Proceedings of the 22nd annual conference on Computer graphics and interactive techniques - SIGGRAPH '95, 1995
Developing a visually convincing model of fire, smoke, and other gaseous phenomena is among the m... more Developing a visually convincing model of fire, smoke, and other gaseous phenomena is among the most difficult and attractive problems in computer graphics. We have created new methods of animating a wide range of gaseous phenomena, including the particularly subtle problem of modelling "wispy" smoke and steam, using far fewer primitives than before. One significant innovation is the reformulation and solution of the advection-diffusion equation for densities composed of "warped blobs". These blobs more accurately model the distortions that gases undergo when advected by wind fields. We also introduce a simple model for the flame of a fire and its spread. Lastly, we present an efficient formulation and implementation of global illumination in the presence of gases and fire. Our models are specifically designed to permit a significant degree of user control over the evolution of gaseous phenomena.
. In this paper, we explore the theory of optical deformations due to continuous variations of th... more . In this paper, we explore the theory of optical deformations due to continuous variations of the refractive index of the air, and present several efficient implementations. We introduce the basic equations from geometrical optics, outlining a general method of solution. Further, we model the fluctuations of the index of refraction both as a superposition of blobs and as a stochastic function. Using a well known perturbation technique from geometrical optics, we compute linear approximations to the deformed rays. We employ this approximation and the blob representation to efficiently ray trace non linear rays through multiple environments. In addition we present a stochastic model for the ray deviations derived from an empirical model of air turbulence. We use this stochastic model to precompute deformation maps. 1
Stochastic modelling has been successfully used in computer graphics to model a wide array of nat... more Stochastic modelling has been successfully used in computer graphics to model a wide array of natural phenomena. In modelling three-dimensional fuzzy or partially translucent phenomena, however, many approaches are hampered by high memory and computation requirements, and by a general lack of user control. We will present a general stochastic modelling primitive that operates on two or more scales of visual detail, and which offers considerable flexibility and control of the model. At the macroscopic level, the general shape of the model is constrained by an ellipsoidal correlation function that controls the interpolation of user-supplied data values. We use a technique called Kriging to perform this interpolation. The microscopic level permits the addition of noise, which allows a user to add interesting visual textural detail and translucency. A wide variety of noisesynthesis techniques can be employed in our model. We shall describe the mathematical structure of our model, and gi...
This paper presents a new animation framework for the modeling of gaseous phenomena. We combine p... more This paper presents a new animation framework for the modeling of gaseous phenomena. We combine particle and grid based techniques in an innovative way. Based on this framework, our system allows for an incremental design of animations. In the first stage, an animator uses particle methods to model the evolution and appearance of gases. Grid based techniques are subsequently employed to compute high quality animations. Central to the success of our technique is a new algorithm to efficiently advect densities on grids. To demonstrate the effectiveness of our approach, we have included many animations. Key Words & Phrases: Animation, Modeling and Rendering of Gaseous Phenomena, Turbulence, Advection of Densities, Volume Rendering. _______________________________________________________________________ Supported by an ERCIM (European Research Consortium for Informatics and Mathematics) Fellowship. This work was done while the author was visiting VTT from July 1996 to March 1997. 2 1.
Proceedings of the 28th annual conference on Computer graphics and interactive techniques - SIGGRAPH '01, 2001
In this paper, we propose a new approach to numerical smoke simulation for computer graphics appl... more In this paper, we propose a new approach to numerical smoke simulation for computer graphics applications. The method proposed here exploits physics unique to smoke in order to design a numerical method that is both fast and efficient on the relatively coarse grids traditionally used in computer graphics applications (as compared to the much finer grids used in the computational fluid dynamics literature). We use the inviscid Euler equations in our model, since they are usually more appropriate for gas modeling and less computationally intensive than the viscous Navier-Stokes equations used by others. In addition, we introduce a physically consistent vorticity confinement term to model the small scale rolling features characteristic of smoke that are absent on most coarse grid simulations. Our model also correctly handles the interaction of smoke with moving objects.
Proceedings of the 20th annual conference on Computer graphics and interactive techniques - SIGGRAPH '93, 1993
The realistic depiction of smoke, steam, mist and water reacting to a turbulent eld such as wind ... more The realistic depiction of smoke, steam, mist and water reacting to a turbulent eld such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent elds, gaseous ow, and realistic illumination. We present a model for turbulent wind ow having a deterministic component to specify large-scale behaviour, and a stochastic component to model turbulent small-scale behaviour. The small-scale component is generated using space-time Fourier synthesis. Turbulent wind elds can be superposed interactively to create subtle behaviour. An advection-di usion model is used to animate particle-based gaseous phenomena embedded in a wind eld, and we derive an e cient physically-based illumination model for rendering the system. Because the number of particles can be quite large, we present a clustering algorithm for e cient animation and rendering.
Proceedings of the 2005 symposium on Interactive 3D graphics and games - SI3D '05, 2005
We describe a new interaction technique, called HoverCam, for navigating around 3D objects at clo... more We describe a new interaction technique, called HoverCam, for navigating around 3D objects at close proximity. When a user is closely inspecting an object, the camera motions needed to move across its surface can become complex. For tasks such as 3D painting or modeling small detail features, users will often try to keep the camera a small distance above the surface. To achieve this automatically, HoverCam intelligently integrates tumbling, panning, and zooming camera controls into a single operation. This allows the user to focus on the task at hand instead of continuously managing the camera position and orientation. In this paper we show unique affordances of the technique and define the behavior and implementation of HoverCam. We also show how the technique can be used for navigating about data sets without well-defined surfaces such as point clouds and curves in space.
Proceedings of the conference on SIGGRAPH 2004 course notes - GRAPH '04, 2004
This updated course on simulating natural phenomena will cover the latest research and production... more This updated course on simulating natural phenomena will cover the latest research and production techniques for simulating most of the elements of nature. The presenters will provide movie production, interactive simulation, and research perspectives on the difficult task of photorealistic modeling, rendering, and animation of natural phenomena. The course offers a nice balance of the latest interactive graphics hardware-based simulation
Pontine hyperintense lesions (PHL) on T2-weighted MRI have been recognized recently. Histopatholo... more Pontine hyperintense lesions (PHL) on T2-weighted MRI have been recognized recently. Histopathological findings resemble periventricular leukoaraiosis, and a vascular etiology has been suggested. We studied the frequency and the associated factors of PHL in patients with symptomatic atherosclerosis. Two independent observers assessed brain MRIs in a prospective cohort of patients with symptomatic atherosclerosis. Only patients in whom both observers scored PHL on T2- and proton density-weighted images, but not on T1-weighted images, were considered to have the lesion. We studied 229 patients 31% presenting with ischemic stroke, 31% with myocardial infarction, and 38% with peripheral artery disease. Both observers scored PHL in 23% of all patients. Patients with PHL were significantly older and had more lacunar infarcts and periventricular leukoaraiosis than patients without PHL. There were more women, more hypercholesterolemic and diabetic patients, and more cortical infarcts on MRI (P = NS). After logistic regression the presence of leukoaraiosis (odds ratio, 2.4; 95% confidence interval, 1.6 to 3.4) and lacunar infarcts (odds ratio, 2.2, 95% confidence interval, 1.5 to 3.1) remained independently associated with PHL. PHL was more common in patients with ischemic strokes (39%) than in patients with myocardial infarctions (11%) or peripheral artery disease (19%) (P < .001). We found that PHL on T2- and proton density-weighted MR images are often found in patients with symptomatic atherosclerosis. The association with periventricular leukoaraiosis and lacunar infarcts suggests that PHL is a variant of leukoaraiosis, with possibly the same pathophysiology. The clinical symptoms and consequences of PHL, however, are not yet clear.
Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal mes... more Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal meshes. In this paper we propose to employ subdivision rules as a polygonal modeling tool, specifically to add additional level of detail to meshes. However, existing subdivision schemes have several undesirable properties making them ill suited for polygonal modeling. In this paper we propose a general set of subdivision rules which provides users with more control over the subdivision process. Most existing subdivision schemes are special cases. In particular, we provide subdivision rules which blend approximating spline based schemes with interpolatory ones. Also, we generalize subdivision to allow any number of refinements to be performed in a single step.
In this paper we introduce a new subdivision operator that unifies triangular and quadrilateral s... more In this paper we introduce a new subdivision operator that unifies triangular and quadrilateral subdivision schemes. Designers often want the added flexibility of having both quads and triangles in their models. It is also well known that triangle meshes generate poor limit surfaces when using a quad scheme, while quad-only meshes behave poorly with triangular schemes. Our new scheme is a generalization of the well known Catmull-Clark and Loop subdivision algorithms. We show that our surfaces are C 1 everywhere and provide a proof that it is impossible to construct a C 2 scheme at the quad/triangle boundary. However, we provide rules that produce surfaces with bounded curvature at the regular quad/triangle boundary and provide optimal masks that minimize the curvature divergence elsewhere. We demonstrate the visual quality of our surfaces with several examples.
We introduce a new class of subdivision surfaces which generalize uniform tensor product B-spline... more We introduce a new class of subdivision surfaces which generalize uniform tensor product B-spline surfaces of any bi-degree to meshes of arbitrary topology. Surprisingly, this can be done using subdivision rules that involve direct neighbors only. Consequently, our schemes are very easy to implement, regardless of degree. The famous Catmull-Clark scheme is a special case. Similarly we show that triangular box splines of total degree 3m + 1 can be generalized to arbitrary triangulations.
During periods of droughts the National Coordinating Committee for Water Distribution of the Neth... more During periods of droughts the National Coordinating Committee for Water Distribution of the Netherlands has to decide how the available surface water is used and allocated between different users (agriculture, navigation, industry etc). To support this decision making, real-time information is needed about the availability of surface water, groundwater levels, saturation of the root zone, etc. This real-time information must
Abstract: We present a physics-based generative design approach to interactive form-finding. Whil... more Abstract: We present a physics-based generative design approach to interactive form-finding. While form as a product of dynamic simulation has been explored previously, individual projects have been developed as singleton solutions. By identifying categories of ...
In this paper we derive an equation for the velocity of an arbitrary timeevolving implicit surfac... more In this paper we derive an equation for the velocity of an arbitrary timeevolving implicit surface. Strictly speaking only the normal component of the velocity is unambiguously defined. This is because an implicit surface does not have a unique parametrization. However, by enforcing a constraint on the evolution of the normal field we obtain a unique tangential component. We apply our formulas to surface tracking and to the problem of computing velocity vectors of a motion blurred blobby surface. Other possible applications are mentioned at the end of the paper.
Proceedings of the 22nd annual conference on Computer graphics and interactive techniques - SIGGRAPH '95, 1995
Developing a visually convincing model of fire, smoke, and other gaseous phenomena is among the m... more Developing a visually convincing model of fire, smoke, and other gaseous phenomena is among the most difficult and attractive problems in computer graphics. We have created new methods of animating a wide range of gaseous phenomena, including the particularly subtle problem of modelling "wispy" smoke and steam, using far fewer primitives than before. One significant innovation is the reformulation and solution of the advection-diffusion equation for densities composed of "warped blobs". These blobs more accurately model the distortions that gases undergo when advected by wind fields. We also introduce a simple model for the flame of a fire and its spread. Lastly, we present an efficient formulation and implementation of global illumination in the presence of gases and fire. Our models are specifically designed to permit a significant degree of user control over the evolution of gaseous phenomena.
. In this paper, we explore the theory of optical deformations due to continuous variations of th... more . In this paper, we explore the theory of optical deformations due to continuous variations of the refractive index of the air, and present several efficient implementations. We introduce the basic equations from geometrical optics, outlining a general method of solution. Further, we model the fluctuations of the index of refraction both as a superposition of blobs and as a stochastic function. Using a well known perturbation technique from geometrical optics, we compute linear approximations to the deformed rays. We employ this approximation and the blob representation to efficiently ray trace non linear rays through multiple environments. In addition we present a stochastic model for the ray deviations derived from an empirical model of air turbulence. We use this stochastic model to precompute deformation maps. 1
Stochastic modelling has been successfully used in computer graphics to model a wide array of nat... more Stochastic modelling has been successfully used in computer graphics to model a wide array of natural phenomena. In modelling three-dimensional fuzzy or partially translucent phenomena, however, many approaches are hampered by high memory and computation requirements, and by a general lack of user control. We will present a general stochastic modelling primitive that operates on two or more scales of visual detail, and which offers considerable flexibility and control of the model. At the macroscopic level, the general shape of the model is constrained by an ellipsoidal correlation function that controls the interpolation of user-supplied data values. We use a technique called Kriging to perform this interpolation. The microscopic level permits the addition of noise, which allows a user to add interesting visual textural detail and translucency. A wide variety of noisesynthesis techniques can be employed in our model. We shall describe the mathematical structure of our model, and gi...
This paper presents a new animation framework for the modeling of gaseous phenomena. We combine p... more This paper presents a new animation framework for the modeling of gaseous phenomena. We combine particle and grid based techniques in an innovative way. Based on this framework, our system allows for an incremental design of animations. In the first stage, an animator uses particle methods to model the evolution and appearance of gases. Grid based techniques are subsequently employed to compute high quality animations. Central to the success of our technique is a new algorithm to efficiently advect densities on grids. To demonstrate the effectiveness of our approach, we have included many animations. Key Words & Phrases: Animation, Modeling and Rendering of Gaseous Phenomena, Turbulence, Advection of Densities, Volume Rendering. _______________________________________________________________________ Supported by an ERCIM (European Research Consortium for Informatics and Mathematics) Fellowship. This work was done while the author was visiting VTT from July 1996 to March 1997. 2 1.
Proceedings of the 28th annual conference on Computer graphics and interactive techniques - SIGGRAPH '01, 2001
In this paper, we propose a new approach to numerical smoke simulation for computer graphics appl... more In this paper, we propose a new approach to numerical smoke simulation for computer graphics applications. The method proposed here exploits physics unique to smoke in order to design a numerical method that is both fast and efficient on the relatively coarse grids traditionally used in computer graphics applications (as compared to the much finer grids used in the computational fluid dynamics literature). We use the inviscid Euler equations in our model, since they are usually more appropriate for gas modeling and less computationally intensive than the viscous Navier-Stokes equations used by others. In addition, we introduce a physically consistent vorticity confinement term to model the small scale rolling features characteristic of smoke that are absent on most coarse grid simulations. Our model also correctly handles the interaction of smoke with moving objects.
Proceedings of the 20th annual conference on Computer graphics and interactive techniques - SIGGRAPH '93, 1993
The realistic depiction of smoke, steam, mist and water reacting to a turbulent eld such as wind ... more The realistic depiction of smoke, steam, mist and water reacting to a turbulent eld such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent elds, gaseous ow, and realistic illumination. We present a model for turbulent wind ow having a deterministic component to specify large-scale behaviour, and a stochastic component to model turbulent small-scale behaviour. The small-scale component is generated using space-time Fourier synthesis. Turbulent wind elds can be superposed interactively to create subtle behaviour. An advection-di usion model is used to animate particle-based gaseous phenomena embedded in a wind eld, and we derive an e cient physically-based illumination model for rendering the system. Because the number of particles can be quite large, we present a clustering algorithm for e cient animation and rendering.
Proceedings of the 2005 symposium on Interactive 3D graphics and games - SI3D '05, 2005
We describe a new interaction technique, called HoverCam, for navigating around 3D objects at clo... more We describe a new interaction technique, called HoverCam, for navigating around 3D objects at close proximity. When a user is closely inspecting an object, the camera motions needed to move across its surface can become complex. For tasks such as 3D painting or modeling small detail features, users will often try to keep the camera a small distance above the surface. To achieve this automatically, HoverCam intelligently integrates tumbling, panning, and zooming camera controls into a single operation. This allows the user to focus on the task at hand instead of continuously managing the camera position and orientation. In this paper we show unique affordances of the technique and define the behavior and implementation of HoverCam. We also show how the technique can be used for navigating about data sets without well-defined surfaces such as point clouds and curves in space.
Proceedings of the conference on SIGGRAPH 2004 course notes - GRAPH '04, 2004
This updated course on simulating natural phenomena will cover the latest research and production... more This updated course on simulating natural phenomena will cover the latest research and production techniques for simulating most of the elements of nature. The presenters will provide movie production, interactive simulation, and research perspectives on the difficult task of photorealistic modeling, rendering, and animation of natural phenomena. The course offers a nice balance of the latest interactive graphics hardware-based simulation
Pontine hyperintense lesions (PHL) on T2-weighted MRI have been recognized recently. Histopatholo... more Pontine hyperintense lesions (PHL) on T2-weighted MRI have been recognized recently. Histopathological findings resemble periventricular leukoaraiosis, and a vascular etiology has been suggested. We studied the frequency and the associated factors of PHL in patients with symptomatic atherosclerosis. Two independent observers assessed brain MRIs in a prospective cohort of patients with symptomatic atherosclerosis. Only patients in whom both observers scored PHL on T2- and proton density-weighted images, but not on T1-weighted images, were considered to have the lesion. We studied 229 patients 31% presenting with ischemic stroke, 31% with myocardial infarction, and 38% with peripheral artery disease. Both observers scored PHL in 23% of all patients. Patients with PHL were significantly older and had more lacunar infarcts and periventricular leukoaraiosis than patients without PHL. There were more women, more hypercholesterolemic and diabetic patients, and more cortical infarcts on MRI (P = NS). After logistic regression the presence of leukoaraiosis (odds ratio, 2.4; 95% confidence interval, 1.6 to 3.4) and lacunar infarcts (odds ratio, 2.2, 95% confidence interval, 1.5 to 3.1) remained independently associated with PHL. PHL was more common in patients with ischemic strokes (39%) than in patients with myocardial infarctions (11%) or peripheral artery disease (19%) (P < .001). We found that PHL on T2- and proton density-weighted MR images are often found in patients with symptomatic atherosclerosis. The association with periventricular leukoaraiosis and lacunar infarcts suggests that PHL is a variant of leukoaraiosis, with possibly the same pathophysiology. The clinical symptoms and consequences of PHL, however, are not yet clear.
Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal mes... more Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal meshes. In this paper we propose to employ subdivision rules as a polygonal modeling tool, specifically to add additional level of detail to meshes. However, existing subdivision schemes have several undesirable properties making them ill suited for polygonal modeling. In this paper we propose a general set of subdivision rules which provides users with more control over the subdivision process. Most existing subdivision schemes are special cases. In particular, we provide subdivision rules which blend approximating spline based schemes with interpolatory ones. Also, we generalize subdivision to allow any number of refinements to be performed in a single step.
In this paper we introduce a new subdivision operator that unifies triangular and quadrilateral s... more In this paper we introduce a new subdivision operator that unifies triangular and quadrilateral subdivision schemes. Designers often want the added flexibility of having both quads and triangles in their models. It is also well known that triangle meshes generate poor limit surfaces when using a quad scheme, while quad-only meshes behave poorly with triangular schemes. Our new scheme is a generalization of the well known Catmull-Clark and Loop subdivision algorithms. We show that our surfaces are C 1 everywhere and provide a proof that it is impossible to construct a C 2 scheme at the quad/triangle boundary. However, we provide rules that produce surfaces with bounded curvature at the regular quad/triangle boundary and provide optimal masks that minimize the curvature divergence elsewhere. We demonstrate the visual quality of our surfaces with several examples.
We introduce a new class of subdivision surfaces which generalize uniform tensor product B-spline... more We introduce a new class of subdivision surfaces which generalize uniform tensor product B-spline surfaces of any bi-degree to meshes of arbitrary topology. Surprisingly, this can be done using subdivision rules that involve direct neighbors only. Consequently, our schemes are very easy to implement, regardless of degree. The famous Catmull-Clark scheme is a special case. Similarly we show that triangular box splines of total degree 3m + 1 can be generalized to arbitrary triangulations.
During periods of droughts the National Coordinating Committee for Water Distribution of the Neth... more During periods of droughts the National Coordinating Committee for Water Distribution of the Netherlands has to decide how the available surface water is used and allocated between different users (agriculture, navigation, industry etc). To support this decision making, real-time information is needed about the availability of surface water, groundwater levels, saturation of the root zone, etc. This real-time information must
Abstract: We present a physics-based generative design approach to interactive form-finding. Whil... more Abstract: We present a physics-based generative design approach to interactive form-finding. While form as a product of dynamic simulation has been explored previously, individual projects have been developed as singleton solutions. By identifying categories of ...
In this paper we derive an equation for the velocity of an arbitrary timeevolving implicit surfac... more In this paper we derive an equation for the velocity of an arbitrary timeevolving implicit surface. Strictly speaking only the normal component of the velocity is unambiguously defined. This is because an implicit surface does not have a unique parametrization. However, by enforcing a constraint on the evolution of the normal field we obtain a unique tangential component. We apply our formulas to surface tracking and to the problem of computing velocity vectors of a motion blurred blobby surface. Other possible applications are mentioned at the end of the paper.
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