How to Measure Your Stairs with Photo-Survey (PS4D)
A step-by-step guide to the fastest, most precise stairlift measurement system in 2025.
- Why Accurate Measurement Matters
A stairlift rail is only as good as the measurements behind it. Millimetre errors lead to:
- Tight spots that bump users’ knees.
- Premature roller wear on curves.
- On-site grinding or spacer shims—delays & dust.
HMK’s Photo-Survey 4-Dimensional (PS4D) system eliminates guess-work and slashes survey time from 45 minutes to under 7 minutes.
- What Is PS4D?
PS4D combines:
- High-resolution stereo cameras mounted on a lightweight pole.
- Target markers placed on each tread (QR-coded).
- SLAM software that converts images into a 3-D point cloud.
- Cloud sync to HMK CAD servers for instant rail design.
Key spec: ±0.5 mm RMS accuracy over 10 m run—verified by TÜV 2024.
- Equipment Checklist
| Item | Qty | Notes |
| PS4D camera pole | 1 | Telescopic, 1–3 m |
| QR stair markers | 40 | Re-usable, adhesive-free |
| Reference calibration board | 1 | Factory-coded |
| Tablet with PS4D app | 1 | Android/iPadOS |
| Laser distance meter | 1 | Cross-check stringer length |
| PPE | — | Shoe covers, gloves |
Homeowner prep: Clear clutter and move breakable décor 50 cm away from stairs.
- Step-by-Step Photo-Survey Workflow
| Step | What Happens | Time |
| 1. Marker placement | Technician places QR markers dead-centre on each tread. | 90 s |
| 2. Calibration shot | Camera captures calibration board at bottom landing. | 20 s |
| 3. Upward scan | Slow sweep from bottom to top; app beeps when coverage 100 %. | 2 min |
| 4. Downward scan | Reverse sweep for redundancy; app auto-stitches. | 2 min |
| 5. Landing & wall shots | Additional photos of sockets, doors, skirtings. | 1 min |
| 6. Validation | App overlay highlights any “red” missed zones; re-shoot if needed. | 30 s |
| 7. Sync | Data uploads via 4G/Wi-Fi to HMK cloud. | 30 s |
Total on-site time: ≈ 7 minutes.
- Data Processing & Rail Modelling
- Point Cloud Generation – 500k+ points with XYZ + RGB.
- Edge Detection – Algorithm isolates tread nosing and stringer line.
- Rail Path Calculation – Software applies safe-clearance envelope (EN 81-40 Annex G).
- CNC Code Export – STEP/IGES file sent to twin-tube bending cell.
- AR Preview – Optional PDF overlay shows homeowner how rail will look.
Average cloud-to-CNC time: < 1 hour for straight rails, < 24 h for curved.
- Accuracy vs Traditional Methods
| Metric | PS4D | Tape + Angle Gauge |
| Linear error (10 m) | ±0.5 mm | ±4 mm |
| Angle error | ±0.1° | ±1° |
| Survey time | 7 min | 40 min |
| Re-visit rate | 0.8 % | 6.5 % |
Lower errors mean the rail fits first time, saving on-site grinding and ensuring a smoother ride.
- FAQ Snapshot
Q: Does PS4D damage my stairs?
A: No. Markers are low-tack vinyl; they peel off without residue.
Q: Do I need bright lighting?
A: The camera uses dual LED panels, but a well-lit hallway speeds up autofocus.
Q: What about spiral stairs?
A: PS4D captures up to 720° of rotation; our Alpha rail handles tight 200 mm inner radius.
Q: Is my personal data safe?
A: Only geometric data is uploaded—no faces or personal items are stored.
