4/12/2023 0 Comments 3 d tessellation![]() ![]() In this paper we focus on the resolution part, mainly, as we try to smoothen the tile interfaces to avoid the artifacts like those in Figure 1, for example. That is why traditional mosaicking may correct the light difference phenomenon but the underlying tiles may still be hardly seamless if they vary in resolution. Whilst, the traditional focus of the mosaicking community has been the seamless rendering of tiles that may vary in luminance, little attention has been paid to the heterogeneity due to resolution. In essence, one can safely deduce that even for today's geobrowsers the tessellations are far from being smooth due to varying resolutions or heterogeneous luminance conditions or even both when the tiles have been acquired. Obviously the photographs have been taken at different times and then joined together to what we see in the snapshot. The second snapshot (Figure 1(b)), which pertains to the area surrounding the Pakistani capital of Islamabad, suffers from both heterogeneous resolution and aerial photography in nonidentical light conditions. First is the download latency and second is the nonavailability of proper resolution due to a variety of reasons like area security, data inaccessibility, and the like. Usually there are two reasons for this heterogeneity. In the first example (Figure 1(a)), where the observer is changing his view to the right, it can be seen that the resolution is not uniform. To elaborate this we rely on the two snapshot examples of Google Earth, shown in Figure 1. The problem, however, arises when the tiles have either been rendered at different resolutions or not photographed in identical luminance or radiometric conditions. Traditionally, tile-based approaches have been favored to render large terrains. Additional advantages of the JPEG2000, in this context, include capabilities like better compression and progressive data transfer. ![]() In fact JPEG2000 is better than the popular pyramidal resolution representation with JPEG or other format closer to normal graphic cards that are of high storage cost: there is a need to store different resolutions. It is better to employ some standard state-of-the-art DWT, like the now widely accepted JPEG2000 standard (The ISO/IEC 15444-1 standard.). For LOD, one can rely on the multiresolution nature of the discrete wavelet transform (DWT). This is essential for the terrain tessellation adjustment as a function of the view parameters. One obvious choice is to create multiple levels of detail (LOD) by representing the shape at different levels of approximation. There is a need to reform all these browsers to cater for the diversity of clients through some scalable data structuring. In addition, area coverage by these browsers is slack, if not judicious, in the case of the underdeveloped and developing parts of the world as opposed to their developed counterparts. The contemporary geobrowsers-like Google Earth, NASA's World Wind, or Microsoft's Virtual Earth-give little importance to individual client characteristics, and with the low-end clients, the performance is far from being satisfactory. The methods have been successfully applied to practical examples of both the texture and its corresponding DEM for seamless 3D terrain visualization. Perceptually, this second method has shown better results than the first one. Rather than the traditional sense, the mosaicking employed over here targets the heterogeneous resolution. The window is refined in the DWT domain through mosaicking and smoothing followed by a global inverse DWT. In the second method, though we assume the same tessellation scenario, the view field is thought to be of a sliding window which may contain parts of the tiles from the heterogeneous tessellation. These functions are applied at the DWT subband level and followed by an inverse DWT to give a smoothened tile. The first method is local in that each of the tiles that constitute the view, is subjected to one of the three context-based smoothing functions proposed for horizontal, vertical, and radial smoothing, depending on its localization in the tessellation. We focus on this latter aspect and present two DWT domain methods to seamlessly stitch tiles of heterogeneous resolutions. ![]() Whilst the former has been extensively dealt with in the literature through classic mosaicking techniques, the latter has got little attention. With todays geobrowsers, the tessellations are far from being smooth due to a variety of reasons: the principal being the light difference and resolution heterogeneity.
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