3D Surveying of Castles with a Drone using Photogrammetry and 3D Laser Scans from LOGXON
For many towns, communities and regions, castles are important architectural monuments, cultural property and part of accumulated cultural heritage. Economically they mainly play a big role in the field of tourism. For this reason, people are very interested in preserving a castle’s current condition and archiving it for the future. The 3D surveying of castles with a drone using photogrammetry and 3D laser scans is playing an ever greater role in this regard because, if renovation measures are required or reconstructions are to be made to historic buildings, for example, then precise bases for planning are needed. This also applies to (damage) documentation in the field of monument care and protection.
During the 3D surveying of castles with a drone using photogrammetry in combination with 3D laser scans, we carry out contiguous and detailed condition scanning. During the surveying, inner rooms, external areas, the castle courtyard or the entire castle complex can be surveyed and mapped in a 3D point cloud.
The two methods photogrammetry (photogrammetric scanning with a drone or also terrestrially) and 3D laser scanning enable the complete geometric surveying of difficult building complexes in the shortest possible time. When surveying a castle or a castle complex, it is simultaneously visually documented with high-resolution images.
The 3D surveying of castles is a measurement that takes account of every deformity and stone. The survey is the basis for further processing, historical analysis, inspection by experts or renovation.
Results from a 3D survey of castles with a drone using photogrammetry and 3D laser scans
The result of a 3D survey of a castle with a drone using photogrammetry and 3D laser scans is a point cloud. Depending on the requirements, 2D as-built plans, sections, views and façade drawings can be created from the point cloud. Orthomosaic photos of conditions can also be derived from the detailed scan data and high-resolution images in a wide variety of scales and resolutions for visual documentation, inspection and damage mapping. Furthermore, 3D CAD models and photorealistic 3D mesh models can also be created.
Accuracy and resolution of a 3D survey of castles with a drone and 3D laser scans
The accuracy at a single location differs from the accuracy over the entire object. The accuracy at a single location of the laser scanner is ± 2 mm. Below 10 m distance to the object, a relative accuracy of 1 mm can be achieved.
In the case of photogrammetric scanning with a drone or terrestrial photogrammetry, accuracy depends on the ground resolution, which is determined by the camera sensor size, the lens and the distance to the object or the flying height. Accuracy is within a range of 1–2 times the ground resolution in an x/y direction. The deviation in height (z) is usually slightly higher (max. 3 times the GSD).
We generally hand over the measurement results of castles and castle complexes with georeferencing in the coordinate system required. Georeferencing is performed using available fixed points or ground control points, which are measured using a GPS or a tachymeter. The ground control points are also used for stabilising and referencing the photogrammetry. 3D laser scans can also be used for referencing. Photogrammetric image processing is then performed simultaneously with the recorded laser scans. Based on an accompanying survey of ground control points using a tachymeter, accuracies of ± 1 cm can be achieved on the entire object in this way.
Below an example using our 42-megapixel full-format camera of a drone with a 35-mm lens:
Ground resolution (GSD = Ground Sampling Distance) at a 10-m distance from the lens / flying height above the object: 0.15 cm. This results in a relative accuracy of 0.15–0.3 cm when the ground control points are of a good quality.
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