Peer-Reviewed Articles
1145 The Sign Permutation in the Rotation Matrix and the Formulation
of the Collinearity and Coplanarity Equations
Tian-Yuan Shih
Abstract
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Two basic variations arise in the formulation of the collinearity
and coplanarity equations. These two variations are generally referred to as
the
diapositive
equation and the negative equation. The relationship between these two formulations
and the rotation matrices is investigated in this study. This study has revealed
that the sign changes of principal distance in both the collinearity and coplanarity
equations are coupled with the sign permutation of the elements in a rotation
matrix.
1151 Using Theoretical Intensity Values as Unknowns in Multiple-Patch Least-Squares
Matching
Amnon Krupnik
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Least-Squares Matching (LSM) has become a common technique for obtaining accurate
location of corresponding points. On several occasions, the basic model was
generalized to handle more than two image patches by introducing unknown theoretical
intensity values into the mathematical model. With these additional unknowns,
gray values rather than gray-value differences are used as observations. Two
aspects of introducing such unknowns are discussed. The first aspect is the
equivalence of the generalized model to the basic one. The second aspect is
the efficiency of the solution. Experimental results are presented and discussed.
1157 A Fast Solution to Local Viewshed Computation Using Grid-Based
Digital Elevation Models
Jianjun Wang, Gary J. Robinson, and Kevin White
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A new algorithm for generating viewsheds from grid-based digital elevation
models is presented. It uses a combination of sightline analysis and the relationships
between the local surfaces at the source and destination points. Depending
on the nature of the terrain surface, significant savings in computation time
over existing sightline only based algorithms are made because a substantial
proportion of the destination points can be determined as invisible from the
source point without the need for sightlines. The new algorithm also produces
more reliable results by better consideration of points at or near the viewshed
horizon.
1165 Comparison of Derivative Topographic Surfaces of a DEM Generated
from Stereoscopic SPOT Images with Field Measurements
Philip T. Giles and Steven E. Franklin
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A digital elevation model (DEM) derived from SPOT satellite imagery is evaluated
for accuracy in elevation and three of its derivative topographic surfaces:
slope gradient, incidence value, and profile curvature. The raw DEM surface
is observed to contain a systematic pattern of noise, and analysis of semivariance
is used to determine an appropriate window size for filtering. Field measurements
of slope gradient, incidence value, and profile curvature are used to evaluate
the accuracy of the derivative surfaces. Several processing options are employed
to maximize the correlation between the surface representations and the field
data. Results emphasize the caution that must be used before using the digital
elevation model and its derivative topographic surfaces as estimates of the
true landscape configuration.
1173 Geometric Correction of SPOT and Landsat Imagery: A Comparison
of Map- and GPS-Derived Control Points
N.G. Kardoulas, A.C. Bird, and A.I. Lawan
Abstract
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The geometric correction of Landsat MSS (80-metre pixel), Landsat TM (30-metre
pixel), and SPOT Panchromatic (10-metre pixel) satellite images was investigated
using 1:100 000-scale topographic maps and GPS data in an area of Nigeria.
The geometric corrections with first-degree polynomials, using either GPS-
derived points or 1:100 000-scale topographic map derived points, yielded RMS
error values on the order of plus or minus 35 metres for all three types of
satellite image regardless of pixel size. The importance of employing independent
check points for assessing the accuracy of the correction was demonstrated.
1179 Cross-Validated Assessment of Geometric Accuracy
Kenneth C. McGwire
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The recent emphasis on metadata standards must be accompanied by vigilance
in unbiased reporting of geometric accuracy. A cross- validation technique
is shown to be capable of providing more accurate estimates of geometric error
than the traditional method of using transformation residuals when modest numbers
of ground control points are available. This method also provides a much more
accurate indication of the effects of choosing different polynomial orders.
1189 Experiences with the Production of Digital Orthophotos
Joachim Höhle
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Digital orthophotos increase the potential of land and geographic information
systems considerably. In the workstations of these systems one can also produce
digital orthophotos in black and white and color. Each step of the production
process is illustrated in detail, and experience regarding the choice of parameters
in the calculation programs is stated.