The reliability of volumetric outputs depends on the resolution and quality of input data, as well as the accuracy of polygon boundaries. External variables, such as data inconsistencies, terrain complexity, and incorrect layer assignments, may introduce errors in calculations. To ensure precision, users should validate results against field measurements when accuracy is critical.
Key Factors Affecting Accuracy
Drone and Sensor Quality
A high-quality drone with a calibrated camera (e.g., DJI Phantom 4 Pro, Mavic 3 Enterprise) will produce better results.
Wide-angle or fisheye lenses can introduce distortions that affect accuracy.
Flight Planning
Higher Overlap (80% front, 70% side) improves photogrammetry model quality.
Lower altitude flights (~50-100m) increase resolution and improve measurement precision.
Consistent lighting and low wind conditions reduce distortions.
Processing Software and Algorithm
Platforms like Birdi, Pix4D, DroneDeploy, and Agisoft Metashape use advanced photogrammetry techniques to improve measurements, even without GCPs.
Some software offers scale constraints to improve volumetric accuracy without RTK/GCP.
Feature Type and Structure Complexity
Buildings with clear, well-defined edges are easier to model accurately.
Complex structures, reflective surfaces (glass, metal), or occlusions (overhangs) reduce accuracy.
Comparing Methods for Improved Accuracy
Method | Expected Accuracy (XYZ) | Volumetric Error |
No RTK, No GCP | ~10-20% | ~5-15% |
RTK/PPK Drone Only | ~2-5 cm | ~2-5% |
GCPs (5+ well-placed) | ~1-3 cm | ~1-3% |
RTK + GCPs | <1-2 cm | <1-2% |
How to Improve Accuracy Without RTK/GCP?
Potential Accuracy Without RTK/GCPs
Relative Accuracy (Internal Consistency): ~2-5% error
The relative accuracy of the volumetric model (the consistency of measurements within the same dataset) can be reasonably high, assuming good overlap, proper flight patterns, and high-quality image processing.
Absolute Accuracy (Real-World Alignment): ~10-20% error
Without GCPs or RTK, absolute accuracy (alignment to real-world coordinates) is lower, potentially leading to significant errors in position and scale.
Improve accuracy without RTK/GCP
Use known scale references (e.g., place a measured object of known size in the scene).
Manually align models to known reference points in software.
Ensure consistent flight altitude and overlap for better model reconstruction.
If relative measurements (e.g., comparing two time periods) are enough, you might be fine without RTK/GCPs. However, if you need precise real-world alignment (e.g., for engineering, compliance, or billing), RTK or GCPs are recommended.
How accurate is tonnage?
Tonnage is your calculated volume multiplied by a density, so it carries two sources of error, not one:
Volume error. Everything on this page applies. A 5% volume error is a 5% tonnage error.
Density error. Library densities are industry-standard figures for loose material in typical condition. Real density varies with moisture, compaction, particle size and how the pile was built. A difference between 1.6 and 1.8 t/m³ is a 12% swing in the tonnage.
For monitoring and planning, library densities are fine. If the number is going on an invoice, a royalty return or a haulage contract, use a density measured from your own material and add it as a custom material.