Accuracy depends on how your data was captured and processed — particularly whether RTK and Ground Control Points (GCPs) were used.
In general, Birdi maps are highly accurate and suitable for monitoring, measurement, and reporting workflows.
However, it’s important to understand the difference between absolute accuracy (how close your map is to true ground elevation) and repeatability (how closely two separate surveys match each other).
When flying with:
RTK only – you can typically expect vertical accuracy of 3–8 cm. However, if you fly the same site on different days without shared GCPs, a vertical difference of up to 10–15 cm (around 0.3–0.5 ft) between surveys is considered normal. This is due to small GNSS variations, satellite geometry, and processing adjustments.
RTK + well-distributed GCPs – vertical accuracy and repeatability typically improve to 2–4 cm. This is recommended for engineering-grade change detection, compliance work, or high-precision volume comparisons.
If you’re comparing pre- and post-surveys and notice small elevation differences in unchanged areas, this is usually not an error — it’s a normal tolerance of RTK-only workflows. Using consistent GCP control across surveys will significantly improve alignment between datasets.
If you’re unsure which workflow is right for your project, our team can help guide you based on your outputs and required precision.
The table below outlines typical industry-expected vertical accuracy and repeat survey variance for drone photogrammetry workflows. These ranges assume good flight planning, adequate overlap, and proper processing settings.
Workflow Type | Typical Vertical Accuracy (Absolute) | Repeat Survey Variance (Between Flights) | Notes |
Standard GPS (No RTK, No GCPs) | 5–15 m | Not reliable for comparison | Suitable for visual mapping only. Not appropriate for elevation or volume analysis. |
Non-RTK Drone + 3–5 GCPs | 2–5 cm | 2–5 cm | Strong repeatability when GCPs are well distributed. Common for engineering and construction projects. |
RTK Drone Only (No GCPs) | 3–8 cm | 5–15 cm | Small vertical bias between separate flights is normal. Suitable for general monitoring and many volume workflows. |
RTK + 1 GCP | 3–6 cm | 4–8 cm | One GCP improves validation but does not fully control vertical alignment across surveys. |
RTK + 3–5 Well-Distributed GCPs | 2–4 cm | 2–5 cm | Considered survey-grade for most engineering, compliance, and change detection workflows. |
PPK + 3–5 GCPs | 2–4 cm | 2–5 cm | Similar performance to RTK + GCPs, with improved consistency in some environments. |
Important Notes
Vertical accuracy is typically weaker than horizontal accuracy in GNSS-based workflows.
Repeat survey variance is often higher than single-survey absolute accuracy due to differences in satellite geometry, atmospheric conditions, and processing adjustments.
For change detection, cut/fill, or compliance work, shared GCP control across all surveys is strongly recommended.
A variance of up to 10–15 cm (~0.3–0.5 ft) between RTK-only surveys is within normal industry tolerance.