Lesson Objectives:

1. Define absolute accuracy and relative accuracy in the context of drone mapping.
2. Explain the differences between absolute and relative accuracy.
3. Identify when absolute accuracy is necessary for mapping projects.
4. Describe the role of survey control in achieving absolute and relative accuracy.
5. Evaluate the importance of Ground Control Points (GCPs) and GNSS receivers in ensuring accurate and reliable mapping results.
6. Differentiate between projects requiring high absolute accuracy and those where relative accuracy is sufficient.

Topics Covered:

• Definition and explanation of relative accuracy in drone mapping.
• Key differences between absolute accuracy and relative accuracy.
• The role of survey control in achieving high accuracy.
• Importance of Ground Control Points (GCPs) and checkpoints.
• How GNSS equipment contributes to accurate and precise mapping.
• Applications of absolute accuracy in engineering and construction projects.
• When relative accuracy is sufficient for visualization and marketing purposes.

Understanding Absolute and Relative Accuracy in Drone Mapping

Now that we’ve clearly defined accuracy and precision, let’s do a quick review of relative accuracy versus absolute accuracy and how these concepts will play into the rest of this course. These two types of accuracy are fundamental to understanding how survey control impacts your drone mapping projects, so it’s essential to get a solid grasp of the differences between them.

What is Absolute Accuracy?

Let’s start with absolute accuracy. Absolute accuracy refers to how close the measurements in your map or model are to their actual positions in the real world. In other words, it’s a measure of how well your data is tied to real-world geographic coordinates. For example, if you’re mapping a construction site, absolute accuracy ensures that every feature, whether it’s a building, a road, or a plot boundary, is positioned exactly where it’s supposed to be on the Earth’s surface, down to the centimeter or foot.

Visual: A 3D model of a construction site, with coordinates aligning perfectly with real-world locations.

Absolute accuracy is critical when your drone data needs to be integrated with other geographic data sets, like existing engineering designs, GIS data, or maps from other surveys. In these cases, even small positional errors could cause big problems, especially in fields like construction, land development, and engineering.

Visual: Construction plans overlaid on a drone map, demonstrating perfect alignment.

What is Relative Accuracy?

Next, let’s talk about relative accuracy. Relative accuracy refers to how consistent the measurements are within your map or model, compared to one another. It focuses on the relationships between the points and features in your dataset, regardless of their absolute positions in the real world.

Visual: A cluster of buildings and roads in a 3D model being shown in perfect proportion to one another, regardless of their overall location.

For example, if you’re mapping a group of buildings, relative accuracy ensures that the distances between the buildings are correct, even if the entire model is slightly shifted off from its true position on the Earth. As long as everything in your map is in the right proportion and spatial relationship, you’ve achieved high relative accuracy.

Visual: The same buildings in a model being slightly shifted on the map, showing high relative accuracy but low absolute accuracy.

How Do They Relate to Survey Control?

So, how do absolute and relative accuracy relate to survey control? Well, in drone mapping, survey control helps to achieve both, but it’s typically the most essential with absolute accuracy. Let’s break it down.

Visual: A surveyor setting up Ground Control Points on a site, followed by a GNSS receiver capturing data.

To achieve high absolute accuracy, you need to tie your drone data to real-world coordinates, and this is where Ground Control Points or checkpoints come into play. When you use GCPs — which are precisely measured with GNSS receivers — you’re ensuring that your drone images are positioned exactly where they should be on the Earth. In other words, survey control ensures that your map or model is anchored to true geographic coordinates, which is critical for projects that require high absolute accuracy.

Visual: A map being adjusted with Ground Control Points to align perfectly with real-world coordinates.

But even if you’re not using GCPs and only care about relative accuracy, survey control still helps. The natural accuracy of your drone and camera will often be good enough to maintain high relative accuracy. The spatial relationships between points — such as distances between buildings, heights, or volumes — will remain consistent within the map, even if it’s slightly misaligned with the real world.

Visual: A map being processed without GCPs, showing high internal consistency.

When Do You Need Absolute vs. Relative Accuracy?

So, when do you need absolute accuracy, and when is relative accuracy enough? This depends entirely on the project. If you’re working on a project where the map needs to integrate with other data — such as engineering plans, property boundaries, or infrastructure layouts — absolute accuracy is a must. This is where survey control with GCPs, GNSS receivers, and checkpoints is critical.

Visual: A detailed construction project map being compared to an engineering design, requiring high absolute accuracy.

However, for smaller projects where exact geographic locations aren’t crucial — like generating 3D models for visualization or marketing purposes — relative accuracy might be enough. As long as the internal distances and proportions are correct, the exact position on the Earth may not be as important.

Visual: A real estate development 3D model used for marketing purposes, showing high relative accuracy.

Conclusion

In summary, absolute accuracy ties your map to real-world coordinates, while relative accuracy ensures that the features within your map are proportionally correct. Survey control, especially through the use of Ground Control Points, Check Points, and GNSS equipment, is what helps you achieve high levels of verifiable absolute accuracy. Understanding the difference between these two types of accuracy will help you know when to apply survey control techniques to your drone mapping projects.

Quiz