ИСТИНА

We compared ground photogrammetry surveys of the same forest stand using three different cameras and four methods: time-lapse fisheye and time-lapse panoramic survey with Garmin Virb camera, time-lapse survey with a GoPro camera and a survey with Nikon camera with a distance gap. The best the point cloud for the extraction of stems and the characteristics of tree stems and ground layers have been obtained with Nikon camera. This method allows us get the cloud with smallest noise using the survey from the perimeter. The second best was Garmin camera with panoramic images. The point cloud needs to be cleaned from noise significantly and only in manual mode. GoPro camera showed the worst result – only some photos were available for processing. The survey is carried out in “forward” mode and it results in the change of the distance between the camera and the vegetation objects. It leads to the issues in detecting tie points between different photos. For all cameras, we get the best result while processing a small number of pictures (3-10) Advantages of photogrammetric survey: it is fast, not overloaded with detail, has a relatively big territory of survey (compared to LiDAR), clearly distinguishes the ground level, and RGB colors improve visual interpretation. Ground photogrammetry also has its disadvantages: distortions and noise increase with the height of vegetation; it is hard to take into account different geometry of vegetation items in the sets of images, resulting in complicated processing; it is hard to detect small branches.