## 4 Results and Discussion
### Height Estimation of Single Objects
#### 4.4.2 Trees  
Trees were investigated in two separate classes: deciduous trees, located especially on roadsides, parks and cities, and coniferous trees, found in forested areas and forest patches. Only single, isolated trees, not close to buildings or any other objects, were taken into consideration. In this case, the visible crown diameter was used as the geometric parameter. One hundred trees were investigated, and the same formula for height percentage computation, Equation (4), was applied. Based on diameter, they were grouped into seven different categories, each containing approximately 12 trees. The mean reconstruction percentages gradually increase with crown diameter and the standard deviations decrease (Figure 6). For WorldView-3, the heights of coniferous trees with crown diameters <2.5 m (8 pixels in image space) are reconstructed less than 50%, whereas trees with crown diameters larger than 5 m (16 pixels in image space) are over 95%. Generally, heights of coniferous trees are better estimated from WorldView-3 than from the Pleiades DSMs, where trees with diameters >7.5 m (11 pixels) barely reach 75% height reconstruction. For deciduous trees (Figure 6b) it can be observed that the situation is reversed: they get better height information from Pleiades DSM, than from WorldView-3 DSM. This is mainly because of the different acquisition times, June for Pleiades and April for WorldView-3, indicating leaf-on and leaf-off conditions which clearly influence the appearance and texture of the trees in the images. For the deciduous trees, only the stems and branches are visible in the WorldView-3 images, resulting in a poor dense image matching quality. For trees with a crown diameter larger than 9 m, heights of just over 50% of the tree values are reconstructed. When analyzing the two tree types only from the Pleiades images (Figure 6), we could see that there is a slightly better height reconstruction for the very small and large deciduous trees, compared with the coniferous. The small deciduous trees in the first group (with crown diameters smaller than 2.5 m) have 26% of their real height reconstructed, whereas the small coniferous trees in the first group have only 21%. The same is true for the last group, where large deciduous trees (with crown diameters bigger than 8.75 m) have percentages close to 80%, whereas for coniferous they reach only 75%. On the other hand, for the coniferous trees of medium sizes (with crown diameters between 2.5 and 7.5 m) we obtained better height reconstruction percentages than for the deciduous. Figure 5: Interval-based percentage and standard deviation for height estimation of vehicles depending on (**a**) lengths and (**b**) widths. Two examples of height estimation of a coniferous (Figure 7) and a deciduous tree (Figure 8) are shown. They were comparatively analyzed for Pleiades and WorldView-3 satellite images based on both DSM and point cloud. For single coniferous trees with a 7 m crown diameter (Figure 7) we achieved different results based on the input data. From the true height of 12.2 m, the estimation resulted in approximately 12 m for WorldView-3 and only 8 m for Pleiades, which represents 98% and 65% of the real height. A small area of the DSMs and the 3D point clouds generated from the Pleiades and WorldView-3 satellite imagery are shown in Figure 8. The largest deciduous tree with leaves (Figure 8a first row) has a reasonable appearance in the DSM and an estimated height of 14 m. Meanwhile, the same leafless tree in the WorldView-3 image (Figure 8a second row) has a height of only approximately 4 m. A visual analysis of height differences for this deciduous tree and a small building (next to the tree) is shown in two profiles (c) and (d) in Figure 8.  
Figure 6: Interval-based percentage and standard deviation for height estimation of single trees (**a**) coniferous trees and (**b**) deciduous trees.