M. Watt, "Light-Water Interaction using Backward Beam Tracing," Computer Graphics, Vol. 24, No. 4, (1990),pp. 377376.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....(see section 5) In either case, our goal is to compute the caustic surface from the given mapping. When this mapping is known in closed form, analytic methods can be used to derive the caustic surface [4] When a discrete approximation is given, a host of numerical methods [12] 18] [26] , may be used. The method we use computes the caustic by finding all the points where the change in coordinates described above is singular [2] 3] Equation (2) expresses # in terms of a known or measured ray surface #### ##. The caustic is defined as the singularities in the change from ....

M. Watt. Light-water interaction using backward beam tracing. Computer Graphics, 24(4):377--385, 1990.

....[Sta99] all on a 64 64 grid. Light rays going through the vertices of the surface triangles are followed onto the ground, taking into account the refraction according to Snell s law. These triangles are illuminated inversely proportional to their area, comparable to backward beam tracing [Wat90]. Shafts of light, which are important for underwater scenes, are rendered by slicing the volume into layers which are approximated by blending textured planes. Hinsinger, Neyret, and Cani [Hin02] also synthesize Gerstner waves. Their scheme adapts to the visible size of each surface element. ....

....is used on the ground (a large square) and with distorted texture coordinates on the water surface, see section 4. Light Source Water Surface Ground Figure 5. The caustics simulation computes light rays through each vertex by linear approximation. The caustics computation proceeds as in [Wat90]: Light rays are sent from the sun through each vertex on the water and refracted according to the normal vector. Thus, each triangle on the surface is projected down to a distorted triangle on the floor, see Figure 5. The calculation of the 2 D coordinates (x,y) on the floor can be done by linear ....

Watt, M. Light-Water Interaction Using Backward Beam Tracing. Proceedings of SIGGRAPH '90, pp. 377--385, 1990.

....beam is constructed by mirroring the transmission beam over the polygon s plane, and possibly other beams are formed to model other types of scattering. This method has been used in a variety of application areas, including acoustic modeling [25, 37, 38, 39, 85, 110, 129] global illumination [18, 36, 46, 48, 52, 130], radio wave propagation [34, 33] and visibility determination [40, 55, 79, 116] Original Beam Reflection Beam Transmission S S a b c Figure 11: Beam tracing method. As compared to image source methods, the advantage of beam tracing is that fewer virtual sources must be considered ....

Mark Watt. Light-water interaction using backward beam tracing. ACM Computer Graphics, SIGGRAPH '90 Proceedings, pages 377--385, August 1990.

....maps as data structures by using them to accumulate illumination. Heckbert and Hanrahan [9] leveraged the spatial coherence of polygonal objects by reflecting and refracting beams from the visible surfaces in the view frustum, starting at the eye point. The reverse approach was taken up by Watt [26], who calculated the caustics on the bottom of a swimming pool using backward beam tracing. Both Watt s approach [26] and Heckbert and Hanrahan s approach would involve rendering multiple polygons and blending them in order to create the refractive caustic, which would require on the order of n ....

....of polygonal objects by reflecting and refracting beams from the visible surfaces in the view frustum, starting at the eye point. The reverse approach was taken up by Watt [26] who calculated the caustics on the bottom of a swimming pool using backward beam tracing. Both Watt s approach [26] and Heckbert and Hanrahan s approach would involve rendering multiple polygons and blending them in order to create the refractive caustic, which would require on the order of n passes if the surface was composed of n polygons. This is a result of their discretization. In the present paper, we ....

Mark Watt. Light-water interaction using backward beam tracing. Computer Graphics, 24(4):327--335, 1990.

....of the radiance distribution within and leaving a water body is a prerequisite for the solution of many problems in underwater visibility, remote sensing, mixedlayer thermodynamics, and realistic image synthesis. Watt describes a backward beam tracing approach to interaction of light with water [7], but his method does not take into account complex optical properties of water bodies. Nishita and Nakamae presented a method that can effectively calculate optical effects [8] Their method focuses primarily on effects such as caustics and shafts of light in water bodies. In this paper we ....

M. Watt. Light--water interaction using backward beam tracing. In F. Baskett (ed), Computer Graphics (SIGGRAPH '90 Proceedings). volume 24, pages 377--

....Island for which he used several superimposed 1 sinusoidal waves of low amplitude. This approach was significantly developed by Masten[6] with the use of Fourier Synthesis. Kass and Miller[4] took the previous research and added the fluid dynamics component to model shallow water. Similarly, Watt[9] showed how water reflection above and below the surface can be modeled using backward beam tracing. All of this work was done in order to render large bodies of water having no contact with the ground. A few papers had taken into account shoreline and cresting water models: Peachey [8] and ....

Mark Watt. Light-water interaction using backward beam tracing. SIGGRAPH '90 Conference Proceedings, 24(4):377--385, August, 1990.

....the shadow region, a transmission beam is constructed matching the shadow region, and a reflection beam is constructed by mirroring the transmission beam over the polygon s plane. This method has been used in a variety of applications, including acoustic modeling [27, 8, 29, 30, 31] illumination [32, 33, 34, 35, 28, 36], visibility determination [37, 38, 39] and radio propagation prediction [40, 41] The primary advantage of beam tracing is that it leverages geometric coherence, since each beam represents an infinite number of potential ray paths emanating from the source location. It does not suffer from the ....

Mark Watt. Light-water interaction using backward beam tracing. ACM Computer Graphics, SIGGRAPH'90 Proceedings, pages 377--385, August 1990.

....In particular, the creation and rendering of realistic water scenes is one of the challenging tasks in Computer Graphics. Most of the work that has been done is concerned with the effects of the reflection and refraction of light on the water surface: shafts of light, caustics. Shnyi89a] [WattM90a], Nishi94a] Great effort has been taken in studying atmospheric conditions to know how much sunlight and skylight reaches the water surface and the problem of wave generation [Fourn86a] TsoPY87a] Peach86a] However, realistic rendering of water scenes requires the transport of light within ....

Watt, M.: Light-Water Interaction using Backward Beam Tracing, Computer Graphics Vol.24, No. 4, pp.377-385, 1990.

....estimate is less prone to noise since it can be seen as a low pass filter. The photon map does however require large amounts of memory in complex scenes. In scenes with simple objects it is possible to avoid the photon based approach. If the specular objects are polyhedral backwards beam tracing [14, 15, 21] can be used to render caustics on the Lambertian surfaces. With backwards beam tracing the illumination map can be replaced by caustic polygons that represent illumination from caustics on Lambertian surfaces. In bidirectional path tracing [11, 18] the rendering of caustics is significantly ....

Watt, Mark: "Light-Water Interaction using Backward Beam Tracing". Computer Graphics 24 (4), pp. 377385, 1990

....irradiance, given that the light may reflect off a curved surface and converge or diverge. Two approaches have been used previously to simulate specularly reflected and refracted illumination. If the reflectors and refractors are polyhedral, illumination can be computed by backward beam tracing [Shinya87, Shinya89, Watt90]. For each face of a reflector visible from the light source, the subtended solid angle is traced outward until it reaches a non specular surface, where radiant power is deposited. For curved specular surfaces, backward ray tracing (also called light ray or illumination ray tracing) provides an ....

....along a Fermat path. The combination of the two techniques allows us to calculate directly the illumination via virtual lights at any point in the scene. The intensity law has been used in the two pass rendering algorithms developed by Shinya and Takahashi [Shinya87,Shinya89] and by Watt [Watt90]. What is novel about our approach is that we avoid the second pass, and hence the problem of resampling the light rays by the eye rays. We also formulate the intensity calculation in a way suitable for ray tracing programs. Shinya and Takahashi s formulation requires the notion of paraxial rays, ....

Watt, M. Light-water interaction using backward beam tracing. Computer Graphics, 24, 4 (August 1990) 377-385.

....of the radiance distribution within and leaving a water body is a prerequisite for the solution of many problems in underwater visibility, remote sensing, mixed layer thermodynamics, and realistic image synthesis. Watt describes a backward beam tracing approach to interaction of light with water [25], but his method does not take into account complex optical properties of water bodies. Nishita and Nakamae presented a method that can effectively calculate optical effects [12] Their method focuses primarily on effects such as caustics and shafts of light in water bodies. In this paper we ....

Mark Watt. Light-water interaction using backward beam tracing. In Forest Baskett, editor, Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 377--385, August 1990.

.... a transmission beam is constructed matching the shadow region, and a reflection beam is constructed by mirroring the transmission beam over the polygon s plane (see Figure 3) This method has been used in a variety of applications, including acoustic modeling [16, 24, 44, 51, 59] illumination [13, 22, 25, 27, 30, 60], radio propagation [20] and visibility determination [34, 54] Original Beam Reflection Beam Transmission Beam S S a b c Figure 3: Beam tracing method. The primary advantage of beam tracing is that it takes advantage of spatial coherence, as each beam represents an infinite number of potential ....

Watt, Mark. Light-Water Interaction Using Backward Beam Tracing. Computer Graphics (SIGGRAPH 90), 24, 377-385.

....Deposition using Gaussian Kernels Having determined the area over which we wish to deposit the power, we must now decide how to distribute this power across that area. Rather than distribute the power uniformly across the area which tends to result in aliasing at the edges of the regions (see [Watt90]) we deposit the power as a splat. This technique has been used to implement a progressive refinement algorithm for volume rendering [Laur91] where gaussian splats are used to represent the volume s octtree and the footprint of the splats scaled to match the projected area of the voxels making up ....

....6(b) depicts the relationship between image quality and gaussian spread factor s. The error is at a minimum when s = 0.9. 1.0. To demonstrate the application of the system on complex objects, a classic example of caustic formation, the swimming pool floor, was rendered following the example of [Watt90]. Colour Plate 7 is a view from above, and Colour Plate 8 a view from below the surface of the water. As remarked by Watt, the triangular patch resolution of the water s surface is amplified by the caustic image, requiring very high patch subdivision resolutions. To avoid this we modelled the ....

[Article contains additional citation context not shown here]

Watt M., "Light Water Interaction using Backward Beam Tracing", Computer Graphics, Vol. 24, No. 4, pp. 377-385, August 1990.

....Deposition using Gaussian Kernels Having determined the area over which we wish to deposit the power, we must now decide how to distribute this power across that area. Rather than distribute the power uniformly across the area which tends to result in aliasing at the edges of the regions (see [Watt90]) we deposit the power as a splat. This technique has been used to implement a progressive refinement algorithm for volume rendering [Laur91] where gaussian splats are used to represent the volume s octtree and the footprint of the splats scaled to match the projected area of the voxels making up ....

....used in the example scenes included in this paper has been modelled on Silicate Flint Glass with glass number 635577. 5. Results To demonstrate the application of the system on complex objects, a classic example of caustic formation, the swimming pool floor, was rendered following the example of [Watt90]. Colour Plate 1 is a view from above, and Colour Plate 2 a view from below the surface of the water. As remarked by Watt, the triangular patch resolution of the water s surface is amplified by the caustic image, requiring very high patch subdivision resolutions. To avoid this we modelled the ....

Watt M., "Light Water Interaction using Backward Beam Tracing", Computer Graphics, Vol. 24, No. 4, pp. 377-385, August 1990.

....[DCH88] FLP89] Some of these techniques have been incorporated to other application domains. For example, volume visualization has been applied to CFD data on curvilinear grids [WCA 90] Likewise, concepts from related areas may be fruitfully used in visualization e.g. caustic ray tracing [Wat90] ship wake visualization [Gos90] modeling of rainbows [Mus89] and SONAR range data display [SG89] Since data come in different forms and from different disciplines, a convenient way of handling this inhomogeneity is through a data flow model. Once this abstraction is made, a user interface can ....

M. Watt. Light-water interaction using backward beam tracing. Computer Graphics, 24(4):377--385, August 1990.

....as each beam may be reflected and or obstructed by several surfaces. Another limitation is that reflections off curved surfaces and refractions are difficult to model. Geometric beam tracing has been used in a variety of applications, including acoustic modeling [13, 38, 46, 57] illumination [9, 19, 20, 22, 23, 59], and radio propagation [16] The challenge is to perform geometric operations (i.e. intersection, clipping, and mirroring) on beams efficiently as they are traced recursively through a complex environment. Some systems avoid the geometric complexity of beam tracing by approximating each beam by ....

Watt, Mark. Light-Water Interaction Using Backward Beam Tracing. Computer Graphics (SIGGRAPH 90), 24, 377-385.

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M. Watt, "Light-Water Interaction using Backward Beam Tracing," Computer Graphics, Vol. 24, No. 4, (1990),pp. 377376.

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M. Watt, "Light-water interaction using backward beam tracing ", in Proc. SIGGRAPH 1990, vol. 24, pp. 377--385, (1990).

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Mark Watt. Light-water interaction using backward beam tracing. Computer Graphics, 24(4):327--335, 1990.

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M. Watt. Light-water interaction using backward beam tracing. In Computer Graphics (SIGGRAPH '90 Proceedings) , volume 24, pages 377--385, August 1990.

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Mark Watt. Light-water interaction using backward beam tracing. ACM Computer Graphics, SIGGRAPH'90 Proceedings, pages 377--385, August 1990.

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M. Watt, "Light-Water Interaction using Backward Beam Tracing," Proc. SIGGRAPH'90, 1990, pp.377-385. (a) teapot (b) submarine (c) dolphin(1) (d) dolphin(2) (e) two dolphins(1) (f) two dolphins(2)

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Watt, Mark. "Light-Water Interaction Using Backward Beam Tracing." SIGGRAPH '90, p. 377-385. f38g

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M.Watt, Light-Water Interaction using Backward Beam Tracing," Computer Graphics, Vol.24, No.4 (1990) pp.377-376.

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Watt, M., (1990) "Light-Water Interaction using Backward Beam Tracing," Proceedings of SIGGRAPH '90, in Computer Graphics 24, pp. 377--385. (a) (b)

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Mark Watt. "Light-water interaction using backward beam tracing." In Forest Baskett, editor, Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 377--385, August 1990.

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