Browsing by Author "Shih, Peter T. Y."

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AN EXPERIMENTAL COMPARISON OF DIRECTLY AND INDIRECTLY DERIVED MODULATION TRANSFER FUNCTIONS
(2015-03-01)
Yang, Chia-Hsiang
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Wang, Shue-Chia
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Shih, Peter T. Y.
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Lee, Pei-Shan
;
Liu, Jeng-Lun
The modulation transfer function (MTF) is the indicator most frequently used for image resolution assessment. Traditionally in photogrammetry, the MTF is directly estimated using specifically designed targets such as the USAF 1952 three-bar resolution test target, but it can also be indirectly derived from the system degradation function known as the point-spread function (PSF). Theoretically, MTF and PSF are related through a spatial-frequency domain transformation (a Fourier transformation), meaning the same attributes are expressed in different domains. When using real images, however, it is not clear whether these two functions produce the same result. In this study, both spatial and frequency domain approaches were experimentally compared through simulations. Results show that the MTF derived from the PSF has better accuracy than an MTF estimated directly from the resolution target. Resume La fonction de transfert de modulation (FTM) est l\'indicateur le plus couramment utilise pour evaluer la resolution des images. Traditionnellement, en photogrammetrie, la FTM est estimee directement au moyen de cibles speciales comme la mire de resolution a series de trois barres USAF 1952, mais elle peut egalement etre deduite indirectement de la fonction d\'etalement du point ou reponse impulsionnelle (PSF). Theoriquement, la FTM et la PSF sont liees par une transformation espace-frequence (transformation de Fourier) qui permet d\'exprimer les memes caracteristiques dans des domaines differents. Toutefois, dans le cas d\'images reelles, ces deux fonctions ne conduisent pas forcement au meme resultat. Dans cette etude, les approches dans les domaines spatial et frequentiel sont comparees experimentalement au moyen de simulations. Les resultats montrent que la FTM est estimee avec une meilleure precision a partir de la PSF que de maniere directe a partir d\'une mire de resolution. Zusammenfassung Die Modulationsubertragungsfunktion (MTF) ist der am haufigsten benutzte Indikator zur Abschatzung der Auflosung eines Bildes. Traditionell wird die Modulationsubertragungsfunktion direkt durch speziell gestaltete Zieltafeln, wie z.B. die USAF 1952 3-Balkentesttafel bestimmt; sie kann aber auch indirekt uber die Punktspreizfunktion (PSF) abgeleitet werden. Die MTF und die PSF sind theoretisch durch eine Ortsraum-Frequenzraum Transformation (eine Fourier Transformation) verbunden, d.h. die gleichen Attribute werden in unterschiedlichen Raumen ausgedruckt. Bei der Anwendung auf reale Bilder, ist aber unklar, ob diese beiden Funktionen das gleiche Ergebnis liefern. In dieser Studie wurde sowohl Ansatze im Ortsraum als auch im Frequenzraum experimentell durch Simulationen verglichen. Die Ergebnisse zeigen, dass die MTF aus PSF abgeleitet genauer ist, als seine MTF die direkt uber die Auflosungstafel bestimmt wurde. Resumen La funcion de transferencia de modulacion (MTF) es el indicador mas utilizado para la evaluacion de la resolucion de una imagen. Tradicionalmente, en la fotogrametria, la MTF se estima directamente utilizando dianas de resolucion disenadas especificamente como el USAF 1952 de tres barras, pero tambien puede ser derivada indirectamente a partir de la funcion de la degradacion del sistema conocida como funcion de dispersion de punto (PSF). Teoricamente, MTF y PSF se relacionan a traves de una transformacion de dominio espacio-frecuencia (una transformacion de Fourier), es decir, los mismos atributos se expresan en diferentes dominios. Sin embargo usando imagenes reales no esta claro que estas dos funciones produzcan el mismo resultado. En este estudio se han comparado experimentalmente, mediante simulaciones, ambos enfoques: en el dominio espacial y en el de frecuencia. Los resultados muestran que la MTF derivada de la PSF tiene mayor precision que la MTF estimada directamente a partir de la diana de resolucion. ?? ??????(MTF)??????????????,??????,???????????1952????????????????,????????????????????????(PSF)?????????,MTF?PSF?????????????????????,?????????????????????????,????MTF?PSF????????????????,?????????????????,????,?PSF???MTF?????????MTF????????
E-LEARNING - BEST PRACTICE IN PHOTOGRAMMETRY, REMOTE SENSING AND GIS - STATUS AND CHALLENGES
(2012-01-01)
Koenig, Gerhard
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Shih, Peter T. Y.
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Katterfeld, Christiane
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土木工程學系
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Department of Civil Engineering
In addition to professional training, computer aided teaching has long tradition. The difficult economic situation, however, forced many customers to take drastic austerity measures in the field of learning. Cost pressure encouraged a new openness to innovative and tailored learning concepts. As a result e-learning gained more interest and importance promising great benefit to the user. Around the world a variety of well-designed e-learning products exist. The web pages of Commission VI/2 (http://www.igg.tuberlin.de/ISPRS/) provide a decision aid to locate relevant material. Links to websites known to the authors are listed; a search function allows selective access, taking account of quality criteria. This article describes best practice e-learning applications in photogrammetry, remote sensing and GIS. The rating is based on results of the Computer Assisted Teaching CONtest (CATCON) initiated by ISPRS, and on observation of recent developments.
THE DESIGN OF AN INTERACTIVE E-LEARNING PLATFORM FOR SURVEYING EXERCISE
(2011-01-01)
Cheng, Shu-Chen
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Shih, Peter T. Y.
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Chang, Shing-Lin
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Chen, Guan-Yu
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土木工程學系
Surveying exercise is a fundamental course for Civil Engineering students. This course is featured with field operation. This study explores the design of an e-learning platform for the surveying exercise course. The issues on organizing digital contents such as recorded video of the standard instrument operation, editing learning materials, and constructing the portfolio for the learning process, as well as generating learning motivation, are discussed. Noting the uploaded videos, publishing articles and commentaries, interactive examination sessions, assessing for each other, and mobile device accessing, are found to be useful elements for this platform.
Topographic Correction of Wind-Driven Rainfall for Landslide Analysis in Central Taiwan with Validation from Aerial and Satellite Optical Images
(2013-06-01)
Liu, Jin-King
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Shih, Peter T. Y.
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土木工程學系
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Department of Civil Engineering
Rainfall intensity plays an important role in landslide prediction especially in mountain areas. However, the rainfall intensity of a location is usually interpolated from rainfall recorded at nearby gauges without considering any possible effects of topographic slopes. In order to obtain reliable rainfall intensity for disaster mitigation, this study proposes a rainfall-vector projection method for topographic-corrected rainfall. The topographic-corrected rainfall is derived from wind speed, terminal velocity of raindrops, and topographical factors from digital terrain model. In addition, scatter plot was used to present landslide distribution with two triggering factors and kernel density analysis is adopted to enhance the perception of the distribution. Numerical analysis is conducted for a historic event, typhoon Mindulle, which occurred in 2004, in a location in central Taiwan. The largest correction reaches 11%, which indicates that topographic correction is significant. The corrected rainfall distribution is then applied to the analysis of landslide triggering factors. The result with corrected rainfall distribution provides better agreement with the actual landslide occurrence than the result without correction.