## 4 3D Laser Terrestrial Scanning: Knowledge Base
### Terrestrial Laser Scanning: Realization Phase  
To create 2D project documentation, it is necessary to set two important parameters, resolution and quality. These two parameters are the most important for the whole process, because they affect the level of detail captured and the time required to obtain data from one scanner position, which is adequately reflected in the total time required to obtain all data and help in the correct process of registering individual scans in postprocessing. The first parameter, resolution, determines the point distance, which then determines the level of detail. By increasing this parameter, we will achieve the capture of a larger number of points and, at the same time, reduce their distance. Otherwise, lowering this parameter results in a smaller number of points being captured while increasing the distance between them. For our purposes, based on the required level of detail and time saving in calculating the available distance to the object of interest, a resolution of 1/4 was chosen. This represented the distance of the point 6.136 mm at 10 m from the scanner. The quality setting primarily determines the measurement speed and 'noise' reduction level, i.e., increased quality value increases the measurement time that the scanner spends on each scan point, while performing multiple measurements to confirm the information and then averaging the result. In addition to the above, this parameter also uses a noise reduction algorithm that determines whether the differences in the scan points are an accurate representation of detail or noise. The algorithm compares the scanned points at a certain distance to each other and determines whether their difference is in the tolerance specified by the quality setting. If not, the scan point is removed, resulting in noise reduction. The setting of this parameter also largely depends on the scanning conditions, such as interior or exterior spaces, weather conditions, etc. To meet the condition of saving time, we tried to achieve optimal conditions and thus achieve the quality setting parameter--\(2\times\). Based on preliminary on-site measurements, it was necessary to determine the distance between the scanner positions and the distance of the reference points from the scanner position. Table 2 shows a comparison of the settings of various parameters (quality and resolution) and the resulting achieved number of scan points on reference objects (spheres) at a given setting. Green values represent higher accuracy, yellow values represent lower accuracy and gray values represent low (<20) or insufficient number of acquired scan points required in the registration process. The minimum value for achieving green values is 80 captured scan points. The following columns represent the average time required to record data from a single scan position when scanning with RGB and when scanning without RGB. Each area of scenery that was scanned (see Table 1) required specific settings depending on the conditions. When scanning exterior scenery, it is always necessary to consider weather conditions at a given time. These measurements also show that in ideal weather it is sufficient to use the quality setting \(2\times\) at a resolution 1/4 and the location of reference points and targets at a distance up to 10 m.  
Scanning was performed in November 2019 with the terrestrial laser scanner Faro Focus X 330, with the possibility of scanning to a distance of 330 m and accuracy of 2 mm. To achieve the highest possible accuracy, a combination of 140 mm reference balls (spheres) and targets (checkboards) was used. When using this type of terrestrial laser scanner, it is possible to scan without the use of reference spheres and targets, which can ultimately save time and money, but at the expense of scanning accuracy of the object.