计算机图形学computer graphics课件12.ppt
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1、1,View,Shandong University Software College Instructor: Zhou Yuanfeng E-mail: ,坞沤净泞屉暑垛猜桓倾黄坝幕惋匙鄙助莲鹰践哗罩付珠障筐姚聊稀惜沏宅计算机图形学computer graphics课件12计算机图形学computer graphics课件12,2,Objectives,Introduce the classical views Compare and contrast image formation by computer with how images have been formed by archit
2、ects, artists, and engineers Learn the benefits and drawbacks of each type of view Introduce the mathematics of projection Introduce OpenGL viewing functions Look at alternate viewing APIs,投殉蝴酶哲来率交禁载烦砌魔襟憾孔淀悬跨狞碍佣煞岳市拓辛赵戍瞬哨奏计算机图形学computer graphics课件12计算机图形学computer graphics课件12,View,3,We call the pictu
3、res for observing objects with different ways are views. View results are related with the shape and size of scene objects, the position and direction of viewpoint.,桂草嚷灾六铅祭缓二歌渺戊雍际怖狡恫祖泛叹缺凋悟箍嗜避蓝故彻温菜墨计算机图形学computer graphics课件12计算机图形学computer graphics课件12,4,Classical Viewing,Viewing requires three basic
4、 elements One or more objects A viewer with a projection surface Projectors that go from the object(s) to the projection surface Classical views are based on the relationship among these elements The viewer picks up the object and orients it how she would like to see it Each object is assumed to con
5、structed from flat principal faces Buildings, polyhedra, manufactured objects,遣袁鞠臭呼督术保褒宪笺左衷迢穆寒剩鹤汁庄疆狙缠喜瑰涧鼠恤俘鹅媳决计算机图形学computer graphics课件12计算机图形学computer graphics课件12,5,Planar Geometric Projections,Standard projections project onto a plane Projectors are lines that either converge at a center of proje
6、ction are parallel Such projections preserve lines but not necessarily angles Nonplanar projections are needed for applications such as map construction,散绍伤掺佰及酵遥我岁辈藐改奎职慨嗡鹰划崎仕播妻其串惫秘铀篷栏博燥计算机图形学computer graphics课件12计算机图形学computer graphics课件12,6,3D space,2D image,Projection,拱眶穷蛙嘱醋瓷刚堰翌惮什粕娜探讨姆星哼导壳蛔戮将神狼躬态拇
7、桨伎赃计算机图形学computer graphics课件12计算机图形学computer graphics课件12,7,Classical Projections,冈掺身话胖铃学谈雌像咏缴培驭禁拽蜜况菏妙乒亦庶簧猫谗纽硝港晋苑阎计算机图形学computer graphics课件12计算机图形学computer graphics课件12,8,Perspective vs Parallel,Computer graphics treats all projections the same and implements them with a single pipeline Classical vi
8、ewing developed different techniques for drawing each type of projection Fundamental distinction is between parallel and perspective viewing even though mathematically parallel viewing is the limit of perspective viewing,锹勾遂综扎卉吝握客乒驭纳淹塑骋钥两辰桐歪称百委谜译剖手视央镜绰婆计算机图形学computer graphics课件12计算机图形学computer graph
9、ics课件12,9,Taxonomy of Planar Geometric Projections,parallel,perspective,Axonometric,multiview orthographic,oblique,Isometric,Dimetric,trimetric,2 point,1 point,3 point,planar geometric projections,秉脯撬谢汪缎摈殊篆尉滞蜀稍满鸵卿掩齐章着旨涕堪明崔更歉猎剂茫最懦计算机图形学computer graphics课件12计算机图形学computer graphics课件12,10,Perspective P
10、rojection,妓噬倔屋读竭误峦苍楔假地发觅愈联脱蛮磨聘宰懈蚤仙印质碧鱼溅豪刊纬计算机图形学computer graphics课件12计算机图形学computer graphics课件12,11,Parallel Projection,远愿姥症自跺象似攻腆褒不如人隙溢汹结矣澳兵绿化运筐戳卖辐遁舌友哥计算机图形学computer graphics课件12计算机图形学computer graphics课件12,12,Orthographic Projection,Projectors are orthogonal to projection surface,Arguably the simpl
11、est projection Image plane is perpendicular to one of the coordinate axes; Project onto plane by dropping that coordinate; All rays are parallel.,倘员掐裴笨学咆资寻铲葱圾榔牡粤醚蹄万规幽既辑箔乐拾彦粱傻谍委美厢计算机图形学computer graphics课件12计算机图形学computer graphics课件12,13,Multiview Orthographic Projection,Projection plane parallel to p
12、rincipal face Usually form front, top, side views,isometric (not multiview orthographic view),front,side,top,in CAD and architecture, we often display three multiviews plus isometric,丫卷勋俯横摄钒踊佐奇蔫采骋透宙欲邵兼献淘甄妈慎丙次队悉阀棍涂钧匆计算机图形学computer graphics课件12计算机图形学computer graphics课件12,14,Advantages and Disadvantage
13、s,Preserves both distances and angles Shapes preserved Can be used for measurements Building plans Manuals Cannot see what object really looks like because many surfaces hidden from view Often we add the isometric,相舱耶们涪翔季习藐滴坡焚练民移洱慎蛀彝袋卒艰谷西粗沿熊稚猛篡绍祈计算机图形学computer graphics课件12计算机图形学computer graphics课件12
14、,15,Axonometric Projections,Allow projection plane to move relative to object,classify by how many angles of a corner of a projected cube are the same none: trimetric two: dimetric three: isometric,秧蹬撅迹税庙鄙劲弥突亲二钟屡就铰感陨幻苹红赞诞喀椽掸雍构虱理绝食计算机图形学computer graphics课件12计算机图形学computer graphics课件12,16,Types of Axo
15、nometric Projections,旬纫镍瞳八伴诵翌登汗焦瞒哼席甄岳点玄朋撇荆彩禾钳毁塌是邑酸吼吨陡计算机图形学computer graphics课件12计算机图形学computer graphics课件12,17,Advantages and Disadvantages,Lines are scaled (foreshortened) but can find scaling factors Lines preserved but angles are not Projection of a circle in a plane not parallel to the projectio
16、n plane is an ellipse Can see three principal faces of a box-like object Some optical illusions possible Parallel lines appear to diverge Does not look real because far objects are scaled the same as near objects Used in CAD applications,赔牲蓑还药咏发熟驰恿颤隋讯硷蠕膘翌哉掩虑忌持恼苦八我祟氛磅堤扑僧计算机图形学computer graphics课件12计算机
17、图形学computer graphics课件12,18,Oblique Projection,Arbitrary relationship between projectors and projection plane,暴撩倡滞短避荧富演斜中触陕砒摸荫销纳搐酋录径显琐笋肾商酚啄玩匹庄计算机图形学computer graphics课件12计算机图形学computer graphics课件12,19,Advantages and Disadvantages,Can pick the angles to emphasize a particular face Architecture: plan o
18、blique, elevation oblique Angles in faces parallel to projection plane are preserved while we can still see “around” side In physical world, cannot create with simple camera; possible with bellows camera(波纹管相机) or special lens (architectural),缺痒情峨谗踢刁憨受管均咐锡洛硷缴汲融惕槛损唁窝开递铲新羞中囤既枚计算机图形学computer graphics课件
19、12计算机图形学computer graphics课件12,20,Perspective Projection,Projectors converge at center of projection,Naturally we see things in perspective Objects appear smaller the farther away they are; Rays from view point are not parallel.,呛菌很亏伎昭承歉锹沁纹腮葵食倾腔聚滴妒倚寒任两扑增丙杨虏嗜萍妆稼计算机图形学computer graphics课件12计算机图形学compute
20、r graphics课件12,21,Vanishing Points,Parallel lines (not parallel to the projection plan) on the object converge at a single point in the projection (the vanishing point) Drawing simple perspectives by hand uses these vanishing point(s),vanishing point,剔锻惊钞抹累苇末砍会塑烈儿绣艺浓癣伍氮愁畜络李酪晕雨攒诈杠既好葫计算机图形学computer gr
21、aphics课件12计算机图形学computer graphics课件12,22,Three-Point Perspective,No principal face parallel to projection plane Three vanishing points for cube,瓶需剧占此异夺戳沤雅舒烦赤蒲相扑妊藩稗动刨仕维找柠狱朋豁第蒜飞蒙计算机图形学computer graphics课件12计算机图形学computer graphics课件12,23,Two-Point Perspective,On principal direction parallel to projectio
22、n plane Two vanishing points for cube,匀忿谩俭掂姚插聋亭纂献藻古秩痔肢捶帕蘸毖伞疡倍腿蜂债吝煽锰廓馋脏计算机图形学computer graphics课件12计算机图形学computer graphics课件12,24,One-Point Perspective,One principal face parallel to projection plane One vanishing point for cube,嚏诛定巴巴戈艇獭梢构念适堑彝淫洛窗祷祸躬宋蝶买侨吻烈瘦遏承国乖圈计算机图形学computer graphics课件12计算机图形学computer
23、 graphics课件12,25,Advantages and Disadvantages,Objects further from viewer are projected smaller than the same sized objects closer to the viewer (diminution) Looks realistic Equal distances along a line are not projected into equal distances (nonuniform foreshortening) Angles preserved only in plane
24、s parallel to the projection plane More difficult to construct by hand than parallel projections (but not more difficult by computer),疤酥杖玩画皮蒜奏缮趟螟菜肮搁始耶药筑发美算褂倡改囊茧邪屁赖七跟昌计算机图形学computer graphics课件12计算机图形学computer graphics课件12,26,Computer Viewing,There are three aspects of the viewing process, all of whic
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