0 3 -- Scanning Workflows

Applies to: C1 and S20 (unified unless noted)
Related: Master Index | 01-Hardware-Setup | 04-3DGS-Workflow | 06-RTK-GCP

---

Before You Scan

Pre-Scan Checklist

1. Charge phone -- no low-battery warning exists; phone can die mid-scan
2. Format MicroSD card via SHARE Capture app (on C1), not via Windows
3. Select scan mode: Point Cloud or 3DGS (see below)
4. Plan your route -- identify feature-rich areas for initialization and loop closure
5. Check lighting -- cloudy/overcast is ideal; avoid full sun

Scan Mode Selection

Mode	Photo Interval	Use Case
Point Cloud	C1: 0.2s S20: 0.5s	LiDAR + sparse photos for coloring. Lighter files.
3DGS	Both: fixed at 0.5s	Dense photos for Gaussian splat generation. C1 can select 0.2s by choosing Point Cloud mode, not 3DGS (iris.digital.pl)

C1 advantage: Can get 0.2s interval by selecting "Point Cloud" mode. GS mode is fixed at 0.5s for both devices.

---

Environmental Conditions

Ideal

• Cloudy/overcast -- "Perfect cloudy day" is the gold standard (iris.digital.pl, tool_guy_365)
• Grey skies, short sun peeks are fine
• Start in feature-rich area -- edges, corners, furniture, textured surfaces (ser0ka)

Problematic

• Full sun -- causes overexposed images, clipped highlights, washed-out colors
• Mirrors and glass -- create false reflections, duplicate geometry
• LED advertising boards -- changing content causes reconstruction failures. Use automasker but "it's trouble anyway" (iris.digital.pl, avsupport)
• Plain walls, empty rooms, long corridors -- minimal SLAM features = drift buildup
• Repetitive patterns -- symmetric or uniform surfaces fail SLAM tracking

Dealing with Problematic Environments

• Cover mirrors before scanning (ser0ka)
• Scan mirror rooms as separate scan, clean up individually, merge later
• For LED boards: scan from angles that minimize their presence in images

---

Movement & Technique

Core Principles

1. "Scan with your legs, not your arms" (ser0ka)
2. Move around objects to create parallax
3. Small, controlled rotations are fine -- large/fast swings hurt tracking

4. Smooth motion + good coverage from different positions = stable SLAM

5. Speed: Keep movement under 1 m/s -- slow and consistent

6. Hold scanner front and center of body -- minimizes operator appearing in images (tool_guy_365)

7. Move scanner up and down as you go -- more coverage + extra parallax (iris.digital.pl)

8. Hold still at key points -- point camera at details you want to capture, pause briefly (iris.digital.pl)

Loop Closure Strategy

DO: Multiple small loops with good overlap
DON'T: One giant loop with minimal variation

Recommended pattern:
1. Start in a feature-rich area
2. Create multiple small loops throughout the scan
3. Regularly return to central/feature-rich areas
4. Close the loop at the end (walking back over start point)
5. Walk around objects (tables, cars, furniture) rather than past them

Turning Around

• Don't pivot sharply on the spot
• Make wide U-turns like "a six-point turn instead of a 3-point turn" (iris.digital.pl)
• In confined spaces: go slightly to the side, stop before wall, go back a bit but to other side -- like U-turning a car

---

Scan Strategies by Environment

Interior Scans

1. Initialize in room with most features (furniture, corners, textures)
2. Multiple small loops room by room
3. Return to central areas between rooms
4. Walk around objects, not just past them
5. Scan bathrooms with mirrors separately -- clean up noise, merge later
6. Hold still at doorway thresholds to capture strong geometry transitions

Exterior Scans

1. Stay relatively close to building for good reference
2. Don't just do one big loop -- scan one side, partially walk back, continue to next side
3. Incorporate all doors/entrances to strengthen interior-exterior connection
4. Walk around lamp posts, parked cars, entrance features

Multi-Scan Projects (Interior + Exterior)

1. Separate interior and exterior scans (paulosilva3d, ser0ka)
2. Initialize both from same starting point outside a door -- makes alignment much easier (tool_guy_365)
3. Capture all GCPs outside first, before going inside (ser0ka)
4. Keep interior scan clean and continuous -- don't go in and out repeatedly
5. Use CloudCompare for alignment (see 08-Third-Party-Tools)
6. Erase noise from interior scans that bleeds outside walls

Large Open Areas (No RTK)

Football field / sports field is worst-case SLAM scenario:
- Long distances, little vertical structure, repetitive markings, few features
- DO NOT attempt as one giant continuous scan without RTK
- Break into smaller sections with strong reference areas (sidelines, bleachers, structures)
- Use multiple partial scans with control points
- Expected result: ~30,000 m = serious drift risk without RTK

Tight Spaces (Boats, Bathrooms)

• Realtime drift is common in tight spaces -- panic is normal (mr_red1991_63830)
• Stand still -- let SLAM recover
• Walk very slowly
• Minimize turns in confined areas
• If scan goes completely haywire: stop, restart from a feature-rich recovery point

Multi-Story / Sloped Floors

• Two-floor buildings with sloped ramps: algorithm struggles -- tries to make sloped surface straight (lucapoia)
• Going on roof during scan: Can corrupt entire processed result -- scan looks fine on phone but is twisted after processing (tool_guy_365)
• Strategy: Go on roof EARLIER in scan to detect issues sooner

---

Scan Duration Guidelines

Duration	Point Cloud	3DGS
2-10 minutes	Reliable	Reliable in PCS
10-20 minutes	Good	May fail in PCS -- use external tools
20-30 minutes	Good (recommended max)	Universally fails in PCS -- must use Reality Capture + Postshot
30+ minutes	IMU drift accumulates	Not recommended

File sizes for planning:
- 20-minute outdoor scan 13 GB raw data (tool_guy_365)
- 32-minute outdoor scan 19.3 GB raw data (tool_guy_365)

---

Auxiliary Photography

When to Add External Photos

• Scans >10 minutes (3DGS will fail in PCS -- need external pipeline)
• High-detail areas (signage, artwork, architectural details)
• Low-light areas where C1/S20 cameras struggle

Recommended Gear

• Sony a7rIII with 14mm or 35mm lens on tripod (iris.digital.pl)
• Phone photos on auto settings -- just walk a loop with phone
• Tripod matters -- "it's a hustle to carry but it really makes a difference" (iris.digital.pl)

Technique

1. Scan normally with C1/S20 at 0.5s interval (GS mode)
2. At "hero spots," stop and take phone/camera photos all around
3. A simple circle around the subject with tripod-mounted camera = excellent supplementary data
4. In Postshot, photometric compensation averages all photos -- so auto settings on phone are fine

Shutter Speed

• 1/100 is the confirmed threshold -- slower = motion blur bad for 3DGS (avsupport, olahaldor)
• High ISO introduces grain -- tradeoff: grain vs blur (avsupport)

---

Scooter / Vehicle Scanning

• Viable for consistent speed on long routes
• Watch for speed warnings (especially downhill)
• Operator's arm/clothing appears in images -- yellow high-vis shows in point cloud
• Hold scanner off to side while operating vehicle
• Best practice: stand sideways on scooter, hold scanner front and center

---

Best Practices Summary

1. Cloudy day > sunny day
2. Multiple small loops > one big loop
3. Feature-rich initialization > empty room initialization
4. Separate interior + exterior scans > single combined scan
5. Slow and steady > fast
6. Scan with legs > scan with arms
7. Hold still at detail points
8. Move scanner up and down as you go
9. Cover mirrors / scan separately
10. Computer sleep OFF during processing
11. Undistorted Photo Output OFF for faster processing