Browsing by Author "Shih, Tian-Yuan"

Now showing 1 - 10 of 10

A performance evaluation of the internet based static GPS computation services
(2007-04-01)
Liu, Jung-Hon
;
Shih, Tian-Yuan
;
土木工程學系
;
Department of Civil Engineering
In conventional relative GPS surveying, users must use at least two sets of GPS receivers, as well as the associated processing software packages. This is not only a hardware or software constraint, but also a logistical problem. Furthermore, in many instances the data processing steps may be more difficult for users with limited experience in GPS technology. These problems can be resolved with an Internet GPS Service, whereby the user can finish all of the processes with only one GPS receiver without the need to use a base-station or to buy and maintain any data processing software. This study explores the usage of internet-based GPS services. Two fixed stations, NCTU and DONS established by National Chiao Tung University and National Cheng Kung University respectively, were used. The observation period was from 2001/3/1 to 2001/3/31. To establish the reference data set, the IGS station WUHN and PIMO were used as reference stations in order to compute the NCTU and DONS positions with daily observation from 2001/3/1 to 2001/3/7. The average of the seven daily positions is then used as the reference data set. The subdivided set of data sets, taken at intervals of 24, 6, 4 and 2 hours, were then processed with the Internet GPS Services. The results are evaluated using mean absolute error, maximum absolute error and minimum absolute error. In this paper, with the situation of an observation interval of 24 hours, the differences of horizontal coordinates computed from all Internet GPS Services are in the cut range, but the resultant height values vary, some within the 2 similar to 3 cm range, and some within the 10 similar to 20 cm range. For the baseline of 170286.0442m, the error is +/- 29.63mm.
A STATISTICAL ANALYSIS FOR CHARACTERIZING LANDSLIDE CAUSED BY HEAVY RAINFALL AND SEVERE EARTHQUAKE
(2013)
Chang, Kuan-Tsung
;
Liu, Jin-King
;
Hsu, Wei-Chen
;
Shih, Tian-Yuan
;
土木工程學系
Heavy rainfall and earthquakes are the two major factors inducing landslides in Taiwan. The distribution of area size is the most basic quantitative parameter of landslides. Therefore, the purpose of this study is to characterize the scale and spatial difference of rainfall-induced as compared with those of earthquake-induced landslides. Two representative landslide cases, Toraji typhoon occurred in 200 1 and 921 earthquake occurred in 1 999, are used to analyze the causes of different kinds of landslide disasters in the paper. The test area for the 921 earthquake case is 3700 km(2), the recognized number of landslide in the event is 7279, and total area for the landslides is 1 4766 Ha. Moreover, the maximum area of one landslide is 532 Ha, the average area for the landslides is 2 Ha, and its corresponding standard deviation is 1 3 Ha. In the test case of Toraji typhoon, the total study area is 8847 km(2), the number of landslides is 1 0359, and total area for the landslide is 22305 Ha. The maximum area of a landslide is 232 Ha, the average area for the landslides is 2.2 Ha, and its corresponding standard deviation is 6.2 Ha.
Characterizing the Hsincheng active fault in northern Taiwan using airborne LiDAR data: Detailed geomorphic features and their structural implications
(2007-11-15)
Chan, Yu-Chang
;
Chen, Yue-Gau
;
Shih, Tian-Yuan
;
Huang, Chung
;
土木工程學系
We applied newly acquired high-resolution airborne LiDAR data to study a segment of the Hsincheng fault, a well-known active fault near a large industrial park in northern Taiwan. The Hsincheng fault has received much attention and study in the past; but high spatial resolution digital elevation models have not previously been applied to the study of the fault and its surrounding structures. We processed the acquired LiDAR data and produced I in digital elevation models (DEMs) to investigate the active fault adjacent to the densely populated and important infrastructure in Taiwan. Using the LiDAR DEMs, aerial photographs and topographic maps, we show highly detailed geomorphic characteristics around the study area of the Hsincheng fault. Three major characteristics of the study area are defined that include three very well preserved river terraces at varying levels, the fault/fold scarp of the Hsincheng fault, and meandering river systems. Using the LiDAR DEMs, we were able to detect with precision several fault/fold scarps and very gentle NE-trending folding of the river terraces. In general, the LiDAR DEMs have provided unprecedented clarity of landforms for one segment of the Hsincheng fault, which has helped the characterization of subtle but important geomorphic features. (c) 2007 Elsevier Ltd. All rights reserved.
Error assessment in two lidar-derived TIN datasets
(2006-08-01)
Peng, Miao-Hsiang
;
Shih, Tian-Yuan
;
土木工程學系
;
Department of Civil Engineering
An accuracy assessment of two lidar-derived elevation datasets was conducted in areas of rugged terrain (average slope 26.6 degrees). Data from 906 ground checkpoints in various land-cover types were collected in situ as reference points. Analysis of the accuracy of lidar-derived elevation as a function of several factors including terrain slope, terrain aspect, and land-cover types was conducted. This paper attempts to characterize vegetation information derived from lidar data based on variables such as canopy volume, local roughness of point clouds, point spacing of lidar ground returns, and vegetation angle. This information was used to evaluate the accuracy of elevation as a function of vegetation type. The experimental results revealed that the accuracy of elevation was considerably correlated with five factors: terrain slope, vegetation angle, canopy volume, local roughness of point clouds, and point spacing of lidar ground returns. The results show a linear relationship between the elevation accuracy and the combination of vegetation angle and the point spacing of ground returns (r(2) > 0.9). The combination of vegetation angle and point spacing of ground returns explains a significant amount of the variability in elevation accuracy. Elevation accuracy varied with different vegetation types. The elevation accuracy was also linearly correlated with the product of the point spacing of ground returns and the tangent of the slope (r(2) = 0.9). A greater product value implies a greater elevation error. In addition, with regard to terrain aspect, one dense dataset with extra cross-flight data revealed a lesser impact Of aspect on elevation accuracy.
Estimation of Blufflines Using Topographic Lidar Data and Orthoimages
(2009-01-01)
Liu, Jung-Kung
;
Li, Rongxing
;
Deshpande, Sagar
;
Niu, Xutong
;
Shih, Tian-Yuan
Coastal zone mapping, particularly of shorelines, is critical for safe navigation, resource management, environmental protection, and sustainable coastal development. This paper explains a method for extracting coastal blufflines where airborne lidar (Light Detection and Ranging) data is integrated with orthoimages. A historical Lake Erie bluff top line was used as a reference line and a series of transects created perpendicular to it. After three-dimensional elevation Profiles of these transects were obtained from a lidar DSM (digital surface model), a new algorithm was used to extract from these transects initial points identifying bluff top and toe. These points were connected to form an initial bluffline. The horizontal position of this initial bluffline was refined with edges obtained from the orthoimages using techniques including mean-shift segmentation, surface reconstruction, and edge detection. Results show this method is capable of deriving blufflines having a similar quality to that from manual digitization.
LANDSLIDE DETECTION BY INDICES OF LIDAR POINT-CLOUD DENSITY
(2010)
Liu, Jin-King
;
Hsu, Wei-Chen
;
Yang, Mon-Shieh
;
Shieh, Yu-Chung
;
Shih, Tian-Yuan
The deliverables of an airborne LiDAR survey usually include all points, ground points, digital surface models (DSM) and digital elevation models (DEM). Indices of point clouds tested in this study include density of all points, density of ground points, density of only returns, and density of multiple returns. Shallow landslides are the most common landslides triggered by torrential rainfalls and explicit fresh scars after rainfall events. Multiple returns in forest area give the possibility of differentiating landslide scars from vegetated lands. Classification results from the indices derived from these four kinds of densities are verified by the result obtained by manual interpretation of the derived nDSM images. The experiment is carried out using the dataset obtained in I-Lan County after Typhoon Kalmaegi on 17 July 2008. The results show that a proper definition of the parameters for the indices is most critical for the detection of shallow landslides.
Lidar DEM for characterizing the volcanic landforms of Tatun Volcanoes in Metropolitan Taipei
(2007)
Liu, Jin-King
;
Chan, Yu-Chang
;
Shih, Tian-Yuan
;
Hsieh, Yu-Chung
;
土木工程學系
Tatun Volcano Group is a cluster of dormant volcanoes surrounding Metropolitan Taipei. Rugged terrain, monotonic lithology and dense vegetation covers are adverse factors for mapping the geological structures. In this study, airborne Lidar survey was conducted to obtain a bare ground DEM with 2m grid and with an accuracy of decimeters. Shaded-relief images, pit-patterns and drainage networks are then derived from these DEMs for visual interpretation. 51 volcanoes are thus recognized. Two fissures running through the highest volcano in this area, namely Mount Seven-stars, are extending 2000m and 1000m, respectively. The largest width and depth of the opening of the ruptures is located in the west flank of the volcanic cone. The slope angle of the cast-wing of the volcanic cone is 36 degrees, whereas the angle of the west-wing is only 24.5 degrees. The opening of the west fissure is larger and its extension is longer than the east one. Thus, the west side can be subjected to an active extensional process of strain. The fissures could be resulted from the ongoing regional extension of the Tatun Volcanic area due to the plate subduction and collision of the Eurasian Plate and the Philippine Sea Plate.
Lidar-based change detection and change-type determination in urban areas
(2013)
Teo, Tee-Ann
;
Shih, Tian-Yuan
;
土木工程學系
;
生物科技學系
;
Department of Civil Engineering
Change detection of objects, such as buildings, is essential for map updating. Traditionally, detection is usually performed through spectral analysis of multi-temporal images. This article proposes a method that employs multi-temporal interpolated lidar data. The objective of this study is to perform change detection and change-type determination via geometric analysis. A shape difference map is generated between the digital surface models in two different time periods. The areas with small shape differences are treated as non-changed areas and are excluded from the segmentation. The object's properties are then applied to determine the change types. Experimental results demonstrate that the proposed scheme achieves accuracy as high as 80%. Most of the errors from this study occurred in small or vegetation areas.
Using differential SAR interferometry to map land subsidence: a case study in the Pingtung Plain of SW Taiwan
(2011-09-01)
Hsieh, Chia-Sheng
;
Shih, Tian-Yuan
;
Hu, Jyr-Ching
;
Tung, Hsin
;
Huang, Mong-Han
Synthetic aperture radar (SAR) interferometry (InSAR) is a geodetic tool widely applied in the studies of earth-surface deformation. This technique has the benefits of high spatial resolution and centimetre-scale accuracy. Differential SAR interferometry (DInSAR) is used to measure ground deformation with repeat-pass SAR images. This study applied DInSAR and persistent scatterers InSAR (PSInSAR) for detecting land subsidence in the Pingtung Plain, southern Taiwan, between 1995 and 2000. In recent years, serious land subsidence occurred along coastal regions of Taiwan as a consequence of over-pumping of underground water. Results of this study revealed that the critical subsidence region is located on the coast near the estuary of Linpien River. It is also found that subsidence was significantly higher during the dry season than the wet season. The maximum annual subsidence rate of the dry season is up to -11.51 cm/year in critical subsidence region and the vertical land movement rate is much slower during the wet season. The average subsidence rates in wet and dry seasons are -0.31 and -3.37 cm/year, respectively. As a result, the subsidence rate in dry seasons is about 3 cm larger than in wet seasons.
以透水光達測繪技術測製東沙地區數值地形模型工作
(2009)
史天元
;
Shih, Tian-Yuan
;
國立交通大學{防災與水環境研究中心}
我國國內目前尚未有「測深光達」儀器設備，相關技術亦在引進階段。本計畫包含東沙環礁與澎湖兩個地區，作業包含測深光達實際作業與精度驗證計畫。除了完成可靠之水深資料建置外，亦將促進我國測繪技術發展。除達成數據取得、培訓數據處理與分析能力之目標，更期望能夠直接將數據引入應用，從而發揮經濟效益。