Query: sphere tracing

title: DIST: Rendering Deep Implicit Signed Distance Function With Differentiable Sphere Tracing
abstract: We propose a differentiable sphere tracing algorithm to bridge the gap between inverse graphics methods and the recently proposed deep learning based implicit signed distance function. Due to the nature of the implicit function, the rendering process requires tremendous function queries, which is particularly problematic when the function is represented as a neural network. We optimize both the forward and backward pass of our rendering layer to make it run efficiently with affordable memory consumption on a commodity graphics card. Our rendering method is fully differentiable such that losses can be directly computed on the rendered 2D observations, and the gradients can be propagated backward to optimize the 3D geometry. We show that our rendering method can effectively reconstruct accurate 3D shapes from various inputs, such as sparse depth and multi view images, through inverse optimization. With the geometry based reasoning, our 3D shape prediction methods show excellent generalization capability and robustness against various noises.

title: Non linear sphere tracing for rendering deformed signed distance fields
abstract: Signed distance fields (SDFs) are a powerful implicit representation for modeling solids, volumes and surfaces. Their infinite resolution, controllable continuity and robust constructive solid geometry operations, coupled with smooth blending, enable powerful and intuitive sculpting tools for creating complex SDF models. SDF metric properties also admit efficient surface rendering with sphere tracing. Unfortunately, SDFs remain incompatible with many popular direct deformation techniques which re position a surface via its explicit representation. Linear blend skinning used in character articulation, for example, directly displaces each vertex of a triangle mesh. To overcome this limitation, we propose a variant of sphere tracing for directly rendering deformed SDFs. We show that this problem reduces to integrating a non linear ordinary differential equation. We propose an efficient numerical solution, with controllable error, which first automatically computes an initial value along each cast ray before walking conservatively along a curved ray in the undeformed space according to the signed distance. Importantly, our approach does not require knowledge, computation or even global existence of the inverse deformation, which allows us to readily apply many existing forward deformations. We demonstrate our method's effectiveness for interactive rendering of a variety of popular deformation techniques that were, to date, limited to explicit surfaces.

title: Non linear sphere tracing for rendering deformed signed distance fields
abstract: Signed distance fields (SDFs) are a powerful implicit representation for modeling solids, volumes and surfaces. Their infinite resolution, controllable continuity and robust constructive solid geom.

title: Accelerating Sphere Tracing

title: Sphere Tracing GPU An evaluation of the Sphere Tracing algorithm and a GPU designed to run it
abstract: This thesis documents our experiences and conclusions during the design of a graphics processing unit (GPU) specifically designed and optimized for executing the Sphere Tracing algorithm, which is a variation of the standard Ray Tracing algorithm. The GPU is written in the functional hardware description language CaSH. A shader was also implemented in GLSL to enable algorithm research. Real time rendering performance has always been a significant factor for 3D graphics cards. However, using the Sphere Tracing algorithm on conventional 3D graphics cards is slow because they are designed and built for polygon based rendering. We assessed potential performance improvements using our GLSL shader. The results indicate that it is possible to increase the performance of the Sphere Tracing algorithm.

title: Enhanced Sphere Tracing
abstract: In this paper we present several performance and quality enhancements to classical sphere tracing: First, we propose a safe, over relaxation based method for accelerating sphere tracing. Second, a method for dynamically preventing self intersections upon converting signed distance bounds enables controlling precision and rendering performance. In addition, we present a method for significantly accelerating the sphere tracing intersection test for convex objects that are enclosed in convex bounding volumes. We also propose a screen space metric for the retrieval of a good intersection point candidate, in case sphere tracing does not converge thus increasing rendering quality without sacrificing performance. Finally, discontinuity artifacts common in sphere tracing are reduced using a fixed point iteration algorithm. We demonstrate complex scenes rendered in real time with our method. The methods presented in this paper have more universal applicability beyond rendering procedurally generated scenes in real time and can also be combined with path tracing based global illumination solutions.

title: GPU Based Sphere Tracing for Radial Basis Function Implicits
abstract: Ray tracing of implicit surfaces based on radial basis functions can demand high computational cost in the presence of a large number of radial centers. Recently, it was presented the least squares hermite radial basis functions (LS HRBF) Implicits, a method for implicit surface reconstruction from Hermitian data (points equipped with their normal vectors) which makes use of iterative center selection in order to reduce the number of centers. In the present work, we propose an antialiazed sphere tracing algorithm fully implemented in OpenGL Shader Language for ray tracing LS HRBF Implicits, which exploits a regular partition of unity for strong parallelization. We show that interactive frame rates can be achieved for surfaces composed of thousands of centers even when rendering effects such as cube mapping, soft shadows and ambient occlusion are used.

title: Real Time Audio Simulation with Implicit Surfaces using Sphere Tracing on the GPU
abstract: Digital games are based on interactive virtual environments where graphics and audio are combined. In many of these games there is lot of effort put into graphics while leaving the audio part underdeveloped. Audio in games is important in order to immerse the player in the virtual environment. Where a high level of emulated reality is needed graphics and audio should be combined on a similar level of realism. To make this possible a sophisticated method for audio simulation is needed. In the audio simulation field previous attempts at using ray tracing methods were successful. With methods based on ray tracing the sound waves are traced from the audio source to the listener in the virtual environment, where the environment is based on a scene consisting of implicit surfaces. A key part in the tracing computations is finding the intersection point between a sound wave and the surfaces in the scene. Sphere tracing is an alternative method for finding the intersection point and has been shown to be feasible for real time usage on the graphics processing unit (GPU) To be interactive a game environment runs in real time, this fact puts a time constraint on the rendering of the graphics and audio. The time constraint is based on the time window to render one frame in the synchronized rendering of graphics and audio based on the frame rate of the graphics. Consumer computer systems of today are in general equipped with a GPU, if an audio simulation can use the GPU in real time this is a possible implementation target in a game system. The aim of this thesis is to investigate if audio simulation with the ray tracing method based on sphere tracing is possible to run in real time on the GPU. An audio simulation system is implemented in order to examine the possibility for real time usage based on computation time. The results of this thesis show that audio simulation with implicit surfaces using sphere tracing is possible to use in real time with the GPU in some form. The time consumption for an audio simulation system like this is small enough to enable it for real time usage. Based on an interactive graphics frame rate the time consumption allows the graphics and audio computations to use the GPU in the same frame time.

title: Tracing the shear modulus of blood plasma during clotting and based on acoustic radiation force induced vibration of an embedded sphere
abstract: During coagulation, blood changes from liquid to gel, and the clot viscoelastic properties continue modifying until fibrinolysis. Ultrasound (US) was used in this work to trace the time changing shear modulus, m, during plasma clotting, based on the vibration signature induced by an impulsive acoustic radiation force (iARF) on a sphere embedded in a plasma sample along its clotting process induced based on the aPTT (activated partial thromboplastin time) assay. An US push system transmitted bursts of US pulses (2.03 MHz, 1000 cycles and 1.25 Hz of pulse repetition frequency) to generate an iARF on the glass sphere (4.0 mm in diameter and density of 2500 kg/m3) which displacement was monitored by a 5.0 MHz US pulse echo probing system. The relative delays between the rf echo signals from the sphere yielded the signal representing the sphere damped oscillation that was fitted with a theoretical model displacement function whose unknowns are the iARF amplitude and the medium m and shear viscosity, e. The method was repeated five times and the time changing mean m was determined along 2100 s of the clotting process. During the first 15 s m remained at 20 Pa and then varied rapidly until 60 s, at a rate of 1.9 Pa/s. Between 60 and 800 s, m varied at a rate of 0.2 Pa/s. From 800 to 2100 s m remained stable at about 280 Pa. The interval of fast changing m corresponds to the fibrin formation period and comprehends the clotting time of 25s typically obtained with the aPTT assay for control plasma.

title: Sphere Tracing: Simple Robust Antialiased Rendering of Distance Based Implicit Surfaces
abstract: Sphere tracing is a new numerical method for nd ing the intersection of a ray with an implicit surface. Unlike Newton's method or regula falsi, it is robust, converging if and only if the ray intersects the implicit surface, and it converges on the rst intersection the intersection closest to the ray origin. It is signiicantly simpler to implement than other robust intersection techniques, such as interval analysis or LG surfaces. Sphere tracing beneets from implicit surfaces that return distance, but requires only the imposition of the Lipschitz condition on implicit functions, and so has a wide application base. Sphere tracing also reduces to cone tracing, producing antialiased renderings though casting only one ray through each pixel. Appropriate distance functions are derived for solid modeling primitives, CSG operations, two blends, and several deformations. Finally resulting sphere traced images of blended and deformed implicit surfaces are exhibited.