46
4 An Innovative Measurement Instrument …
benefit most from the strengths of this technology (Du and Teng 2007; Abellán et al.
2006). Nevertheless, while a terrestrial laser scanner was used to quantify rills on
an angle of repose slope, an even greater density of points was needed to capture
sufficient rill morphology (Scherer and Lerma 2009; Hancock et al. 2008). Moreover,
it is very difficult to monitor the time-variable process of an individual mass failure
with these techniques because of the randomness and suddenness of such an event.
Photography was invented in 1839 by a Frenchman, Louis Daguerre, and a year
later terrestrial photos were first used for surveying (Wolf 2002). Compared to terrestrial laser scanning, the philosophy of terrestrial photos captured the geometry and
visualized it simultaneously; the coordinates of relevant object-describing points
were determined by the intersection of an image ray and the predefined primitive
(Scherer and Lerma 2009; Ohnishi et al. 2006). Digital photogrammetry was applied
for measuring erosion rates on complex-shaped soil surfaces under laboratory rainfall conditions (Rieke-Zapp and Nearing 2005). However, the images of the object
taken with a camera had to be geo-referenced as a preparatory step, and an intelligent tacheometry was used for online and on-site measurements (Scherer and Lerma
2009; Rieke-Zapp and Nearing 2005). Structured-light 3D surface imaging techniques were used to compute the 3D model of a face by projecting a simple colored
stripe pattern onto the face, and the depth information was then calculated by considering the distortion of the stripes in the face caused by its shape (Geng 2011; Wang
et al. 2010; Fechteler and Eisert 2009; Peng 2007; Zhang 2005). If the target was
moving, single-shot techniques had to be used to acquire an instant snapshot 3D surface image of the 3D object at a particular time. Nevertheless, to our knowledge, no
such techniques have been applied to the 3D object in dynamic motion in literature
before.
Recently, a structured-light 3D surface-measuring instrument, the MX-2010-G
topography meter, was designed and manufactured to observe the slope behavior
under rainfall simulation. Evaluation tests showed that the errors among the volumes
observed by the topography meter and those of the conventional instruments were
within 10% (Xu et al. 2015). However, the above-mentioned paper was focused on
data processing and calibration testing. It did not give detailed information on the
structure of the 3D surface measuring instrument. In addition, the definition of laser
lines recorded by the camera had a high requirement for the ambient light. If the
ambient lighting was sufficiently strong, the contrast of the laser footprints would
decrease on the sloping terrain, and the image would become vague. Whether it is
possible to use the topography meter for conducting site-specific surveys of landslides
has become an urgent question to be resolved.
Gravity erosions, the mass failures on steep slopes that are triggered by selfweight, contrast with other soil erosions requiring physical impetus of wind or
water, and were among the most important natural hazards in mountainous regions
(Hergarten 2012; Gokceoglu and Sezer 2009). Gravity erosion tends to happen as an
episodic event in which large sections of the steep slope fail. However, to monitor
the time-variable process of an individual mass failure is very difficult because of
the randomness and suddenness of such an event. It is rather difficult to conduct a
field survey of soil and water conservation on the Loess Plateau of China. During
the natural rainfall events, the site-specific observation of gravity erosion is almost
4 An Innovative Measurement Instrument …
benefit most from the strengths of this technology (Du and Teng 2007; Abellán et al.
2006). Nevertheless, while a terrestrial laser scanner was used to quantify rills on
an angle of repose slope, an even greater density of points was needed to capture
sufficient rill morphology (Scherer and Lerma 2009; Hancock et al. 2008). Moreover,
it is very difficult to monitor the time-variable process of an individual mass failure
with these techniques because of the randomness and suddenness of such an event.
Photography was invented in 1839 by a Frenchman, Louis Daguerre, and a year
later terrestrial photos were first used for surveying (Wolf 2002). Compared to terrestrial laser scanning, the philosophy of terrestrial photos captured the geometry and
visualized it simultaneously; the coordinates of relevant object-describing points
were determined by the intersection of an image ray and the predefined primitive
(Scherer and Lerma 2009; Ohnishi et al. 2006). Digital photogrammetry was applied
for measuring erosion rates on complex-shaped soil surfaces under laboratory rainfall conditions (Rieke-Zapp and Nearing 2005). However, the images of the object
taken with a camera had to be geo-referenced as a preparatory step, and an intelligent tacheometry was used for online and on-site measurements (Scherer and Lerma
2009; Rieke-Zapp and Nearing 2005). Structured-light 3D surface imaging techniques were used to compute the 3D model of a face by projecting a simple colored
stripe pattern onto the face, and the depth information was then calculated by considering the distortion of the stripes in the face caused by its shape (Geng 2011; Wang
et al. 2010; Fechteler and Eisert 2009; Peng 2007; Zhang 2005). If the target was
moving, single-shot techniques had to be used to acquire an instant snapshot 3D surface image of the 3D object at a particular time. Nevertheless, to our knowledge, no
such techniques have been applied to the 3D object in dynamic motion in literature
before.
Recently, a structured-light 3D surface-measuring instrument, the MX-2010-G
topography meter, was designed and manufactured to observe the slope behavior
under rainfall simulation. Evaluation tests showed that the errors among the volumes
observed by the topography meter and those of the conventional instruments were
within 10% (Xu et al. 2015). However, the above-mentioned paper was focused on
data processing and calibration testing. It did not give detailed information on the
structure of the 3D surface measuring instrument. In addition, the definition of laser
lines recorded by the camera had a high requirement for the ambient light. If the
ambient lighting was sufficiently strong, the contrast of the laser footprints would
decrease on the sloping terrain, and the image would become vague. Whether it is
possible to use the topography meter for conducting site-specific surveys of landslides
has become an urgent question to be resolved.
Gravity erosions, the mass failures on steep slopes that are triggered by selfweight, contrast with other soil erosions requiring physical impetus of wind or
water, and were among the most important natural hazards in mountainous regions
(Hergarten 2012; Gokceoglu and Sezer 2009). Gravity erosion tends to happen as an
episodic event in which large sections of the steep slope fail. However, to monitor
the time-variable process of an individual mass failure is very difficult because of
the randomness and suddenness of such an event. It is rather difficult to conduct a
field survey of soil and water conservation on the Loess Plateau of China. During
the natural rainfall events, the site-specific observation of gravity erosion is almost