**5. Discussion**

The experimental results and analysis of the two Lidar types of Hesai Pandar64 and Ouster OS-1-64 are shown in Sections 4.1 and 4.2, respectively. The results are based on a 3D simulation scanning applied at different angular orientations (30◦ to 50◦ ) for both types. The produced point clouds are analyzed in terms of density of points pts/m<sup>2</sup> , coverage, and accuracy.

Every Lidar type showed its own advantages and the performance was found to be comparable. The performance evaluation is based on the three mentioned parameters of density, coverage, and accuracy, and they are prioritized as follows:


Based on the results achieved as shown in Section 4, we can observe the following:


Accordingly, it was found that the ideal recommended angle for an MMS using a single Hesai Pandar64 Lidar is 45◦ (Figure 26), since it will ensure: (1) high coverage of the surrounding features, (2) high density for the ground features, and (3) a relative accuracy of ≤10 cm for 95% of the scanned data.

On the other hand, the ideal recommended angle for an MMS using Ouster OS-1-64 Lidar is 35◦ (Figure 26), since it will ensure: (1) high coverage of the surrounding features, (2) high density for both ground and off-ground features, and (3) a relative accuracy of ≤10 cm for 95% of the scanned data.

data.

in Figures 18 and 24.

and 25.

Every Lidar type showed its own advantages and the performance was found to be comparable. The performance evaluation is based on the three mentioned parameters of density, coverage, and

• Density criterion: since most of the mobile mapping applications are aimed for road asset inventory tenders, the higher density magnitude on the ground surface was preferred. • Coverage criterion: with the variety of feature classes off the ground like traffic signs, trees, vehicles, people, buildings, etc. It was important to have a relatively high coverage off the

• Accuracy criterion: accuracy is preferred to be as high as possible if it does not conflict with the

• For both Lidar types, the tilting angle increase was proportional to the achieved density of points on the ground surface, as shown in Figures 13 and 20, while it was inversely proportional to the achieved density of points on the off-ground features such as the road sign shown in Figures 19

• For both Lidar types, the tilting angle at 30° was efficient for running the detection and fitting of

• The achieved point clouds accuracy of the scanned objects was proportional to the increase of the Lidar tilting angle. However, this was negatively affecting the coverage attained on the lower parts of the building facades facing the trajectory as shown in Figures 17a,b and 23a,b. On the other hand, larger tilting angle negatively affected the coverage attained on the higher parts of

• The impact of the beams distribution on the coverage performance is shown in Figures 17 and 23. The upper parts of the building aside façade slice (Figure 11) is fairly scanned using OS-1-64 at every tilting angle while not fully scanned at lower tilting angles using Pandar64. This is related to the fact that Pandar64 laser beams are concentrated at the horizontal plane and then

• Furthermore, the accuracy improvement while increasing the Lidar tilting angle was related to the increase in the incidence angle of the scanning beams when hitting the objects as illustrated

Accordingly, it was found that the ideal recommended angle for an MMS using a single Hesai Pandar64 Lidar is 45° (Figure 26), since it will ensure: (1) high coverage of the surrounding features, (2) high density for the ground features, and (3) a relative accuracy of ≤10 cm for 95% of the scanned

On the other hand, the ideal recommended angle for an MMS using Ouster OS-1-64 Lidar is 35° (Figure 26), since it will ensure: (1) high coverage of the surrounding features, (2) high density for both ground and off-ground features, and (3) a relative accuracy of ≤10 cm for 95% of the scanned

Based on the results achieved as shown in Section 4, we can observe the following:

a cylindrical object shape of a road sign legs, as shown in Figures 19 and 25.

the building facades aside the trajectory as shown in Figures 17c,d and 23c,d.

larger tilting angles are required to cover the facades higher parts.

accuracy, and they are prioritized as follows:

ground in a mobile mapping project.

above two criteria or when comply with one of them.

**Figure 26.** Ideal angular orientation of the selected Lidar devices. (**left**) Pandar64. (**right**) Ouster OS-**Figure 26.** Ideal angular orientation of the selected Lidar devices. (**left**) Pandar64. (**right**) Ouster OS-1-64.

#### 1-64. **6. Conclusions**

**6. Conclusions** In this paper, two state-of-the-art multi-beam spinning Lidar types were investigated, namely, Ouster OS-1-64 and Hesai Pandar64. The investigations assumed a mobile mapping system equipped with a single multi beam Lidar. A 3D simulated urban scene scanning was applied at a constant driving speed of 36 km/h and at different angular orientations (30◦–50◦ ) for both Lidar types. The produced point clouds of ground and off ground features were analyzed in terms of density of points pts/m<sup>2</sup> , coverage, and accuracy. Based on the extensive analysis applied for both Lidar outputs, it was found that the ideal angular orientation of the Ouster OS-1-64 Lidar type is 35◦ , while the ideal angular orientation of the Hesai Pandar64 is 45◦ , as illustrated in Figure 26. These orientation angles are recommended mainly for mobile mapping applications where the major customers demand is for engineering surveys, asset management inventory, roadway condition assessment, power lines clearance, 3D designs, as built surveys, cultural heritage documentation, and other geospatial applications.

It is worth to mention that the applied simulations did not consider a non-uniform vehicle speed, which is expected to have an impact on the results. Furthermore, the study did not account for different mapping scenarios in the simulated 3D model, which would likely strengthen the conclusions made in this paper.

Future work can be applied to investigate other newly released Lidar types including the solid state Lidars. Moreover, dual Lidar installation can also be investigated.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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