**4. Image Classification Results**

According to the set of classification feature parameters listed in Table 2, an image classification based on C5.0 was performed. A quantitative evaluation of the classification results is shown in Table 4. The overall classification accuracy based on BRDF\_0◦ (63.9%) was approximately 24% higher than that based on the DOM. Two principal plane reflectance feature sets (BRDF\_PP+CP) were used for the fine classification of vegetation, and the best results were obtained. The overall accuracy of classification (89%) was greatly improved by 39%, and the kappa coefficient (0.870) was increased by 0.438. The classification results for the study area based on BRDF\_PP+CP are shown in Figure 6.



**Figure 6.** Classification results: (**a**) the reference map, (**b**) the map produced using DOM, and (**c**) the map produced based on multi-angle reflectance characteristics of the observed principal planes and cross-principal planes.

From Figure 6, the object-oriented vegetation classification method based on the multi-angle reflectance characteristics achieved good mapping results with clear boundaries and an accurate location distribution. BRDF\_PP+CP feature sets helped to improve the recognition accuracy of the junction of different tree species, as shown in the blue rectangle in Figure 6. This was because the observation data from different angles could reflect the difference in tree structure, and the tree species could be identified well using multi-angle difference features. In addition, it could improve the accuracy of the division of corn and field roads, as shown in the yellow rectangle in Figure 6. However, although the BRDF\_PP+CP greatly improved the identification accuracy for shadows, it performed poorly regarding the distinction between shadows and weeds with a low height, as shown in the black area of Figure 6. The spectral vegetation types under shadow coverage in the study area were various, and the spectral characteristics of shadow were similar to those of weeds with a low height.
