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How Accurate is the Land Surveying Using Drones

A Centimeter Level Detailed Land Survey of a Chemical Factory

Drones come in many shapes and sizes. Commercial drones are available in the copter and fixed-wing planes, capable of capturing digital images and videos using both remotely controlled and autonomous flights. They have become a major part of our lives in many aspects including photography, videography and most importantly field mapping. It can map a larger area in minutes where the human takes hours, days and weeks.

The procedure to produce the 3D model of the field includes, acquiring digital images with sufficient overlaps between them using drones, collection of Ground Control Points (GCPs) and Check Points (CPs) using high precision Global Navigation Satellite System (GNSS) receivers or Total Station, processing of digital images along with GCPs, and analysis of result and CPs.

The accuracy of the land survey depends upon the final application. In some cases, 30 centimeter of error is acceptable, on the other hand, sometimes it is required to have 2 centimeter level of accuracy.

Number of Overlapping Images Computed for each Pixel of the Orthomosaic.

The degree of accuracy of the drone-based photogrammetry relies on various technical factors. These include sufficient overlaps of images, field profile, stabilize camera platform, visibility of the field, and GNSS signal conditions. These aspects must be taken care of, otherwise, it can deteriorate the desired outcome.

If these conditions are met sufficiently then the produced results are considered accurate. However, sometimes a look-alike model does not represent the actual localized information and misleads to surveying data. Therefore, it is required to analyze the 2D keypoint matching and CPs error results.

A 2D keypoint matching result identifies the density of keypoints matching of the drone images. The darker area of this profile shows the strong matching of keypoints and represents higher accuracy results, whereas, the brighter area requires manual tie points or more images and represents lower accuracy compared to the darker one.

Computed Image Positions with Links Between Matched Images.

CPs error results are produced in a table format to identify the difference between GNSS based collected CPs and the position computed from the produced 3D model. Since each point on the produced 3D model cannot be verified by GNSS receiver therefore, a normal probability distribution function is used to analyze the CPs error results over the field. These curves illustrate the probability of error in all three X, Y, and Z direction. This is the reason, it is suggested to collect the GCPs and CPs all over the terrain profile. By analyzing these results, the accuracy of the mapped area can be determined.

Probability Distribution Function of CPs Error Results.

In this post we analyzed different factors affect land surveying using drones. We also overviewed how the accuracy of the produced results be checked.

AZ NavTeq provides drone-based commercial surveying & mapping services. Our engineers are expert in photogrammetry based surveying campaigns and produce the most possible accurate results of the land survey.

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