Optical Traceability & VDI/VDE 2634 // Protocol SCL-04
Photogrammetry Scale Bar Validator
Validate certified optical reference scale bars, thermal expansion compensation, point cloud distance deviations (µm), and parts-per-million (PPM) scale accuracy.
24.5 °C
10°C (Cold warehouse)20°C (ISO Standard Reference)40°C (Hot foundry)
From calibration certificate
Distance between target centers
Scale Traceability Output
Relative Scale Error
24.3PPM (µm / m)
Class 2: Shopfloor QA
Scale Deviation (µm)
+19.4 µm
Point-to-point error
Thermal Growth
-1.4 µm
ΔT = 4.5°C shift
True Length at 24.5°C:799.9986 mm
Measured 3D Cloud Distance:800.0180 mm
Linear Residual Delta:0.0194 mm
VDI/VDE 2634 Part 1 Metrology
Optical Scale Bar Physics & Environmental Compensation
1. Parts-Per-Million (PPM) Scale Metric
In photogrammetry, camera bundle adjustments determine relative angular orientations between image frames. A physical scale bar with certified distance $L$ establishes the true metric scale:
PPM = (|L_measured - L_true| / L_true) · 10⁶
A 20 PPM scale error corresponds to 0.020 mm deviation per meter. High-precision automotive body assembly limits global photogrammetry scale drift strictly to under 15 PPM.
2. Thermal Soak & Substrate Coefficients (CTE)
Metal scale bars expand and contract rapidly with workshop temperature swings:
- Aluminum Bars: At 23 µm/(m·K), an uncompensated 5°C ambient shift introduces a massive 115 PPM scale error (0.115 mm/m).
- Carbon Fiber & Invar: Provide immunity to thermal gradients, maintaining certified distance stability even during long photogrammetry capture sweeps.