Following equipment installation, horizontal and vertical coordinates of the
camera locations and ground control points (GCPs) are surveyed with a total
survey station. GCPs are landmarks observed in a camera view that have known
object space and image space coordinates. For the series of physical model
experiments conducted, GCPs consisted of tick marks painted on the varying
bathymetry of the model. Figure 22 shows example GCPs for the Structure 3 and
4 experiments. Survey data, lens distortion corrections, image digitizer
information, and a video snapshot of the drained physical model determined
geometry solutions for each camera view. A geometry solution can be
determined for each camera view with as few as two GCPs. However, more
GCPs allow for a least-squares solution with minimal error. For each physical
model configuration (i.e., Structures 1 through 4), cameras were reoriented to
provide a field of view of the desired measurement area. A geometry solution
was calculated for each camera orientation and stored in a database for access by
the image processor and coordinate transformation algorithms. Structures 3 and
4 had the same camera orientation, eliminating recalculation of camera geometry.
Figure 22. Structures 3 and 4 C1 camera view. GCP locations used for view
geometry solution are circled
Diffuse incandescent lamps are positioned to illuminate the waves over an
area of interest on the free surface in a manner to create a clearly visible
signature of the wave field by the camera. Care is taken to prepare the area
around and above the physical model to minimize undesired shadows and
illumination within the field of view. During the testing phase of CIIS
development, it was observed that the model illumination was refracted through
the water column onto the model bathymetry. The refracted high-intensity bands
dominated the video signal and degraded the phase structure of the observed
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Chapter 5 Video-Based Wave Direction Measurement
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