Browsing by Author "Shih, TY"

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A photogrammetric simulator for close-range applications
(1996-01-01)
Shih, TY
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交大名義發表
;
土木工程學系
;
National Chiao Tung University
;
Department of Civil Engineering
Simulation is an important process for project design. An algorithm specifically designed for close-range applications is described in this study. This algorithm, based on human behavior, simulates the hand-held camera situation. The algorithm and a numerical example are presented. An implementation into a CAD system has been attempted, in which the initial results are rather encouraging.
A quality assurance approach for land subsidence interpolation
(2002-10-01)
Peng, MH
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Shih, TY
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土木工程學系
;
Department of Civil Engineering
Land subsidence in southwest Taiwan is mainly caused by ground-water withdrawal and a monitoring network of benchmarks has been established to observe this subsidence. Using results from differential leveling, the magnitudes of land subsidence from 1992 to 7994 were calculated for 50 benchmarks. The calculated maximum magnitude of land subsidence is 15.4 centimeters between these two years. Spatial interpolation is frequently required to provide information for assessing the distribution and extent of subsidence. In this study, geostatistics were applied to describe and characterize the spatial structure of sample data. Thus, an implementation procedure was proposed for the quality assessment of interpolation. The procedure includes geostatistical analysis, outlier detection, and comparison of different estimation techniques. The results,chow that the approach proposed in this study is effective to ensure the quality of interpolation.
Effects of JPEG 2000 compression on automated DSM extraction: Evidence from aerial photographs
(2005-12-01)
Shih, TY
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Liu, JK
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交大名義發表
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National Chiao Tung University
This paper evaluates the effects of JPEG 2000 compression on automated digital surface model (DSM) extraction, using the area-based matching technique. Two stereopairs of aerial photographs, which have different photo scale, pixel size, and topographic type, are used as the images for the experiments. In the experiments, the DSM generated from the uncompressed image is set as the reference, and the elevation accuracy is computed for a range of compression ratios (2:1 to 100:1). The results show that the employed indices of image quality based on the JPEG 2000 compression are clearly superior to the commonly used JPEG compression technique-especially for high compression ratios. However, the elevation accuracy varies with the compression ratios. Also, JPEG 2000 compression does not have a significant influence on the percentage of the successful matching rate. In addition, a near linear fall-off is observed in extracted DSM accuracy with increasing compression ratios.
Effects of JPEG2000 on the information and geometry content of aerial photo compression
(2005-02-01)
Liu, JK
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Wu, HC
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Shih, TY
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土木工程學系
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Department of Civil Engineering
The standardization effort of the next ISO standard for compression of the still image, JPEG2000, has recently reached International Standard (IS) status. This wavelet-based standard outperforms the Discrete Cosine Transform (DCT) based JPEG in terms of compression ratio, as well as, quality. In this study, the performance of JPEG2000 is evaluated for aerial image compressions. Different compression ratios are applied to scanned aerial photos at the 1:5000 scale. Both the image quality measurements and the accuracy of photogrammetric point determination aspects are examined. The evaluation of image quality is based on visual analysis of the objects in the scene and on the computation of numerical indices, including RMSE, entropy, and Peak Signal-to-Noise Ratio (PSNR). The geometric quality of JPEG2000 with different compression ratios is studied for some photogrammetric operations, including interior orientation, relative orientation, absolute orientation, and DSM generation. The objective of this study is to explore the possibility of JPEG2000 for replacing JPEG as a standard in photogrammetric operations.
Improvements on Sloan's algorithm for constructing Delaunay triangulations
(1998-03-01)
Huang, CW
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Shih, TY
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土木工程學系
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Department of Civil Engineering
Large earthquake-triggered landslides and mountain belt erosion: The Tsaoling case, Taiwan
(2005-09-01)
Chen, RF
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Chan, YC
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Angelier, J
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Hu, JC
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Huang, C
The 1999 Chi-Chi earthquake triggered the catastrophic Tsaoling landslide in central Taiwan. We mapped the landslide area and estimated the landslide volume, using high-resolution digital elevation model from airborne LiDAR (Light Detection and Ranging), satellite images, aerial photographs and topographic maps. The comparison between cut and fill volumes, about 0.126 and 0.150 km(3), respectively, suggests a volume increase of 19% due to decompaction during landsliding. In April 2002, the cut and fill volumes were about 0.137 and 0.116 km(3), respectively. These estimates suggest that 2.5 years after the event, the volume of landslide debris removed by river erosion was nearly 0.045 km(3). Such a large value highlights the importance of landslide processes for erosion and long-term denudation in the Taiwan mountain belt.
On the complexity of point-in-polygon algorithms
(1997-02-01)
Huang, CW
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Shih, TY
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土木工程學系
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Department of Civil Engineering
Point-in-polygon is one of the fundamental operations of Geographic Information Systems. A number of algorithms can be applied. Different algorithms lead to different running efficiencies. In the study, the complexities of eight point-in-polygon algorithms were analyzed. General and specific examples are studied. In the general example, an unlimited number of nodes are assumed; whereas in the second example, eight nodes are specified. For convex polygons, the sum of area method, the sign of offset method, and the orientation method is well suited for a single point query. For possibly concave polygons, the ray intersection method and the swath method should be selected. For eight node polygons, the ray intersection method with bounding rectangles is faster. (C) 1997 Elsevier Science Ltd.
On the complexity of point-in-polygon algorithms
(1997-02-01)
Huang, CW
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Shih, TY
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
Point-in-polygon is one of the fundamental operations of Geographic Information Systems. A number of algorithms can be applied. Different algorithms lead to different running efficiencies. In the study, the complexities of eight point-in-polygon algorithms were analyzed. General and specific examples are studied. In the general example, an unlimited number of nodes are assumed; whereas in the second example, eight nodes are specified. For convex polygons, the sum of area method, the sign of offset method, and the orientation method is well suited for a single point query. For possibly concave polygons, the ray intersection method and the swath method should be selected. For eight node polygons, the ray intersection method with bounding rectangles is faster. (C) 1997 Elsevier Science Ltd.
The fractal properties of sea surface topography derived from TOPEX/POSEIDON (1992-1996)
(1999-11-01)
Shih, TY
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Hwang, JT
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Tsai, TJ
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土木工程學系
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Department of Civil Engineering
Fractal dimension with various algorithms has increasing applications in characterizing both linear and areal features. In this study, the variabilities of sea surface topography derived from TOPEX/POSEIDON are studied. The variogram method is applied to compute fractal dimensions for each scene. Cumulatively, 29 scenes taken from 1992, 111 scenes taken from 1993, 110 scenes from 1994, 98 scenes taken from 1995 and 38 scenes taken from 1996 are analyzed. The spatial resolution of each scene is two degrees along both longitudinal and latitudinal directions. The annual averages of fractal dimensions are 2.528, 2.527, 2.523, 2.523 and 2.524 for 1992, 1993, 1994, 1995 and 1996, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.
The performance of GPS Standard Positioning Service without selective availability
(2001-07-01)
Shih, TY
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Shih, HY
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Yang, M
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土木工程學系
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Department of Civil Engineering
The accuracy of the Standard Positioning Service of GPS has greatly improved after the termination of Selective Availability. Based on GPS observations from permanent GPS-fixed stations, the actual accuracy of GPS without SA is analyzed. For Station NCTU, the local geodetic coordinates are computed with the C/A code pseudo-ranges, and then transformed into a local grid system with Trans-Mercator projection. From 77984 single epoch observations collected in twenty-nine days, the 95% accuracy is found to be DeltaE : 17.6544m, DeltaN : 11.8236, DeltaH : 31.8018m. For five selected UNAVCO stations, the axes of error ellipsoid are computed.
The sign permutation in the rotation matrix and the formulation of the collinearity and coplanarity equations
(1996-10-01)
Shih, TY
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交大名義發表
;
土木工程學系
;
National Chiao Tung University
;
Department of Civil Engineering
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.