Adaptive Algorithm for Accelerating Direct Isosurface Rendering on GPU

Direct isosurface volume rendering is the most prominent modern method for medical data visualization.It is based on finding intersection points between the rays corresponding to pixels on the screen and isosurface. This article describes a two-pass algorithm for accelerating the method on the graphic processing unit(GPU). On the first pass, the intersections with the isosurface are found only for a small number of rays, which is done by rendering into a lower-resolution texture. On the second pass, the obtained information is used to efficiently calculate the intersection points of all the other. The number of rays to use during the first pass is determined by using an adaptive algorithm, which runs on the central processing unit(CPU) in parallel with the second pass of the rendering. The proposed approach allows to significantly speed up isosurface visualization without quality loss. Experiments show acceleration up to 10 times in comparison with a common ray casting method implemented on GPU. To the authors’ knowledge, this is the fastest approach for ray casting which does not require any preprocessing and could be run on common GPUs.

Emission source-based ozone isopleth and isosurface diagrams and their significance in ozone pollution control strategies

In the past decade,ozone(O_(3))pollution has been continuously worsening in most developing countries.The accurate identification of the nonlinear relationship between O_(3) and its precursors is a prerequisite for formulating effective O_(3) control measures.At present,precursor-based O_(3) isopleth diagrams are widely used to infer O_(3) control strategy at a particular location.However,there is frequently a large gap between the O_(3)-precursor nonlinearity delineated by the O_(3) isopleths and the emission source control measures to reduce O_(3) levels.Consequently,we developed an emission source-based O_(3) isopleth diagram that directly illustrates the O_(3) level changes in response to synergistic control on two types of emission sources using a validated numerical modeling system and the latest regional emission inventory.Isopleths can be further upgraded to isosurfaces when co-control on three types of emission sources is investigated.Using Guangzhou and Foshan as examples,we demonstrate that similar precursor-based O_(3) isopleths can be associated with significantly different emission source co-control strategies.In Guangzhou,controlling solvent use emissions was the most effective approach to reduce peak O_(3) levels.In Foshan,co-control of on-road mobile,solvent use,and fixed combustion sources with a ratio of 3:1:2 or 3:1:3 was best to effectively reduce the peak O_(3) levels below 145 ppbv.This study underscores the importance of using emission source-based O_(3) isopleths and isosurface diagrams to guide a precursor emission control strategy that can effectively reduce the peak O_(3) levels in a particular area.

Spherical Parameterization of Marching Cubes IsoSurfaces Based upon Nearest Neighbor Coordinates

We present some new methods for parameterizing the triangle mesh surface （TMS） which result from the Marching Cubes （MC） algorithm. The methods apply to surfaces of genus zero and the parameter domain is a unit sphere. We take advantage of some special properties of the TMS resulting from the MC algorithm to obtain simple, computational efficient representations of the nearest neighbor coordinates and utilize these coordinates in the characterization of the parameterization by means of systems of equations which are solved iteratively. Examples and comparisons are presented.

Constructing Isosurfaces from 3D Data Sets Taking Account of Depth Sorting of Polyhedra

Creating and rendering intermediate geometric primitives is one of the approaches to visualize data sets in 3D space. Some algorithms have been developed to construct isosurface from uniformly distributed 3D data sets. These algorithms assume that the function value varies linearly along edges of each cell. But to irregular 3D data sets, this assumption is inapplicable. Moreover, the depth sorting of cells is more complicated for irregular data sets, which is indispensable for generating isosurface images or semitransparent isosurface images, if Z-buffer method is not adopted.In this paper, isosurface models based on the assumption that the function value has nonlinear distribution within a tetrahedroll are proposed. The depth sorting algorithm and data structures are developed for the irregular data sets in which cells may be subdivided into tetrahedra. The implementation issues of this algorithm are discussed and experimental results are shown to illustrate potentials of this technique.

Elliptical Splats Based Isosurface Visualization for Volume Data

Elliptical splats are used to represent and render the isosurface of volume data. The method consists of two steps. The first step is to extract points on the isosurface by looking up the case table. In the second step, properties of splats are computed based on local geometry. Rendering is achieved using surface splatting algorithm. The obtained results show that the extraction time of isosurfaces can be reduced by a factor of three. So our approach is more appropriate for interactive visualization of large medical data than the classical marching cubes (MC) technique.

Molecular Recognition of Pyromellitic Imide-azacyclophane to Organic Pollutant

Anion can be identified by pyromellitic imide-azacyclophane which is one of the host compounds.This article investigated the interaction between the host and organic pollution compounds.The host and other eight compounds were optimized by DFT（density functional theory） B3LYP/6-31G level and the energy of compounds was corrected using Boys-Bemardi method.On the basis of B3LYP/6-31G optimized geometries,the RDG function and sign（λ2（r））ρ（r） function values of space points were calculated,and color RDG isosurface map was drawn.3He chemical shift was calculated by the B3LYP/6-31G method.The results showed that the eight organic pollution molecules with the host one shaped stable configurations by hydrogen bonds,respectively.The stabilization energy of complexes 4 and 7 showed repulsion（steric effects） of cyclophane cage observably affecting the stability of the complexes.The location,intensity and the type of interaction in complex 1 were analyzed through color-filled RDG isosurface map.Aromaticity calculations showed that the weak interaction reduced the transverse induction ring current in the host rings,and deteriorated the aromaticity of compounds.

Towards additive manufacturing oriented geometric modeling using implicit functions

Surface-based geometric modeling has many advantages in terms of visualization and traditional subtractive manufacturing using computer-numerical-control cutting-machine tools.However,it is not an ideal solution for additive manufacturing because to digitally print a surface-represented geometric object using a certain additive manufacturing technology,the object has to be converted into a solid representation.However,converting a known surface-based geometric representation into a printable representation is essentially a redesign process,and this is especially the case,when its interior material structure needs to be considered.To specify a 3D geometric object that is ready to be digitally manufactured,its representation has to be in a certain volumetric form.In this research,we show how some of the difficulties experienced in additive manufacturing can be easily solved by using implicitly represented geometric objects.Like surface-based geometric representation is subtractive manufacturing-friendly,implicitly described geometric objects are additive manufacturing-friendly:implicit shapes are 3D printing ready.The implicit geometric representation allows to combine a geometric shape,material colors,an interior material structure,and other required attributes in one single description as a set of implicit functions,and no conversion is needed.In addition,as implicit objects are typically specified procedurally,very little data is used in their specifications,which makes them particularly useful for design and visualization with modern cloud-based mobile devices,which usually do not have very big storage spaces.Finally,implicit modeling is a design procedure that is parallel computing-friendly,as the design of a complex geometric object can be divided into a set of simple shape-designing tasks,owing to the availability of shape-preserving implicit blending operations.

Structural analysis of processed corneas

Background:Disruption of the microstructure in corneal stroma can lead to the loss of transparency.The lack of a characterization method for the microstructure prevents such scaffolds to be implemented in tissue transplantation.The non-invasive,three-dimensional(3D)rendering multiphoton microscopy(MPM)poses the potential to solve this problem.Methods:MPM images and data analyses were performed with three kinds of samples with known and different quality.Isosurfaces(ISOs)were constructed for the evaluation of void volume and collagen distribution.Results:The differences in the microstructures of these samples were revealed with clear indications and links to their behaviours in rehydration and possible transparency.According to this analysis,the scaffold with the highest void space ratio amongst the three presented the highest successful rates to be thoroughly rehydrated.Conclusions:Such a method can be developed for assessing the quality of tissue engineered corneas,or donated corneas,and be useful as a powerful research tool in cornea related research.

2D-Manifold Boundary Surfaces Extraction from Heterogeneous Object on GPU

The conventional isosurface techniques are not competent for nleshing a heterogeneous object because they assume that the object is homogeneous. Thus the visualization method taking the heterogeneity into account is desired. In this paper, we propose a novel algorithm to extract the boundary surfaces from a heterogeneous object in one pass, whose remarkable advantage is free of the number of materials contained. The heterogeneous object is first classified into a series of homogeneous material components. Then each component is enclosed with a 2D-manifold boundary surface extracted via our algorithm. The information important to the heterogeneous object is also provided, such as the interface between two materials, the intersection curve where three materials meet and the intersection point where four materials meet. To improve the performance, the algorithm is also designed and implemented on GPU. Experimental results demonstrate the effectiveness and efficiency of the proposed algorithm.

Efficient ray casting of volumetric images using distance maps for empty space skipping

Volume and isosurface rendering are methods of projecting volumetric images to two dimensions for visualisation.These methods are common in medical imaging and scientific visualisation.Head-mounted optical see-through displays have recently become an affordable technology and are a promising platform for volumetric image visualisation.Images displayed on a head-mounted display must be presented at a high frame rate and with low latency to compensate for head motion.High latency can be jarring and may cause cybersickness which has similar symptoms to motion sickness.Volumetric images can be very computationally expensive to render as they often have hundreds of millions of scalar values.Fortunately,certain materials in images such as air surrounding an object boundary are often made transparent and need not be sampled,which improves rendering efficiency.In our previous work we introduced a novel ray traversal technique for rendering large sparse volumetric images at high frame rates.The method relied on the computation of an occupancy and distance map to speed up ray traversal through empty regions.In this work we achieve higher frame rates than our previous work with an improved method of resuming empty space skipping and the use of anisotropic Chebyshev distance maps.An optimised algorithm for computing Chebyshev distance maps on a graphical processing unit is introduced supporting real-time transfer function editing.