1,188 research outputs found
Geometric distance fields of plane curves
This paper introduces a geometric generalization of signed distance fields for plane curves. We propose to store simplified geometric proxies to the curve at every sample. These proxies are constructed based on the differential geometric quantities of the represented curve and are used for queries such as closest point and distance calculations. We investigate the theoretical approximation order of these constructs and provide empirical comparisons between geometric and algebraic distance fields of higher order. We apply our results to font representation and rendering
Compressed Coverage Masks for Path Rendering on Mobile GPUs
We present an algorithm to accelerate resolution independent curve rendering on mobile GPUs. Recent trends in graphics hardware have created a plethora of compressed texture formats specific to GPU manufacturers. However, certain implementations of platform independent path rendering require generating grayscale textures on the CPU containing the extent that each pixel is covered by the curve. In this paper, we demonstrate that generating a compressed grayscale texture prior to uploading it to the GPU creates faster rendering times in addition to the memory savings. We implement a real-time compression technique for coverage masks and compare our results against the GPU-based implementation of the highly optimized Skia rendering library. We also analyze the worst case properties of our compression algorithms. We observe up to a 2 × speed improvement over the existing GPU-based methods in addition to up to a 9:1 improvement in GPU memory gains. We demonstrate the performance on multiple mobile platforms
Severe plastic deformation of difficult-to-work alloys
The present work aims to reveal the microstructural evolution and post-processing mechanical behavior of difficult-to-work alloys upon severe plastic deformation. Severe plastic deformation is applied using equal channel angular extrusion (ECAE) where billets are pressed through a 90o corner die achieving simple shear deformation. Three different materials are studied in this research, namely Ti-6Al-4V, Ti-6Al-4V reinforced with 10% TiC and AISI 316L stainless steel. Microstructure and mechanical properties of successfully extruded billets were reported using light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), tension and compression experiments and microhardness measurements. The effects of extrusion conditions (temperature and processing route) on the microstructure and mechanical properties are investigated. The underlying mechanisms responsible for observed mechanical behaviors are explored. It is seen that ECAE shear deformation leads to refinement in α plates and elimination of prior β boundaries in Ti-6Al-4V. Decreasing extrusion temperature and increasing number of passes decreases α plate size and grain size. Refined α grain size leads to a significant increase in tensile and compressive flow stresses at room temperature. Texture produced by ECAE has a pronounced effect on mechanical properties. Specifically it leads to tension/compression asymmetry in flow strengths and strain hardening coefficients may be described by the activation of differing slip systems under tension and compression loading. ECAE of Ti-6Al-4V+10%TiC samples also improved mechanical properties due to α plate size refinement. Nevertheless, further extrusion passes should be carried out for tailoring reinforcement size and distribution providing optimum strength and ductility. ECAE deformation of AISI 316L stainless steel at high homologous temperatures (0.55 to 0.60 Tm) results in deformation twinning as an effective deformation mechanism which is attributed to the effect of the high stress levels on the partial dislocation separation. Deformation twinning gives rise to high stress levels during post-processing room temperature tension and compression experiments by providing additional barriers to dislocation motion and decreasing the mean free path of dislocations. The highest tensile flow stress observed in the sample processed at 700 oC following one pass route A was on the order of 1200 MPa which is very high for 316L stainless steel. The ultimate goal of this study is to produce stabilized end microstructures with improved mechanical properties and demonstrate the applicability of ECAE on difficult-to-work alloys
Plant Seed Identification
Plant seed identification is routinely performed for seed certification in seed trade, phytosanitary certification for the import and export of agricultural commodities, and regulatory monitoring, surveillance, and enforcement. Current identification is performed manually by seed analysts with limited aiding tools. Extensive expertise and time is required, especially for small, morphologically similar seeds. Computers are, however, especially good at recognizing subtle differences that humans find difficult to perceive. In this thesis, a 2D, image-based computer-assisted approach is proposed.
The size of plant seeds is extremely small compared with daily objects. The microscopic images of plant seeds are usually degraded by defocus blur due to the high magnification of the imaging equipment. It is necessary and beneficial to differentiate the in-focus and blurred regions given that only sharp regions carry distinctive information usually for identification. If the object of interest, the plant seed in this case, is in- focus under a single image frame, the amount of defocus blur can be employed as a cue to separate the object and the cluttered background. If the defocus blur is too strong to obscure the object itself, sharp regions of multiple image frames acquired at different focal distance can be merged together to make an all-in-focus image. This thesis describes a novel non-reference sharpness metric which exploits the distribution difference of uniform LBP patterns in blurred and non-blurred image regions. It runs in realtime on a single core cpu and responses much better on low contrast sharp regions than the competitor metrics. Its benefits are shown both in defocus segmentation and focal stacking.
With the obtained all-in-focus seed image, a scale-wise pooling method is proposed to construct its feature representation. Since the imaging settings in lab testing are well constrained, the seed objects in the acquired image can be assumed to have measureable scale and controllable scale variance. The proposed method utilizes real pixel scale information and allows for accurate comparison of seeds across scales. By cross-validation on our high quality seed image dataset, better identification rate (95%) was achieved compared with pre- trained convolutional-neural-network-based models (93.6%). It offers an alternative method for image based identification with all-in-focus object images of limited scale variance.
The very first digital seed identification tool of its kind was built and deployed for test in the seed laboratory of Canadian food inspection agency (CFIA). The proposed focal stacking algorithm was employed to create all-in-focus images, whereas scale-wise pooling feature representation was used as the image signature. Throughput, workload, and identification rate were evaluated and seed analysts reported significantly lower mental demand (p = 0.00245) when using the provided tool compared with manual identification. Although the identification rate in practical test is only around 50%, I have demonstrated common mistakes that have been made in the imaging process and possible ways to deploy the tool to improve the recognition rate
Vector Graphics for Real-time 3D Rendering
Algorithms are presented that enable the use of vector graphics representations
of images in texture maps for 3D real time rendering.
Vector graphics images are resolution independent and
can be zoomed arbitrarily without losing detail
or crispness. Many important types of images, including text and
other symbolic information, are best represented in vector form. Vector
graphics textures can also be used as transparency mattes to augment
geometric detail in models via trim curves.
Spline curves are used to represent boundaries around regions
in standard vector graphics representations, such as PDF and SVG.
Antialiased rendering of such content can be obtained by thresholding
implicit representations of these curves.
The distance function is an especially useful implicit representation.
Accurate distance function computations would also allow the implementation
of special effects such as embossing.
Unfortunately, computing the true distance to higher order spline curves
is too expensive for real time rendering.
Therefore, normally either the distance is approximated
by normalizing some other implicit representation
or the spline curves are approximated with simpler primitives.
In this thesis, three methods for
rendering vector graphics textures in real time are introduced,
based on various approximations of the distance computation.
The first and simplest approach to the distance computation
approximates curves with line segments.
Unfortunately, approximation with line segments gives only C0 continuity.
In order to improve smoothness, spline curves can also be approximated
with circular arcs.
This approximation has C1 continuity and computing the distance
to a circular arc is only slightly more expensive than
computing the distance to a line segment.
Finally an iterative algorithm
is discussed that has good performance in practice and can compute the
distance to any parametrically differentiable curve
(including polynomial splines of any order)
robustly. This algorithm is demonstrated in the context of a system
capable of real-time rendering of SVG content in a texture map on a GPU.
Data structures and acceleration algorithms in the context of massively
parallel GPU architectures are also discussed.
These data structures and acceleration structures allow arbitrary vector
content (with space-variant complexity, and overlapping regions) to be
represented in a random-access texture
Fast self-shadowing using occluder textures
A real-time self-shadowing technique is described. State of the art shadowing techniques that utilize
modern hardware often require multiple rendering passes and introduce rendering artifacts. Combining
separate ideas from earlier techniques which project geometry onto a plane and project imagery onto an
object results in a new real-time technique for self-shadowing. This technique allows an artist to construct
occluder textures and assign them to shadow planes for a self-shadowed model. Utilizing a graphics
processing unit (GPU), a vertex program computes shadowing coordinates in real-time, while a fragment
program applies the shading and shadowing in a single rendering pass. The methodology used to create
shadow planes and write the vertex and fragment programs is given, as well as the relation to the previous
work. This work includes implementing this technique, applying it to a small set of test models, describing
the types of models for which the technique is well suited, as well as those for which it is not well suited,
and comparing the techniqueâÂÂs performance and image quality to other state of the art shadowing
techniques. This technique performs as well as other real-time techniques and can reduce rendering
artifacts in certain circumstances
Microstructural Evolution in Friction Stir Welding of Ti-5111
Titanium and titanium alloys have shown excellent mechanical, physical, and corrosion properties. To address the needs of future naval combatants, this research examines an alternative joining technology, friction stir welding (FSW). Friction stir welding uses a non-consumable tool to generate frictional heat to plastically deform and mix metal to form a consolidated joint. This work focuses on FSW of Ti-5111 (Ti-5Al-1Sn-1Zr-1V-0.8Mo), a near alpha alloy. This study aims to gain a fundamental understanding of the relationship between processing parameters, microstructure, and mechanical properties of experimental 12.7mm and 6.35mm Ti-5111 friction stir welds.
The resulting weld microstructure shows significant grain refinement within the weld compared to the base metal. The weld microstructures show a fully lamellar colony structure with peak welding temperatures exceeding beta transformation temperature. The friction stir weld shows material texture strengthening of the BCC F fiber component before transformation to D2 shear texture in the stir zone. Transmission electron microscopy results of the base metal and the stir zone show a lath colony-type structure with low dislocation density and no lath grain substructure. In situ TEM heating experiments of Ti-5111 friction stir welded material show transformation to the high temperature beta phase at significantly lower temperatures compared to the base metal.
Thermal and deformation mechanisms within Ti-5111 were examined through the use of thermomechanical simulation. Isothermal constant strain rate tests show evidence of dynamic recrystallization and deformation above beta transus when compared with the FSW thermal profile without deformation. Subtransus deformation shows kinking and bending of the existing colony structure without recrystallization. Applying the friction stir thermal profile to constant strain rate deformation successfully reproduced the friction stir microstructure at a peak temperature of 1000ºC and a strain rate of 10/s. These results provide unique insight into the strain, strain rates, and temperatures regime within the process.
Finally, the experimental thermal and deformation fields were compared using ISAIAH, a Eulerian based three-dimensional model of friction stir welding. These results are preliminary but show promise for the ability of the model to compute thermal fields for material flow, model damage prediction, and decouple texture evolution for specific thermomechanical histories in the friction stir process
Haptic Interaction with 3D oriented point clouds on the GPU
Real-time point-based rendering and interaction with virtual objects is gaining popularity
and importance as di�erent haptic devices and technologies increasingly provide the basis
for realistic interaction. Haptic Interaction is being used for a wide range of applications
such as medical training, remote robot operators, tactile displays and video games. Virtual
object visualization and interaction using haptic devices is the main focus; this process
involves several steps such as: Data Acquisition, Graphic Rendering, Haptic Interaction
and Data Modi�cation. This work presents a framework for Haptic Interaction using the
GPU as a hardware accelerator, and includes an approach for enabling the modi�cation
of data during interaction. The results demonstrate the limits and capabilities of these
techniques in the context of volume rendering for haptic applications. Also, the use
of dynamic parallelism as a technique to scale the number of threads needed from the
accelerator according to the interaction requirements is studied allowing the editing of
data sets of up to one million points at interactive haptic frame rates
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