Relative vs Global Accuracy
Global Accuracy
Refers to how well the reconstructed model aligns with real-world coordinates (latitude, longitude, elevation).
Critical for survey-grade mapping, GIS integration, and legal documentation.
Achieved using:
Ground Control Points (GCPs)
RTK/PPK GNSS corrections
Without GCPs or GNSS corrections, global accuracy can be off by meters.
Relative Accuracy
Measures how accurately features are positioned relative to each other within the model.
Important for distance, area, and volume measurements (e.g., stockpiles, building dimensions).
Can be high even without GCPs, especially with good image overlap and low GSD (Ground Sampling Distance).
Doesn’t guarantee correct placement on Earth’s surface.
Comparison
Reference System
Earth based coordinates
Internal model consistency
Use Cases
Surveying, GIS, legal documnets
Measurements, inspections
Key Tools
GCPs, RTK/PPK GNSS
Accuracy Range
1 - 3cm
2 - 6cm (within the model)
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