USING SURFACE FITTING AND BUFFER ANALYSIS TO ESTIMATE REGIONAL GEOIDAL UNDULATION

Geoidal undulation is the distance from the surface of an ellipsoid to the surface of a geoid measured along a line that is perpendicular to the ellipsoid. This paper describes how the geoidal undulation can be derived from the orthometric height, Global Navigation Satellite System geodetic height, and a surface model. Various surfaces fitting using the plane coordinates of the reference points and analysis with different buffers were used to determine the geoid undulation Taiwan. The results show that the quadratic surface model outperformed other surface models, yielding a buffer radius ranging from 15 to 25 km. According to the results, the accuracy of regional geoid undulation (city or state) can be improved through this process of surface fitting

USING PARTICLE SWARM OPTIMIZATION TO ESTABLISH A LOCAL GEOMETRIC GEOID MODEL

There exist a number of methods for approximating the local geoid surface and studies carried out to determine a local geoid. In this study, performance of geoid by PSO method in modeling local geoid was presented and analyzed. The ellipsoidal heights (h), derived from GPS observations, and known orthometric heights from first-order bench marks were first used to create local geometric geoid model, then the PSO method was used to convert ellipsoidal heights into orthometric heights (H). The resulting values were used to compare between the spirit leveling and GPS methods. The adopted PSO method can improve the fitting of local geometric geoid by quadratic surface fitting method, which agrees with the known orthometric heights within ±1.02cmthe Cartography produced: General Map, Partial Maps, Profile, Cross Sections and others

Combining Spectral Water Indices and Mathematical Morphology to Evaluate Surface Water Extraction in Taiwan

Rivers in Taiwan are characterised by steep slopes and high sediment concentrations. Moreover, with global climate change, the dynamics of channel meandering have become complicated and frequent. The primary task of river governance and disaster prevention is to analyse river changes. Spectral water indices are mostly used for surface water estimation, which separates the water from the background based on a threshold value, but it can be challenging in the case of environmental noise. Edge detection uses a canny edge detector and mathematical morphology for extracting geometrical features from the image and effective edge detection. This study combined spectral water indices and mathematical morphology to capture water bodies based on downloaded remote sensing images. From the findings, this study summarised the applicability of various spectral water body indices to the surface water extraction of different river channel patterns in Taiwan. The normalised difference water index and the modified normalised difference water index are suitable for braided rivers, whereas the automated water extraction index is ideal for meandering rivers

USING SURFACE FITTING AND BUFFER ANALYSIS TO ESTIMATE REGIONAL GEOIDAL UNDULATION

Abstract:Geoidal undulation is the distance from the surface of an ellipsoid to the surface of a geoid measured along a line that is perpendicular to the ellipsoid. This paper describes how the geoidal undulation can be derived from the orthometric height, Global Navigation Satellite System geodetic height, and a surface model. Various surfaces fitting using the plane coordinates of the reference points and analysis with different buffers were used to determine the geoid undulation Taiwan. The results show that the quadratic surface model outperformed other surface models, yielding a buffer radius ranging from 15 to 25 km. According to the results, the accuracy of regional geoid undulation (city or state) can be improved through this process of surface fittin

The Study of Evaluating Pseudolite Assisted GPS Positioning and Error Model Analysis

GPS技術是目前廣為使用的定位及導航工具，然而GPS衛星定位存在有透空不良造成無法精確導航及定位之缺點。虛擬衛星為一個可傳播類似GPS信號之地面發射器，其可提供額外之觀測量，對於遮蔽區域之GPS定位甚有助益，其可提昇GPS定位精度並強化該系統的涵蓋面與妥善率。 目前虛擬衛星之相關研究並未全面針對其各項誤差進行研討，且未針對虛擬衛星於遮蔽區域運作之狀況及其誤差特性進行分析，因此本研究即針對虛擬衛星輔助GPS定位之多路徑效應、氣象改正、設置位置及遮蔽效益等進行研究，特別是針對遮蔽區域之運用效益及改正效應加以評估。 經本研究實地驗證虛擬衛星輔助GPS定位之結果可知，於無遮蔽區域GPS虛擬衛星之設置可使垂直坐標分量成果之重複性由2 cm提昇為1 cm，在垂直坐標成果精度上取得約50%之改善；於遮蔽處定位之效益評估，則顯示虛擬衛星觀測量之加入可提昇遮蔽區域定位精度高程精度平均約56%，平面精度平均約40%。於各項誤差效應經驗證中，虛擬衛星設置位置誤差小於5cm時之定位影響並不顯著，而與其佈設位置之幾何分佈較具相關；虛擬衛星之氣象效應及多路徑效應，分別會對定位產生影響，但因利用二次差分方式進行基線計算時，部分誤差可因此消除，故無論於遮蔽或無遮蔽區域之虛擬衛星各項誤差中僅需進行多路徑改正即可獲得最佳成果；另虛擬衛星觀測量之權重問題，經驗證其與GPS觀測量並無顯著性之差異，因此計算時可視為等權。 經由上述各項研究成果可知，本論文研究所探討之各項誤差效應影響及改正模式，可作為虛擬衛星輔助GPS定位技術發展之依據。In recently, GPS technique has become a powerful positioning and navigation tool. However, there are still some drawbacks to GPS, such as the view of sky obstructed, causing the positioning accuracy degraded. The pseudolite, a satellite-like GPS ground signal generator, is then expected to provide extra-measurements and improve the GPS accuracy, coverage, and availability at the obstructed areas. Pseudolite assisted GPS positioning in obstructed areas is seldom to discuss and research. In this study, the pseudolite error sources in obstructed area will be discussed, such as multipath, atmospheric and pseudolite location setting up error, and the positioning efficiency will be evaluated with pseudolite in the obstructed area. All the observations were processed by double difference method. The results obtained from this study show that GPS pseudolite can effectively improve the repeatability of GPS vertical component from 2 cm to 1 cm in open view sky. In addition, results obtained from this study show that precision of positioning could be promoted 56% in vertical and 40% in horizential of obstructed area. The results obtained from this study also show that the location error of pseudolite setting-up less than 5 cm does not affect the precision of positioning, but the geometric relationship between pseudolite location and observed points is related to the positioning accuracy. Research done by this study used double difference method to calculate the baseline, so most errors can be eliminated. The corrected model for pseudolite observations is focused on the multipath model, in which the result can be better than those of usin any other corrected model. The research results also show that the weight of pseudolite observations is not different to GPS observations. This study will be a guide for pseudolite assisted GPS positioning.第一章 緒論 1.1 研究目的與動機 1.2 文獻回顧 1.3 研究方法與流程 第二章 GPS虛擬衛星之運作原理 2.1 發展歷程 2.2 運作特性 2.3 基本觀測量 2.4 差分模式 2.4.1 地面一次差 2.4.2 空中一次差 2.4.3 二次差 2.5 誤差模式 2.5.1 遠近問題 2.5.2 對流層延遲誤差 2.5.3 多路徑效應 2.5.4 軌道誤差 2.5.5 衛星及接收儀時錶誤差 第三章 實驗資料獲取及計算程序 3.1 準備程序 3.1.1實驗區及測試點 3.1.2 零基線測試 3.2 虛擬衛星信號接收 3.3 虛擬衛星計算程序 第四章 遮蔽區之虛擬衛星運作效益 4.1 無遮蔽環境之測算成果36 4.1.1 各時段內成果精度之比對 4.1.2 各時段間坐標差異之比對 4.2模擬遮蔽環境之計算成果 第五章 虛擬衛星設置誤差及大氣誤差之影響分析 5.1設置誤差 5.1.1 虛擬衛星設置誤差之推估 5.1.2 設置位置誤差模擬 5.1.3 資料計算及分析 5.1.4 多顆虛擬衛星分佈之探討 5.1.5不同高度分佈位置測試 5.2大氣誤差 5.2.1氣象元素推導 5.2.2大氣誤差模式推導 5.2.3 虛擬衛星觀測量氣象改正 5.2.4成果分析 5.3 成果小結 第六章 虛擬衛星觀測量改正及加權效益之評估 6.1 GPS虛擬衛星多路徑效應影響 6.1.1 虛擬衛星多路徑效應實驗數據蒐集 6.1.2 實驗成果分析 6.2 綜合多路徑與大氣誤差改正之效益 6.2.1 實驗數據與處理 6.2.2 實驗分析 6.2.3 各項改正組合實驗成果 6.3 GPS虛擬衛星觀測量之加權效益分析 6.3.1 無遮蔽區域 6.3.2 遮蔽區域 6.3.3 加權效益分析成果 6.4 成果小結 第七章 虛擬衛星佈設點位分析工具之開發 7.1 資訊分析模式 7.1.1 衛星站心坐標系統計算 7.1.2 衛星精度稀釋量 7.1.3 遮蔽率計算 7.1.4 空間分析模組 7.2成果展示 第八章 結論與建議 8.1 結論 8.2建

Low-Cost Indoor Positioning Application Based on Map Assistance and Mobile Phone Sensors

Current mainstream navigation and positioning equipment, intended for providing accurate positioning signals, comprise global navigation satellite systems, maps, and geospatial databases. Although global navigation satellite systems have matured and are widespread, they cannot provide effective navigation and positioning services in covered areas or areas lacking strong signals, such as indoor environments. To solve the problem of positioning in environments lacking satellite signals and achieve cost-effective indoor positioning, this study aimed to develop an inexpensive indoor positioning program, in which the positions of users were calculated by pedestrian dead reckoning (PDR) using the built-in accelerometer and gyroscope in a mobile phone. In addition, the corner and linear calibration points were established to correct the positions with the map assistance. Distance, azimuth, and rotation angle detections were conducted for analyzing the indoor positioning results. The results revealed that the closure accuracy of the PDR positioning was enhanced by more than 90% with a root mean square error of 0.6 m after calibration. Ninety-four percent of the corrected PDR positioning results exhibited errors of <1 m, revealing a desk-level positioning accuracy. Accordingly, this study successfully combined mobile phone sensors with map assistance for improving indoor positioning accuracy

Combination of VSLAM and a Magnetic Fingerprint Map to Improve Accuracy of Indoor Positioning

With the continual advancement of positioning technology, people′s use of mobile devices has increased substantially. The global navigation satellite system (GNSS) has improved outdoor positioning performance. However, it cannot effectively locate indoor users owing to signal masking effects. Common indoor positioning technologies include radio frequencies, image visions, and pedestrian dead reckoning. However, the advantages and disadvantages of each technology prevent a single indoor positioning technology from solving problems related to various environmental factors. In this study, a hybrid method was proposed to improve the accuracy of indoor positioning by combining visual simultaneous localization and mapping (VSLAM) with a magnetic fingerprint map. A smartphone was used as an experimental device, and a built-in camera and magnetic sensor were used to collect data on the characteristics of the indoor environment and to determine the effect of the magnetic field on the building structure. First, through the use of a preestablished indoor magnetic fingerprint map, the initial position was obtained using the weighted k-nearest neighbor matching method. Subsequently, combined with the VSLAM, the Oriented FAST and Rotated BRIEF (ORB) feature was used to calculate the indoor coordinates of a user. Finally, the optimal user’s position was determined by employing loose coupling and coordinate constraints from a magnetic fingerprint map. The findings indicated that the indoor positioning accuracy could reach 0.5 to 0.7 m and that different brands and models of mobile devices could achieve the same accuracy