Why ground truth doesn’t always require ground points
Jun 2025
Chris Formeller CP, Solution Product Manager, CommercialWhile ground control points are critical for certain high-precision, survey-grade projects, they often aren’t needed for common applications.
Jun 2025
Chris Formeller CP, Solution Product Manager, Commercial)
Picture a large-scale construction project that covers dozens of acres. Every inch counts as a firm maps infrastructure, plans entries, and coordinates utilities. This level of project requires more than basic aerial or GPS data; it needs precise, survey-grade ground truth.
But does achieving precision always require the time-consuming and costly process of deploying Ground Control Points (GCPs)?
Traditionally, GCPs were seen as an absolute must. But the reality is more nuanced. Standards, such as those from the American Society for Photogrammetry and Remote Sensing (ASPRS), reveal that not all applications demand the same level of accuracy, and forcing a “one-size-fits-all” approach leaves room for inefficiency. For example, property assessors need routinely updated imagery at a scale that’s impossibly expensive with GCPs; disaster response requires faster access to post-event insights than GCPs would allow; and initial site analysis of hard-to-reach areas may find it difficult to place GCPs.
In short, GCPs aren’t always the answer.
At Nearmap, we challenge the conventional assumption that GCPs are the ultimate requirement for all aerial imagery — starting with our precision sensors. The Airborne GPS, IMU, and our patented cameras capture accurate position and orientation data right at the source. Then, we leverage our proprietary software, which uses powerful techniques to process that high-quality data and create the final products.
Ground truth without ground points
Positional accuracy is how well the coordinates of features in our imagery match their true positions on the Earth. This is critical for precise measurements, in-depth spatial analysis, and seamless integration with other datasets.
Nearmap imagery is designed from the ground up for high-positional accuracy, and it’s achieved through:
- Advanced sensor technology: Our in-house engineered imaging systems integrate Absolute Global Navigation Satellite System (ABGPS) and high-grade Inertial Measurement Units (IMU). This delivers precise sensor position and orientation data for accurate georeferencing.
- Innovative camera technology: Our proprietary imaging systems, which are patented wide-area aerial cameras, employ advanced multi-resolution and scanning technologies. This approach yields high positional accuracy products that surpass legacy aerial camera systems.
- Proprietary processing techniques: Expert algorithms ensure optimal imagery geolocation through techniques like Precise Point Positioning (PPP) and rigorous bundle adjustments. This meticulous processing minimizes distortion and ensures consistent accuracy across expansive capture areas.
- Quality assurance: Commitment to accuracy doesn’t end with processing. Nearmap continuously validates the accuracy of our imagery against independent, high-precision reference data. Automated checks, quality control inspections, and independent validation ensure that we deliver on our promise of reliable ground truth.
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Meeting industry standards
To talk meaningfully about accuracy, we need a common language. Nearmap adheres to the ASPRS Positional Accuracy Standards for Digital Geospatial Data (Edition 2, Version 2.0). Metrics like Root Mean Square Error (RMSE) ensure we measure, report, and deliver accuracy consistently.
For our 2D imagery, we focus on Horizontal Accuracy (RMSEh). This represents the combined positional error in the horizontal plane (X and Y components), calculated as RMSEh= √ (RMSEx2+RMSEy2). It’s worth noting that older standards often used confidence level metrics like Circular Error 90% (CE90). While we may provide CE90 values for reference, ASPRS Ed2V2 relies solely on RMSE for defining accuracy classes. This shift aims to reduce confusion and improve clarity in how accuracy is reported and understood.
Why ground control points aren’t always needed
While GCPs are critical for certain high-precision, survey-grade projects, they often aren’t needed for common applications. At Nearmap, we use GCPs internally for quality control and validation purposes, but we don’t pass this burden onto our users.
Here’s why you can skip GCPs with Nearmap:
- Independent validation: We use GCPs internally to confirm the accuracy of our imagery against ASPRS recommendations, ensuring you get high-quality data without extra steps.
- Built-in accuracy: By incorporating positional accuracy directly into capture and processing workflows, Nearmap eliminates the need for users to deploy and manage their own GCPs — saving time and costs.
- Out-of-specification handling: If imagery doesn’t hit RMSEh thresholds, it’s flagged. Corrective actions, from reprocessing to data re-acquisition, are used on flagged captures until they meet Nearmap quality standards.
This internal use of GCPs for validation ensures that the accuracy Nearmap states is the accuracy we deliver.
Matching accuracy to use case
ASPRS standards recognize that different tasks require different levels of accuracy. Forcing every project into the highest possible accuracy bracket, often necessitating GCPs, can be inefficient and unnecessary.
The relationship between the imagery’s Ground Sample Distance (GSD), the resulting RMSEh, and its suitability for various tasks is key.
Horizontal accuracy (RMSEh cm) | Recommended use |
|---|---|
≤ 5.0 | High-precision design, critical as-built verification, detailed surveys |
10.0 | Detailed asset management, engineering planning, urban infrastructure mapping |
≥ 15.0 | Site reconnaissance, visual reports, environmental overview, critical infrastructure mapping |
30.0 | Asset management, environmental monitoring, urban planning, general engineering |
≥ 50.0 | Broad area planning, visual reports, environmental studies |
For many applications, the speed of access and consistent quality of Nearmap — achieved through our advanced systems and processing — is often the perfect match.
Fast, consistent & cost-effective
By building accuracy into our capture and processing pipeline, Nearmap offers distinct advantages:
- Speed: Data is available quickly, without the delays of planning, surveying, and integrating project-specific GCPs.
- Consistency: Get accuracy that’s reliable across large areas and refreshed with proactive captures.
- Cost-effectiveness: Save thousands of dollars and invaluable time by skipping the hassle of GCP deployment.
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Trust the process
Ground control points remain essential for applications requiring the absolute highest survey-grade precision. But, for a wide range of industries and use cases, the speed, consistency, and accuracy of Nearmap imagery eliminate the need for routine GCP deployment.
By leveraging proprietary technology, rigorous validation, and adherence to industry standards, Nearmap empowers confident, data-driven decisions — with imagery that’s fit for purpose.