To determine potentially dangerous trees in the proximity of the transport infrastructure, it was first necessary to obtain data from the field to create algorithms and verify their functionality. Trees that could endanger traffic participants by their fall are determined by their height and distance from the given infrastructure. To determine the heights of trees, it is necessary to know the altitude of the area, which is expressed by a digital terrain model (DTM). The terrain is a representation of the earth's surface in digital form without natural or artificial objects and for the area of interest is shown below.
In contrast, a digital surface model captures all objects on the surface. The model was created using the photogrammetric method Structure from Motion from a raid by a drone. The raid took place on 8 August 2019 at a height of 130 m and with an overlap of images of 80 % near the National nature reserve Rejviz in the Jeseníky Protected Landscape Area. The subject of the raid was a paved asphalt road and the surrounding vegetation, which in some places turns into clearings.
The output of the raid in the Rejviz locality are photographs capturing the area of interest, from which a point cloud containing 1,309,707 points was subsequently generated. By converting the point cloud to a raster format, the necessary digital model showing altitudes was created.
The height of the trees and all objects itself was determined from the difference between the altitude of the surface model and the terrain model. The following normalized digital surface model (nDSM), therefore, shows the required heights.
