Peer Reviewed Articles
249 Testing Camera Calibration with Constraints
Huang Youcai and Robert M. Haralick
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Known geometric relationships between points, lines, and
planes on a three-dimensional (3D) object can be used as
constraints in the camera calibration process to improve the
accuracy of estimates. Ten constraints have been constructed
and tested numerically. The accuracy improvement has been
evaluated theoretically and empirically by comparing the
variances and traces of the covariance matrix of the 3D
points obtained from the camera calibration without constraints
with those derived from the process with constraints.
It is not uncommon to observe an order of magnitude improvement
in the variances of the estimates for problems
having multiple constraints. Statistical tests comparing the
theoretical prediction with the empirical observed data validate
the approach.
259 Parallel Image Processing Applied to Radar Shape-from-Shading
A. Goller, M. Gelautz, and F. Leberl
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Various widely used radar image processing algorithms require
considerable computing resources but can take advantage
of a parallel implementation. We focus on the shape-from-shading (sfs) algorithm in its application to radar
images. A given serial version of the sfs algorithm was parallelized and improved to handle large images. We experimented
with parallelization techniques such as data decomposition,
the manager/worker method, and dynamic load
balancing with double buffering. The parallel version of sfs
was ported to two supercomputers: Meiko's CS-2HA and Intel's
PARAGON XP/S-A4 distributed memory machines, and to
a cluster of workstations (CoW) made up of Silicon Graphics'
Indies. Important results concerning the performance of the
parallel sfs implementation with those architectures are presented
and compared to each other, showing that 14 processors
can speed up sfs by up to 13 times over the use of a
single processor.
269 The Analog-to-Digital Transition and Implications for
Operational Use of Airborne Videography
Jung-Sup Um and Robert Wright
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Recent advances in domestic consumer video technology and
improvements in computing power indicate possibilities for
overcoming the limitations of analog video. This has prompted
a re-evaluation of the potential of airborne video as an operational
digital remote sensing tool. First, in retrospect, the
difficulties of applying digital analysis to video are explained,
based an four major links for image quality degradation.
To exemplify the importance of technological
advance in improving analog video digitization. a comparison
is made of synchronization fidelity between older and
newer model frame-grabbers. Recent developments in custom-built digital video cameras and video are explained,
to highlight the important technological advance of "off-the-shelf" digital video. Finally, the "digital revolution"' from the
commercial video and computer markets is discussed in
terms of the significance for the practicality of digital video
remote sensing. In conclusion, from the perspective of past
limitations, it is asserted that the "digital revolution " will
lead to significant benefits for routine use of operational digital
video remote sensing.
277 Virtual Reality Applied to User Interfaces for Digital
Photogrammetric Workstations
Michel Boulianne and Clément Nolette
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The use of an all-photogrammetric mouse as an alternative
to other input devices for softcopy photogrammetric systems
is proposed. With this interface. the operator's hand movements
are linked to the floating mark by means of a realtime
hand monitoring system. Two cameras positioned underneath
the operator's hand locate and track one or more
light spots attached to the hand. Through a feedback loop,
the user has the feeling of directly manipulating the floating
mark by hand in the stereomodel, Besides being more intuitive
than the existing interfaces, the proposed one offers the
possibility to measure distances as well as terrain facets in
only one operation. Time savings of up to 45 percent are
reported for DEM collection.
281 An Innovative Approach Using Digital Photogrammetry to
Map Geology in the Porcupine Hills, Southern Alberta, Canada
Daniel Lebel and Ronald Da Roza
Abstract
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Digital and analog air photographs and field observations
have been used to map resistant sandstones within the Porcupine
Hills Formation in southern Alberta. The traces of
these beds were plotted in three dimensions using a digital
stereoplotter. The procedure permits corrections of plotting errors
made by the geologist who could previously use only a
few ground points recognizable in the field to locate sandstone
beds on the digital topographic base map. Digital orthophotos
and elevation data were then used to calculate
three-point solutions of the strike and dip of sandstone
ridges. These procedures allowed the geologist to improve his
geological interpretation and to validate the digital transfer
of line work by the photogrammetrist. Photogrammetrically
calculated bedding measurements augmented those measured
in the field and allowed the geologist to delineate several
previously unrecognized folds.
289 Contour Line "Ghosts" in USGS Level 2 DEMs
Peter L. Guth
Abstract
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Characteristics of digital elevation models (DEMs) differentiate
those produced from digitized contour lines from those
produced directly from imagery. Contour-to-grid algorithms
produce more grid-node elevations with the same elevation
as the contour lines compared to elevations different from
contour line elevation; this "ghost" artifact reflects the DEM
generation process and not the underlying topography. The
effect ranges from extreme to slight. In new USGS Level 2
DEMs, elevations corresponding to the source map contours
can occur twice as often as similar elevations between contour
lines, and overall contour line elevations are over represented
by about 30 percent, Three independent techniques
demonstrate the contour line ghosts: visual examination of
elevation histograms, the power spectrum from a fast Fourier
transform of the elevation distribution, and direct computation
of a contour ghost ratio. These artifacts do not diminish
the significant improvement of the Level 2 DEMs over Level 1
products, but require users to carefully evaluate their data
and analysis methodology, especially when computing derived
surfaces from the DEM which magnify data irregularities.
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