(3.1.1)--2.1.1投影法、正投影的基本性质、视图的基本概念.ppt

《(3.1.1)--2.1.1投影法、正投影的基本性质、视图的基本概念.ppt》由会员分享，可在线阅读，更多相关《(3.1.1)--2.1.1投影法、正投影的基本性质、视图的基本概念.ppt（11页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、2.Projection basis 2.1 Basic concepts of projection method and view2.1.1 Projection methodHow did the shadow form?Objects in sunlight or light,will produce shadows on the wall or on the ground.This phenomenon is called projection.Three conditions for projection formation(1)Objects:different objects

2、have different shadows.(2)Light source:if there is more than one light source,the same object at the same position has different shadows.(3)Projection surface:The same object at the same position has different shadows when the shadow falls to different places.Projection surfaceProjection surfaceGrey

3、 and black shadowsObjects ObjectsLight sourceLight sourceLightProjection of the three elements,the absence of one can notClassification of projection method:Center projection methodParallel projection methodprojection methodDrawing perspective viewsDrawing oblique axonometric drawingsDrawing orthogr

4、aphic axonometric drawingsOblique projectionOrthographic projectionSingle-sided projectionMulti-sided projectionDrawing engineering drawingsCenter projection method:Projection CenterProjection HughProjection rayProjectionProjection surfaceProjection surfaceThe projection size changes when the object

5、s position changes.Projection characteristicsThe projection obtained by the center projection method does not reflect the true size of the object.It is less measurable and more complicated to draw.Parallel projection method:Orthographic projection method:The projection lines are parallel to each oth

6、er and perpendicular to the projection surface(it can accurately and completely express the shape of the body and structure,simple for drawing,good in measurement,so it is widely used in engineering drawings)Oblique projection method:The projection lines are parallel to each other and inclined to th

7、e projection surface(poor stereoscopic impression)Projection line is perpendicular to the projection planeProjection restOrthographic projectionThe projection ray is inclined to the projection planeProjection surfaceProjection surfaceProjection restOblique projectionOrthographic Projection Applicati

8、on -Orthographic Axonometric DrawingOblique Projection Application-Oblique axonometric drawingMulti-sided Orthographic Projection-Application a Combination1.Authenticity:If a straight line segment or plane figure parallel to the projection surface,its projection can reflect the real length or implem

9、entation.2.Accumulation:If a straight line segment or plane figure perpendicular to the projection surface,its projection accumulates is a point or a straight line.The projection of a point,line,figure,etc.on a straight line or surface falls on the accumulation projection of a straight line or plane

10、 respectively.3.Similarity:If a straight line segment or plane figure inclined to the projection surface,its projection is shorter than the real length or smaller than the real shapes(but similar to the spatial figure).2.1.1 Basic properties of orthographic projectionThe projection of an object drawn by the orthographic projection method is called a view.2.1.1 Basic concepts of viewProjection surfaceProjection surfaceObjectThe line of sight is parallel and perpendicular to the projectionThe human line of sight is the projection line