7. Representation of (a) 3D matrix of voxels, and (b) voxelization of point cloud data within a voxel with different statistical procedures. dimensions were tested: 0.25, 0.35, 0.45, 0.55, 0.65, 0.75, 0.85, 0.95, 1.05, 1.15, 1.25, 1.35, 1.45 and 1.55 m. The minimum voxel size was equal to the footprint size. The voxel size in Z dimension was not modified, and the vertical distance between waveform bins, based on the temporal sample spacing of the ALS system, was respected. Therefore, the voxel size in Z dimension was 0.3 m, calculated from the temporal sample spacing (see Equation 5). In addition, the voxel value was computed using five different statistics (maximum, mean, median, percentiles 90 and 95) for all the waveform bins within each voxel. In the analysis of side-lap effect on the estimate of forest attributes, three voxel sizes were tested: 0.25, 0.5 and 1 m. As in the first analysis, Z dimension of voxels was calculated from the temporal sample spacing (i.e., 0.3 m) (see Equation 5). However, only maximum as the assignation value was tested for this second analysis to keep the significance of the maximum amplitudes from the original waveforms when generating the pseudo-vertical waveforms (Hermosilla et al., 2014b).