What is accuracy?

 

Some people tell me that accuracy in drone mapping is everything but what do we mean by accuracy?

Essentially it refers to how close the data on the screen relates to what is on the ground or to each other.

But accuracy is more than just the word or phrase, and, in some ways, it has more than just one meaning so I am going to try a explain what it means in photogrammetry and to do this ill need to split this into several posts over the next few weeks:

I suppose the first point to understand is how do you define accuracy?

In drone mapping, accuracy refers to how closely the data collected by the drone matches the true dimensions and features of the area being mapped. For me this can be split into 4 different types.

1.            Absolute Accuracy is about how close the screen coordinates are to the real-world coordinates on earth’s surface. It can be measured as the RMSE (Root Mean Square Error) score given at the end of processing. It is useful in resolving boundary issues or for creating accurate GIS (Geographic Information System) data.

2.            Relative Accuracy is about how accurate the data is within the confines of the area covered. In other words, it’s about how accurate the positions of the features, within the data set, are relative to each other. It’s important for tasks such as creating detailed 3D models or tracking changes over time.

3.            Local accuracy is similar the relative accuracy in many ways, but it usually means that the data set is collected using a local grid system (not OSGB1936 ETRS89 for example). It refers to a smaller area within the original data set and focuses on how the screen data compares to the true measurements of the features in the smaller area. It’s best used when detailed, fine-scale mapping is required for tasks such as construction site surveys, archaeological digs, or infrastructure inspections.

4.            Global accuracy like absolute accuracy it is about how the screen data represents the real world. It considers the accuracy of the entire data set unlike Local accuracy but can have less detail. It’s crucial for tasks such as creating accurate maps, orthomosaics, or GIS datasets that represent the entire surveyed area.

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Other defining factors in accuracy?

 

What do I mean when I say defining factors. In the case of accuracy, they are other considerations to be taken into account, all are interrelated and can be prioritised depending on the reason for the flight.

Horizontal Accuracy. How accurate the drone's measurements are in the horizontal plane. Expressed in meters or feet on the X and Y coordinates.

Vertical Accuracy: How accurate the drones’ measurements are in the vertical plane. Expressed in meters or feet on the Z coordinates.

Temporal Accuracy: This relates to the precision of data captured at different times, particularly important for monitoring and tracking changes over time.

Geometric Accuracy: is all about the fidelity of shapes, angles, and distances within the data set.

Radiometric Accuracy: Is all about the fidelity of the colours and brightness values in the imagery. This ensures the image is balanced and colour matched across the entire data set and represents the colours on the ground.