1,720,985 research outputs found
Efficient Rendering Techniques for Approximated Illumination
No full text照明對影像生成來說是個很重要的關鍵。從即時渲染，互動式渲染到光傳輸模擬，這些領域根據不同的應用目的試圖提升效率。在本論文中，我們將從硬體架構到演算法的角度介紹所提出的高效率渲染方法，主要為渲染高品質之照明效應。 本論文從一個感知功率的GPU繪圖管線架構開始介紹。從硬體的角度看來，我們想減少像素線程以節省順向渲染管線中之處理器功耗。主要因為照明通常是平順地分布在物體表面，所以我們想透過稀疏取樣像素執行像素照明，並且在繪圖管線中的光柵處理單元(ROP)以片狀單位(per tile basis)內插未被渲染之像素。所提出之屏幕近似照明方法實現在一顆十六核心行動裝置處理晶片原型，透過台積電45奈米製程實作。在我們的評估下，當執行順向照明時，處理器的執行比例可減少40%~50%。 基於硬體實作的方法是簡化的濾波技巧，並且受限於片狀單位處理。所以我們延伸自硬體方法，提出了一個基於屏幕空間的感知幾何濾波方法來重建稀疏照明之像素。透過隨機稀疏取樣，並照明屏幕空間上的像素，我們所提出之屏幕照明近似方法考慮幾何關係，譬如法向量以及位置做像素重建。實驗結果，平均來說，我們可以僅渲染20%~30%之屏幕像素並獲得令人滿意的重建品質。 更進一步，我們考慮了間接照明，以提供在即時或者互動渲染應用之全域照明效應來提升渲染真實度。除了直接照明，我們近似第一碰撞間接照明。所提出的技巧基於簡化後的點狀幾何，並透過體素格來索引。透過稀疏之光行進法，我們能檢查遮蔽體素，更進一步，我們提出了可視度濾波器來結合可視體素以平滑可視度估計。接著，我們能利用可能的點狀光源來近似第一碰撞間接照明。效能上來說，我們所提出之方法能提供間接照明之互動效能約為每秒1~2片幀。 最後，我們延伸點狀幾何來近似路徑追跡。為了有效率地找出光與幾何之交集點以連結路徑頂點，我們提出了一個混合查閱結構。這個查閱結構結合了點，叢集平面以及體素格。透過使用基於體素格的查閱，我們可以獲得一個粗略體素格，透過此粗略估計我們可以透過此查閱結構區域性地查閱並連結可能的路徑頂點。實驗結果，我們能在幾秒內快速減少生成影像之變異度，達到高品質的影像生成結果。 透過我們的實驗結果，從硬體到平行實作的角度，我們提出的方法在即時圖像到光傳輸模擬之領域都能達到很高的效能，同時兼顧並達到令人滿意之影像生成品質。總的來說，本論文可以視為主要在高效率渲染之近似照明領域的完整討論。Illumination is essential for synthesizing images. From real-time rendering, interactive rendering to light transport simulation, these fields exploit efficiency in producing illumination according to different application targets. In this dissertation, we will introduce our efficient rendering techniques for rendering illumination with plausible quality, from architecture to algorithm perspective. The dissertation starts from exploiting a power-aware rendering architecture for a conventional GPU pipeline. From hardware perspective, we aim at reducing the pixel threads to save processor power dissipation in the forward rendering pipeline. Since illumination usually reveals smooth variation, instead of lighting every rasterized pixel, we sparsely sample pixels for lighting and interpolate the un-shaded pixels per tile basis during ROP phase. The screen-space approximated lighting technique is realized in a 16-core mobile GPU chip prototype, which is fabricated with TSMC 45nm technology. In our evaluation, the processor execution can reduce about 40% to 50% while performing forward lighting. The hardware-based approach is a simplified filtering technique and limited by the tile basis. Extended from the hardware-based approach, we propose a screen-space geometry-aware bilateral filter for sparsely lit pixels. With randomly illuminated screen pixels, the screen-space lighting approximation considers deferred geometric properties, including normal and position. Empirically, we can merely shade 20% to 30% screen pixels in average with satisfactory reconstruction quality. Moreover, indirect illumination is the soul of global illumination which enhances the visual realism for either real-time or interactive rendering applications. In addition to direct illumination, we approximate the first bounce indirect illumination. Our technique is based on a simplified point-based geometry, which is indexed via voxel grids. Through sparse ray marching for examining occluded voxels, we propose a visibility filter for associating batches of visible voxels to smooth visibility estimation. Therefore, the first bounce indirect illumination can be approximated with the possible point light sources. Regarding performance, the proposed technique can produce indirect illumination in an interactive rate from 1 to 2 fps. Ultimately, we extend the point-based geometry to approximate path tracing. To efficiently query the intersection for vertex connection, we propose a hybrid lookup hierarchy. The lookup structure is composed of point samples, clustered planes and voxel grids. Through utilizing a voxel-based query approach on coarse voxels, the rough estimate can be used for locally connecting the possible path vertex via the lookup structure. As a result, the variance of a synthesized image can be rapidly reduced in a few seconds with plausible visual quality. Our evaluation reveals compelling performance results, from architecture to parallel implementations, from real-time graphics to light transport simulation, meanwhile delivering plausible visual quality. In summary, the dissertation can be regarded as an extensive study in major efficient rendering topics for approximated illumination
Design and analysis of a GPS tracking loop controller with Doppler effect compensation
No full text本論文先對全球衛星定位系統作一個概略的敘述，接著介紹系統中接收機處理信號的流程，描述各個步驟的分工與合作狀況，再針對處理流程中的信號追蹤步驟加以討論，最後設計一個追蹤迴路控制器去完成整個信號追蹤的過程。 信號追蹤的過程中，首先是加上一個督卜勒效應補償器，讓衛星信號在太空中傳遞時受到督卜勒效應的影響減小，以方便後續處理衛星信號中電碼相位漂移的部份。經過督卜勒補償之後將信號分段，分成長度一到二十個毫秒不等的訊框與本地產生之不同延遲的C/A碼複製版本作相關係數的運算。每個訊框的運算結果中，將最高相關係數絕對值對應的相位其延遲量記為此訊框所對應的相位漂移。在每一段時間中，將訊號切割成數十到數百個訊框並作上述相位判定的工作之後，可以得到相位漂移的特徵，也就是相位會隨著時間慢慢改變。而依照相位漂移與督卜勒效應的關係，可以用找出相位漂移所對應的最小方差直線以求出此時的督卜勒效應的估計值，以利進行下一次追蹤迴路。 最後，本論文分析了本追蹤迴路在選取不同訊框長度時，對於雜訊強度的承受度。在整理六種不同訊框長度對應的雜訊承受極限後，得出一個可以概估兩者關係的式子，並且探討其意義。最後也對於不同訊框長度下，所需要的計算量作一個比較。This thesis starts by making a brief description about the Global Positioning System (GPS), and introduces how the signal processing task in GPS receivers is divided into sub-tasks and accomplished as a whole. Then, the tracking loop in the GPS signal processing sub-system is particularly addressed. Finally, a tracking loop controller is designed specifically for the signal processing purpose. In the tracking loop, a Doppler effect compensator is added first to suppress the Doppler effect on signals transmitting in the outer space. This makes it easier to deal with the signals subsequently, such as the phase shift of C/A code in the satellite signal. The step taken after Doppler compensation is to divide a signal into frames with different lengths, from 1 to 20 milliseconds, and to compute the correlation coefficients between frames and locally generated C/A code copies with different phase delays. In every computation result, the phase shift is recorded according to the highest absolute value of correlation coefficient, so that the trace of phase shift can be obtained, which represents phase changes as time passing. Based on the relationship between code phase shift and Doppler effect, the estimated value of Doppler effect can be counted by finding the least-square line from the code phase shift and time, and can be used in tracking loop for the next iteration. The thesis finishes with the analysis of noise margin using different frame lengths. After summarizing the relation between all six kinds of frame length and noise margin, an equation can be obtained to estimate one with the other. Besides, the total calculation effort with different frame length is discussed.目錄......................................................i目錄..................................................iii目錄....................................................v一章 緒論..1 1.1 研究動機...1 1.2 文獻回顧與探討..1 1.3 論文架構..3二章 全球衛星定位系統簡介..5 2.1 GPS衛星、軌道及其他相關設備..5 2.2 信號結構與模擬..5 2.2.1 信號的結構..5 2.2.2 信號產生..6 2.2.3 PRN 序列的產生..9 2.3 射頻信號與中頻信號11 2.4 擷取信號..13 2.5 追蹤信號..17 2.6 導航資料的解算與定位..17三章 GPS信號的追蹤..19 3.1 追蹤迴路的結構..19 3.2 信號解調變..19 3.3 電碼追蹤迴路..21 3.4 載波追蹤迴路..23 3.5 完整的追蹤迴路..25四章 追蹤迴路的分析與設計..27 4.1 基頻輸入信號的產生..27 4.2 相關係數運算與相關性質..30 4.3 督卜勒效應造成的相位漂移..32 4.4 信號的相位漂移..34 4.5 追蹤迴路設計架構..35 4.5.1 督卜勒補償..36 4.5.2 相位比較器..38 4.5.3 相位判定..39 4.5.4 督卜勒決定器..41五章 追蹤迴路模擬..435.1 加入雜訊與模擬..435.2 訊框長度1ms的模擬..44 5.3 訊框長度5ms的模擬..46 5.4 訊框長度10ms的模擬..48 5.5 訊框長度20ms的模擬..49 5.6 總結..50六章 結論以及未來展望..53 6.1 結論與分析..53 6.1.1 訊框長度與雜訊忍受極限..53 6.1.2 式6.1結果與分析討論..54 6.1.3 計算量的比較..55 6.1.4 小結..566.2 未來展望..56考文獻..5
Sensor-Assisted Human Mobility Model Estimation forarticle-Filter-Based Location System
No full text高齡化社會成為了現今共同的問題，老年人照護的議題也隨著日益重要。養護中心提供了一個老年人安全監控以及集中照護的社群。雙連安養中心也是其中之一，集中照護超過350位長者。安養中心提供了各式的照護服務，不過，最重要的問題仍在老年人的安全。為了監控這麼大數量的長者，人力資源的成本必須花費相當大。 們應用了以RSSI(接收信號強度)為基礎的定位系統來幫助安全監控的問題。定位的演算法是以KNN估測為基礎，加上粒子濾波器使得定位點輸出流暢化。但KNN估測很容易被無線信號強度的不穩定性所影響，這會使得定位精確度大幅下降。粒子濾波器便是用以解決這個問題。但戶外環境和室內環境是有很大的不同。 在室內環境裡，人的移動受限於有限的空間限制。所以在粒子濾波器中的移動模型，只要設定在一個平均的移動率即足以克服室內環境裡人的各種行動模式。然而，人們再是外會有各種不同的行動模式，譬如跑步、慢跑、走路等。在室外的環境中很容易會有比較極端的移動模式。若將行動模型設定在一個平均值上恐怕不足以解決粒子濾波器中追蹤的問題。這篇論文找出了一個利用附加加速度器的方法來收集加速度值，並且利用利用FFT(快速傅立葉轉換)來分析資料。藉此，我們可以找出監控目標的步頻，乘上目標的步距，即可線上估測目標速度。利用這個速度的估計值，粒子濾波器也可以同時調整定位估測所使用的行動模型，進而提升定位精確率。Nowadays, aging population becomes a common problem in the world. Elderly caring is a getting emphasized issue. Nursing center turns out to be a community for elderly people to centralize safety monitoring and caring. Suang-lien nursing center is one of them. There are over 350 members reside in it. The nursing center provides a wide variety of caring services for elderly people, hence the most important problem is their safety concern. In order to monitoring large amount of the elderly people, human resource on the caring is costly. e apply our RSSI based localization system to help safety monitoring. Our localization algorithm is based on KNN estimation plus particle filter to smooth position output. The KNN estimation is easily affected by wireless signal instability, which devastates the location accuracy. Thus the particle filter is used to solve the issue. Outdoor environment is much different than indoor. In indoor environment, human moves within the restriction of limited space. Therefore, set the mobility model inside particle filter with average mobility is enough to solve human moving patterns in indoor environment. However, human might have various mobility patterns in outdoor, including running, jogging, walking…etc. Extreme mobility cases are easily to occur in outside environment. Set the mobility in average case is not enough to solve the tracking problem. Our work comes up an idea that we could use an extra added accelerometer and analyze acceleration values by FFT. After that, we could get the target stride frequency, and multiply with target’s stride length. The target speed can be approximated on-line. With the speed approximation, the particle filter can simultaneously adjust the mobility model for position estimation, therefore, enhance the location estimation accuracy.誌謝 i文摘要 iiBSTRACT iiiONTENTS vIST OF FIGURES viiIST OF TABLES ixhapter 1 Introduction 1hapter 2 Related Work 3hapter 3 Problem Formulation 7.1 Recursive Bayesian Filtering 7.2 Monte Carlo Approximation 10hapter 4 Sensor-assisted Human Tracking 13.1 Accelerometer-based Step Counting 13.1.1 Observation 13.1.2 Inferring the Stride Frequency 14.2 Mobility Aware Particle Filtering 16hapter 5 Implementation 18.1 Hardware 18.2 Fix-Point FFT 19.2.1 FFT Implementation 19.2.2 Radix-2 DIT 256-Point FFT 21.2.3 Input Reorder 22.2.4 Sin/Cos LUT and Fix-Point Computation 23.3 Adapting Mobility Model 25hapter 6 Experiment 28.1 Testbed 28.2 Location System 29.3 Experiment Setting 29hapter 7 Evaluation 33.1 Stride Frequency Estimation Accuracy 33.2 Location Estimate Accuracy 36.3 Synthesized Test – Speed Variation 40.4 Fine-Grain Speed Bound Simulation 42.5 Stride Length Setting Effect 44hapter 8 Conclusion 48EFERENCE 5
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
