2) Let us recognize the plane coordinate and the start and end angles of a
circular arc.
In Plane XY
XZ or YZ, the coordinate of a point is its position with
respect to the zero point on the plane.
The coordinate of zero point O:(0,0)
The coordinate of Point A:(20,20)
The coordinate of Point B:(30,10)
The coordinate of Point C:(-20,20)
The coordinate of Point D:(-30,10)
The coordinate of Point E:(-30,-10)
The coordinate of Point F:(-20,-20)
The coordinate of Point G:(30,-10)
The coordinate of Point H:(20,-20)
In Plane XY
XZ or YZ, the start and end angle of a circular arc is
counted in anti clockwise.
As shown in Fig. 3:
From A to B 0
90
Arc AB
Form B to A 90
0
From B to C 90
180
Arc BC
From C to B 180
90
From C to D 180
270
Arc CD
From D to C 270
180
From A to D 360
270
Arc DA
From D to A 270
360
From E to B 45
90
Arc BE
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