Disparity curvature and the perception of three-dimensional surfaces

BINOCULAR stereopsis provides information about the relative distance of objects from the differences in the horizontal position of their images on the two retinas. Because the size of the disparity between two points is inversely related to the square of the viewing distance, it is usually assumed that disparities have to be scaled according to distance using the vergence angle of the eyes, or by using the small vertical disparities that also exist between corresponding points of the two images. Here we present evidence that the visual system could extract information about the shapes of surfaces (without the need for scaling) by using the second spatial derivative of disparity--disparity curvature--which remains invariant with viewing distance. Rather than computing the second derivative, we suggest that an approximation to disparity curvature could be derived from the differences in curvature of corresponding line elements in the two eyes.     

Vertical disparity pooling and the induced effect

If the image received by one eye is vertically magnified by a small amount then an illusory tilt is perceived around the vertical axis through the fixation point. This is known as the induced effect and it can be explained by a recent computational theory of binocular vision which treats it as a side-effect of the use of vertical disparities to recover information about the distance to the fixation point and the angle of gaze. We have investigated the consequences of introducing vertical magnifications of some parts of a scene and not others and report here that there is a simple linear relationship between the size of the induced effect and the average vertical magnification. This suggests that a pooling strategy is adopted in the measurement of vertical disparities, a result which fits in well with expectations of the theory.     

Monocular aniseikonia: a motion parallax analogue of the disparity-induced effect

Mayhew and Longuet-Higgins have recently outlined a computational model of binocular depth perception in which the small vertical disparities between the two eyes' views of a three-dimensional scene are used to determine the 'viewing parameters' of fixation distance (d) and the angle of asymmetric convergence of the eyes (g). The d/g hypothesis, as it has been called, correctly predicts that a fronto-parallel surface, viewed with a vertically magnifying lens over one eye, should appear to be rotated in depth about a vertical axis. We report here a comparable illusion for surfaces specified by monocular motion parallax information, which can be explained more simply by considering the differential invariants of the optic flow field. In addition, our observations suggest that the disparity-induced effect is not a 'whole field' phenomenon nor one limited to small magnification differences between the eyes.     

Perception of three-dimensional shape influences colour perception through mutual illumination

Objects in the natural world possess different visual attributes, including shape, colour, surface texture and motion. Previous perceptual studies have assumed that the brain analyses the colour of a surface independently of its three-dimensional shape and viewing geometry, although there are neural connections between colour and two-dimensional form processing early in the visual pathway. Here we show that colour perception is strongly influenced by three-dimensional shape perception in a novel, chromatic version of the Mach Card--a concave folded card with one side made of magenta paper and the other of white paper. The light reflected from the magenta paper casts a pinkish glow on the white side. The perceived colour of the white side changes from pale pink to deep magenta when the perceived shape of the card flips from concave to convex. The effect demonstrates that the human visual system incorporates knowledge of mutual illumination-the physics of light reflection between surfaces--at an early stage in colour perception.     

Depth is encoded in the visual cortex by a specialized receptive field structure

Binocular neurons in the visual cortex are thought to perform the first stage of processing for the fine stereoscopic depth discrimination exhibited by animals with frontally located eyes. Because lateral separation of the eyes gives a slightly different view to each eye, there are small variations in position (disparities), mainly along the horizontal dimension, between corresponding features in the two retinal images. The visual system uses these disparities to gauge depth. We studied neurons in the cat's visual cortex to determine whether the visual system uses the anisotropy in the range of horizontal and vertical disparities. We report here that there is a corresponding anisotropy in the cortical representation of binocular information: receptive-field profiles for left and right eyes are matched for cells that are tuned to horizontal orientations of image contours. For neurons tuned to vertical orientations, left and right receptive fields are predominantly dissimilar. Therefore, a major modification is required of the conventional notion of disparity processing. The modified scheme allows a unified encoding of monocular form and binocular disparity information.     

Three-dimensional illusory contours and surfaces.

Under general viewing conditions, objects are often partially camouflaged, obscured or occluded, thereby limiting information about their three-dimensional position, orientation and shape to incomplete and variable image cues. When presented with such partial cues, observers report perceiving 'illusory' contours and surfaces (forms) in regions having no physical image contrast. Here we report that three-dimensional illusory forms share three fundamental properties with 'real' forms: (1) the same forms are perceived using either stereo or motion parallax cues (cue invariance); (2) they retain their shape over changes in position and orientation relative to an observer (view stability); and (3) they can take the shape of general contours and surfaces in three dimensions (morphic generality). We hypothesize that illusory contours and surfaces are manifestations of a previously unnoticed visual process which constructs a representation of three-dimensional position, orientation and shape of objects from available image cues.     

基于投影特征的商标图像检索方法

针对二值商标图像,提出了一种基于极坐标系投影特征的检索方法.利用商标图像在极坐标系的水平投影特征及垂直投影特征来描述商标图像的形状特征,利用投影特征向量的欧拉距离来度量图像的相似性程度.实验结果证明采用此方法具有良好的平移、旋转及尺度不变性,具有很好的检索精度.     

An unexpected specialization for horizontal disparity in primate primary visual cortex

The horizontal separation of the eyes means that objects nearer or farther than the fixation point project to different locations on the two retinae, differing principally in their horizontal coordinates (horizontal binocular disparity). Disparity-selective neurons have generally been studied with disparities applied in only one direction (often horizontal), which cannot determine whether the encoding is specialized for processing disparities along the horizontal axis. It is therefore unclear if disparity selectivity represents a specialization for naturally occurring disparities. I used random dot stereograms to study disparity-selective neurons from the primary visual cortex (V1) of awake fixating monkeys. Many combinations of vertical and horizontal disparity were used, characterizing the surface of responses as a function of two-dimensional disparity. Here I report that the response surface usually showed elongation along the horizontal disparity axis, despite the isotropic stimulus. Thus these neurons modulated their firing rate over a wider range of horizontal disparity than vertical disparity. This demonstrates that disparity-selective cells are specialized for processing horizontal disparity, and that existing models of disparity selectivity require substantial revision.     

面向web三维应用的气象雷达矢量剖面生成

气象雷达矢量剖面主要负责监测与研究强对流天气的面向web三维应用的三维结构特征,传统剖面生成无法能够保证空间连续性,不能最大程度保留特征。为此,提出一种新的面向web三维应用的气象雷达矢量剖面生成方法。确定雷达反射率因子垂直剖面基线。在此基础上,由剖线左端某点着手,分别求出剖线上各点的垂直距离与方位角。设定剖面上同剖线点相对应的空间垂直线点,计算其反射率强度,通过径向、方位上的最近邻与垂直线性内插结合的插值方法生成气象雷达矢量剖面图。依据相同高度的雷达数据,研究气象雷达回波信息在一定高度上的水平分布,将其和该高度相邻天气图结合在一起,获取面向三维应用的不同天气的三维结构。实验结果表明,所提方法生成的气象雷达矢量剖面空间位置合理,在水平与竖直方向均有很好的空间连续性,分辨率高,分析值和观测值更加接近。将所提方法应用于气象预测中,能够有效完成预测,应用性强。     

BIM云平台中三维模型的任意剖切

针对BIM云平台中三维模型的剖切通过移动竖向或横向的剖切面来实现,剖切方式不灵活,仅是选择性渲染的效果且无法自动获得剖切面的信息的问题。基于Unity3D提出了一种对复杂BIM模型进行任意角度剖分并缝合原模型及剖面的分割算法。运用该分割算法可以从任意角度对BIM云平台中三维模型进行剖切并得到所有剖切点,根据分组排序的剖切点自动计算出每个被剖切构件剖切面的面积、圆形管件的直径以及管件之间的距离。该剖切方法在实现任意剖切的基础上获取到剖切面的关键信息,能够更好的指导现场施工作业。     

超大屏幕自由立体显示系统关键技术的研究

为了获得低成本超大屏幕自由立体显示器,采用了DLP投影的技术方案.分析了柱透镜光传输特性.通过模拟透镜光路,获得了立体视区图.结合立体视区的交叉干扰现象,推导出适合大屏幕立体显示的光栅参数.针对显示器的最佳观看距离,分析了虚拟摄像机架设间距和前后景极限位置的关系.实现了约150 in超大屏幕立体显示墙,同时提高了显示系统的立体感和临场感.     

基于VRML的采空区信息管理系统的开发

 针对矿山企业因采空区数量逐渐增多而难以对其进行有效管理的现实问题,提出了一种基于网络的采空区信息管理系统设计与开发方法。以采空区信息获取为基础,运用采空区精密探测系统(CMS)、矿业软件Surpac、数字化软件QVOL和三维模型编辑器Vrmlpad准确获取采空区的二维和三维信息,开发基于B/S模式的采空区信息管理系统。系统实现了用户管理,采空区二维信息增加、删除、修改、查询和打印,通过IE等浏览器查看采空区三维模型,三维形态信息网络传输与管理,可以满足现阶段矿山企业各部门远程对采空区信息进行管理的要求,为矿山采空区安全监管提供了一种新的技术手段。     

Colour-contingent after-effects are really wavelength-contingent

McCollough reported that following adaptation to (say) a red and black pattern of vertical stripes, alternating every few seconds with a green and black pattern of horizontal stripes, an orientation-contingent colour after-effect is observed when black and white gratings are viewed. Vertical gratings are tinged with green and horizontal gratings with pink. We have exploited colour constancy, the tendency for objects to appear constant in hue despite large changes in the spectral composition of the illuminant, to examine whether the colours observed on the McCollough effect test gratings are determined by the wavelength composition of the adaptation patterns or by their perceived colour. The key to this approach can be illustrated by Edwin Land's elegant demonstrations of colour constancy using 'Mondrian' displays. By embedding the adapting grating that is used to induce the McCollough effect within a Mondrian we show that the effect depends upon the wavelength of light coming from the grating, rather than the perceived colour.     

Realization of Super Large Autostereoscopic Display Wall

The suitable lenticular lens for large panel autostereoscopic display was designed,and its optical transmission property was analyzed.The location of the best viewing zones and the relationship between screen size and the optimum viewing distance were proposed.On the basis of the original monitor,rear projection screen material suitable for large panel three-dimensional(3D) monitor and splicing method for 3D display wall were studied.Close to 150-inch-large panel stereo display wall was achieved.     

Sensitivity for vertical retinal image differences

The detection of horizontal disparities between the right and left retinal images is accepted as an important component in the visual perception of depth. It has occasionally been pointed out that a disparity will also occur in the vertical when a target is nearer to one eye than the other and could be used as a second component. Here it is shown that while it is possible to detect size differences between the retinal images in the vertical direction, the sensitivity is at least one order of magnitude less than the horizontal differences. It had been generally accepted that vertical disparities cannot be detected (literature summarized by Tschermak), but there are clear reports of the ability of subjects to respond to relative differences in the vertical magnification of the images of the two eyes, the so-called induced size effect. It manifests itself in the appearance of a visual scene as if there had been an opposite horizontal magnification and is, therefore, in the correct direction if it is to be utilized in asymmetrical convergence.     

考虑不均匀沉降的大跨网架结构地震反应分析

针对不均匀沉降对大跨网架结构地震反应的不利影响,提出在柱顶设置不同隔震支座以减小不均匀沉降下结构的地震反应.建立大跨网架结构数值模型,进行模态分析,对比其动力特性.耦合不均匀沉降与地震作用,数值分析得到未发生不均匀沉降和发生不均匀沉降的三种结构在水平地震和竖向地震作用下的动力反应.结果表明,不均匀沉降导致结构发生内力重分布,使不同类型的杆件有大小不同的附加应力;不均匀沉降增大了网架结构的地震反应,也降低了隔震效果;三维隔震支座的竖向刚度较小,能够适应不均匀沉降带来的竖向变形,且对竖向地震作用的隔震效果显著,在发生不均匀沉降时仍具有一定隔震效果,而水平隔震支座则没有.     

建筑物尺度对避雷针防雷性能影响的数值评估

为研究闪电先导与地面建筑物的相互作用,根据长间隙放电的物理过程建立了包含上行迎面正先导的三维负极性先导发展模型。利用模拟电荷法计算了电晕区的电位分布及电晕电荷量,作为上行正先导是否满足激发起始的判断条件,建立了上行正先导的起始传播模型,利用该模型评估了建筑物形状特征对于闪击距离的影响。研究表明:随着回击电流峰值、建筑物垂直高度或避雷针高度的增大,闪击距离也逐步增大;在建筑物垂直高度不变的条件下,随着避雷针高度的增加,闪击距离逐步增大,当避雷针高度大于30m后,闪击距离的变化不再明显。     

方管铝型材喷水冷却温度场模拟及影响因素分析

为了解决方管铝型材冷却不均的问题,利用有限元分析软件Fluent,对方管铝型材喷水冷却的温度场进行了三维瞬态数值模拟,分析了方管铝型材特征点的温度场变化规律,研究了挤出成形速度、喷嘴纵向间距及喷嘴横向间距对方管铝型材冷却温度场的影响.结果表明:挤出成形速度和喷嘴纵向间距对方管铝型材纵向温度场影响明显,而喷嘴横向间距对温度场的影响主要表现在横向上.采用最大的挤出成形速度、最小的喷嘴纵向间距和80mm的喷嘴横向间距可以得到较均匀的冷却温度场.     

基于空间结构的杉木枝下高可视化模拟研究

【目的】定量研究林分空间结构对杉木枝下高的影响,构建基于空间结构的枝下高模型,结合杉木生长模型,应用三维可视化技术,实现杉木枝下高可视化模拟。【方法】利用湖南省黄丰桥国有林场6块杉木人工林临时样地的调查数据,选择5个常用枝下高基础模型,分析水平空间结构参数(P_H)、垂直空间结构参数(P_V)和空间结构单元平均距离(d_DIS)及其组合对枝下高的影响,构建综合指标较好且变量少的枝下高模型。基于林分三维模型实时生成方法,建立一种枝干可控的杉木三维模型;结合单木胸径连年生长量模型、树高-曲线模型和冠幅面积估计模型,模拟林木的生长状态。【结果】Logistic模型综合指标较好且模型参数可解释,可选为基础模型;3个空间结构参数中垂直空间结构影响较为显著,将P_V加入到Logistic模型中,改善了枝下高模型的拟合效果,决定系数(R²)从0.717提升到0.741,估计值的标准差从1.407 m减小到1.321 m,并使各项模型检验误差指标有所减小;构建的杉木三维模型可以动态调节枝干,实现了杉木枝下高模拟。【结论】构建的枝下高模型可以应用于林木年龄和部分林分信息未知的杉木林中,体现了林木间的相互竞争影响;结合枝干可控的杉木三维模型,模拟杉木生长过程,形象直观地表现了杉木枝下高的变化,为进一步研究林分生长动态可视化模拟和森林经营可视化模拟提供支持。     

Content-based similarity for 3D model retrieval and classification

With the rapid development of 3D digital shape information, content-based 3D model retrieval and classification has become an important research area. This paper presents a novel 3D model retrieval and classification algorithm. For feature representation, a method combining a distance histogram and moment invariants is proposed to improve the retrieval performance. The major advantage of using a distance histogram is its invariance to the transforms of scaling, translation and rotation. Based on the premise that two similar objects should have high mutual information, the querying of 3D data should convey a great deal of information on the shape of the two objects, and so we propose a mutual information distance measurement to perform the similarity comparison of 3D objects. The proposed algorithm is tested with a 3D model retrieval and classification prototype, and the experimental evaluation demonstrates satisfactory retrieval results and classification accuracy.