1. 正投影圖 3D object is projected onto a plane orthogonally
Parallel projectors
Perpendicular
Projection plane

2. 正投影圖 (2) Six basic views:
You can project the object in six orthographic directions
The resulting views are called basic views
You may imagine the object is placed inside a transparent box
Transparent box
Six basic views

3. 正投影圖 (3)
Because it is inconvenient to carry the box around, the box is unfolded onto a common plane – drawing paper
External faces of the box

4. Object imagined to be cut w/ frontal part removed
切面圖
Object is imagined to be cut by a plane & the portion nearer to observer is removed.
Interior is exposed & shown in continuous lines
Hatching is applied at plane of cutting
Object imagined to be cut w/ frontal part removed

5. 切面圖 (2)
A thin chain line w/ thick continuous lines at both ends to illustrate the imaginary cutting plane
A labeled sectional view w/ portion of object removed
Cutting line is drawn on a view adjacent to sectional view
Cutting line w/ label & direction of viewing after cut
Since sectional cutting is imaginary, all other views remain uncut
Normal top & side views, a sectional front view
SECTION A_A

6. 軸測投影圖 Constructing an axonometric projection 90o C A G C’ A’ F O E B’
Draw a circle of any convenient size. Locate OA & OB by the angle of rotation & angle of tilt respectively
From B project vertically to cut the horizontal axes at E
From E draw an arc to cut OA & OC at F & G
Draw horizontal line from B to meet the vertical axis at B’
Draw horizontal lines from F & G to meet the vertical projections of A & C at A’ & C’.
OA’ OB’ & OC’ will be the locations of the three axes of the object in axonometric projection.
If OA OB & OC are the natural lengths of the object, OA’ OB’ & OC’ will be their lengths as appeared on the drawing.
The length along the axes are foreshortened in the following ratio:-
axis OA OA’/OA
axis OB OB’/OB
axis OC OC’/OC
90o
Angle of rotation A B C O F G B’ A’ C’ E
Angle of tilt

7. 透視投影圖 Constructing a perspective projection
This is a type of pictorial drawing.
It differs from axonometric projection & oblique projection in that the view is projected onto the picture plane by non-parallel projection lines merging to a single point called the station point (SP)
SP can be regarded as the position of the viewer’s eye
One-point perspective – 2 axes or 1 face is parallel to the picture plane (PP)
Two-point perspective – 1 axis of the object is parallel to the picture plane
Three-point perspective – none of the axes is parallel to the picture plane PP SP VP EL VP PP SP VP