# Geometric Characterization of Vines from 3D Point Clouds Obtained with Laser Scanner Systems
## 4 Discussion  
It should be noted that the technical limitations of each piece of equipment have guided this work in its two subobjectives: to test the possibility of calculating the volume occupied by the trunks of vines in a vineyard using clouds from points taken with TLS equipment, and to extrapolate the best possibility to a real case study scanned with MMS, where it would be feasible to elaborate a vine size map based on the volume of each vine. Firstly, the TLS point clouds have digitalized, with high detail and precision, the areas of the vines that were within their reach. Nevertheless, the areas occluded behind the equipment itself or its intermediate elements were not captured, thus making the three-dimensional definition of the scanned object incomplete (in this case, the vines of the vineyard), similar to the problems found in [61]. Secondly, the mobile capture system of the MMS solves this deficiency, as the number of views taken of the object covers most of its faces. This result could be achieved by increasing the number of TLS scan stations, but, considering the large number of faces these objects have, this process would be too costly for the intended purpose. However, the point density and low-quality cause other problems (also treated in [21]). Thus, the approach to treat and evaluate the obtained data should be different. In fact, the different algorithms implemented obtained different results depending on the scanning systems utilized because of the differences in the types of information acquired. Taking advantage of the TLS (detail and precision) and considering their limitations (occlusions), the two proposed algorithms (OctoMap and CHC) can estimate the volume occupied by the scanned vines with the proposed methodology. OctoMap does not need to know the entire figure if the occlusions are smaller than the calculated voxel size [50], which makes this method appropriate for TLS, where many faces of the object are occluded. Indeed, we identified a defect error in the results due to the occlusion of the lower face of the arms, which could be solved by placing the scan stations at a lower height from the ground. The CHC algorithm is not as strongly affected by this lack of scanned faces since in the case of figures with simple geometries, such as cylinders, the closing of the convex envelopes of the point groupings obtained by this algorithm is accurate and resolves the occlusions suffered by the cloud. Nevertheless, the capture performance of the TLS makes it unfeasible to survey large extensions of land, such as those covered by agricultural crops. However, the application of the tested algorithms to MMS point clouds is not possible because they have lost the precision and definition conditions required by OctoMap and CHC. In addition, those two algorithms also resulted in lower accuracy in the determination of the VSAO volume for TLS. Thus, it can be concluded that OctoMap and CHC are not the most appropriate algorithms for this case study. We recommend increasing future efforts in developing strategies for the skeleton algorithm. The proposed change of strategy that focuses on modelling algorithms based on the internal structure of the objects (L\({}_{1}\)-medial skeleton [52]), and not on determining the closure of their surfaces (OctoMap [50] and CHC [51]), has made it possible to estimate the volumes of individualized vines scanned with MMS point clouds, as the results show. Even the estimation of volume with this strategy improves, in some cases, the values obtained with TLS clouds (3.55% and 2.46% errors for the VCTS segment mean and line string mean, respectively, compared with a 6.40% error with the CHC algorithm and TLS point clouds). However, in the case of a TLS in which two faces of the trunk are perfectly defined but there are many occlusions because of the lack of perspective, the skeleton algorithm returned many errors that require further development to be robust and usable.