“Bare earth” structure-from-motion data: Evaluating color-based point
classification and fine-scale topography
Abstract
Classification of ground points is a critical step in producing digital
elevation models of the Earth’s surface for studying landscape processes
and geomorphic or ecological change. This paper describes a new
algorithm for ground point classification and assesses the relative
accuracy of the resulting ground surface in filtered light detection and
ranging (lidar) and structure-from-motion (SFM) datasets. This
color-enhanced multiscale curvature classification algorithm (MCCRGB)
extends a popular lidar classification method (MCC) by introducing
classification updates that distinguish vegetation and ground points by
color. Multispectral lidar and SFM data imaging a subalpine volcanic
tree kill are used to evaluate both methods. We find that color-based
classification updates remove tree fall, low canopy, and brush, often
requiring fewer iterations on large, ultra-high-density datasets. SFM
data capture rills, small channels, and tree fall not visible in the
lidar data. “Bare-earth” datasets from each method are internally
consistent (mean vertical differences: -0.01 to 0.08 m) and validation
at a set of 165 checkpoints shows a mean vertical difference of 0.46 m
(standard deviation: 2.21 m) with the SFM ground points. The methods
produce consistent topographic derivatives from each data source,
including digital elevation models, slope, and profile curvature. While
SFM derivatives are more variable and less continuous, the filtered
products may be useful for geomorphic mapping and analysis, including
mapping of microtopography or measuring landscape change in challenging,
forested settings.