Good placement with minor detection issues; sufficient for alignment Adequate but clustering or poor visibility caused some alignment failures Poorly placed targets; significant alignment failures
Surface Coverage >95% coverage; minimal occlusion holes; additional passes for problem areas >85% coverage; identified remaining gaps 70-85% coverage; some avoidable gaps <70% coverage or major missing surfaces
Alignment Quality Residual < 0.05 mm; no visible double-walls; global registration applied Residual < 0.1 mm; minor alignment artifacts Residual 0.1-0.2 mm; some visible artifacts Residual > 0.2 mm or alignment failure

Safety Considerations

  • Do not stare into the scanner projector beam during operation
  • Handle reference targets carefully — the adhesive can mark delicate surfaces; test on a non-critical area first
  • When repositioning the object, support it securely with modeling clay — dropping can damage both the object and the turntable
  • Apply scanning spray only in ventilated areas with appropriate PPE (nitrile gloves, safety glasses)
  • Power down equipment when not in active use

Last Updated: 2026-03-19