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We often hear this question:
**"How accurate is the 3D model I create using visual data from the Elios 2?"**
This is a bit complex, as the accuracy of your 3D model relies heavily on the precision of the data used to construct it. However, there’s a general rule that applies to any 3D model or dataset:
The theoretical maximum accuracy of a 3D model built using visual data from the Elios 2 is three times the Ground Sampling Distance (GSD), which refers to the size of pixels as they appear on the model's surface.
Given the Elios 2's 4K camera, you can achieve a maximum GSD of 0.25 mm/pixel. Consequently, the most precise 3D model you could theoretically generate would have an accuracy of 1 mm (though it would actually be 0.75 mm, we round up for simplicity).
Take a look at this video demonstrating how such accuracy can be achieved using reference dimensions near the measured objects to scale the model:
[Embedded Video]
Here are some highlights from the video:
- It showcases an experiment conducted under ideal conditions, with no backlighting and on a non-reflective surface rich in texture.
- We focused on modeling a small area (approximately 0.5 square meters) to measure small objects less than 5 cm in size.
- Two scale constraints and one orientation constraint were established throughout this area.
- Test measurements were taken very close to the scale constraints.
- The model wasn't referenced to any specific coordinate system, so we evaluated its relative accuracy.
Key Considerations About Accuracy in a 3D Model Made with Elios 2 Visual Data
Even though the video shows you can achieve up to 1 mm accuracy with the Elios 2, this level of precision may not be practical—or even necessary—for every project.
Your desired accuracy should always be factored into the project planning phase, determined by the intended application of your 3D model. If you need to pinpoint the exact proximity of one part of an object to another with high precision, you'll want to plan meticulously, fly close to the object, and gather the best possible data.
Conversely, if you just need a general idea of how elements relate to one another on a surface, you don't need to spend as much time planning or getting as close as possible.
[Related Reading: Why use photogrammetry to build 3D models of indoor spaces?]
Regardless, the quality and accuracy of your 3D model hinge entirely on the quality and accuracy of the data you collect and use to build it.
Some important considerations for ensuring accuracy include:
- Larger areas require more reference points (referred to as "scale constraints" in Pix4D).
- The closer you can get to the object, the better the accuracy.
- Proper lighting is crucial; dust and poor lighting will degrade image quality.
- Calibration ensures smooth drone movement and clear images.
- Reflective surfaces pose challenges due to fewer distinguishable features.
![Large-Space Photogrammetry]
The Importance of Ground Sampling Distance (GSD) Resolution
Ground Sampling Distance (GSD) measures the distance between the centers of two adjacent pixels on the observed object. Typically expressed in mm/px, a GSD of 1 mm/px indicates that one pixel in the image corresponds to 1 mm in the real world.
Unlike pixel resolution, GSD depends on the camera-to-object distance. As the camera moves closer to the object, the GSD improves (smaller values).
A smaller GSD results in a larger object representation, revealing finer details.
[3D Model Accuracy Example]
Photogrammetry is inherently scale-related. Thus, the closer you can get to the object or area being mapped, the higher the accuracy of your model.
The Elios 2’s unique cage design allows it to fly very close to objects, making it a powerful tool for creating high-quality 3D models. In the video, the Elios 2 flew just 20 cm (7.8 inches) from the surface.
However, the GSD should align with your project’s requirements. There’s always a trade-off between accuracy and efficiency. High accuracy demands flying close and taking more time, while lower accuracy allows for faster coverage.
Did you know?
The Elios 2 can capture images with a GSD of 0.18 mm/px (0.007 in/px) at a distance of 30 cm (11.8 in).
Three critical resolutions to consider are pixel resolution, GSD resolution, and spatial resolution—learn more about the Elios 2’s camera performance in these areas.
GSD Fisheye Lens Considerations
When using a fisheye lens, GSD also depends on the object's position within the image, not just the distance from the camera. Objects in the center appear larger (smaller GSD), while those in the corners appear smaller (larger GSD).
Use Cases and Accuracy
It’s vital to consider the required accuracy early in your mission planning. For instance, land surveys require less precision compared to indoor inspections, where knowing the exact distance between a weld and an entryway is critical.
For example, when identifying defects in a 500 mm duct using the Elios 2, you’d want sufficient accuracy to ensure safe access nearby.
Planning must consider the use case to determine the appropriate accuracy.
[Case Study: Elios 2 Tested for Stockpile Volumetry]
Want to Learn More?
Here are some resources to deepen your understanding of photogrammetry with the Elios 2:
- [Webinar] Indoor 3D Modeling Use Cases: Photogrammetry in Action
- [Webinar] Indoor 3D Modeling: Applications & Implications
- [Article] Why use photogrammetry to build 3D models of indoor spaces
- [Article] Building 3D models with Elios 2: How to Acquire Appropriate Data for Photogrammetry
- [Article] Building 3D models with Elios 2: Processing Data with Photogrammetry Software
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June 20, 2025