In most structural geology and neotectonic applications, we are
interested in a bare surface model. In areas of light to dense
vegetation, this preference for bare surfaces becomes the primary
disadvantage to photo-based 3D reconstruction relative to active
source 3D data collection tools. LiDAR collects a 3D point location
with a single pulse of light, thus is capable of collecting ground
surface points wherever the pulse of light is able to penetrate the
vegetation, reflect off the ground surface, and return to the instrument.
The requirement in photo-based 3D reconstructions for
multiple images collected from different perspectives for 3D point
geometry reconstruction dramatically reduces the number of
resolvable ground surface points due to the occlusion of the ground
surface by vegetation when moving from one camera position to
the next. However, because the SfM process creates a point cloud,
as long as the vegetation is sparse enough to allow a sufficient
number of ground features to be identified and matched, some of
the approaches developed for classification of LiDAR data can be
applied to SfM-derived point clouds. Furthermore, one of the
popular commercial photo-based 3D reconstruction packages
(Table 1), Agisoft PhotoScan, has implemented a point cloud classification
scheme for classification of ground surface points and
vegetation (http://www.agisoft.ru/tutorials/photoscan/08).