AutoCAD® 2002 - Autodesk

major axis length, b is the negative of 1/2 the minor axis length, and c is the
center point (2-D) of the ellipse.
Because this is actually a vector equation and the variable c is actually a point
with X and Y values, it really should be written as:
p(u)=(Cx+a*cos(u))*i+(Cy+b*sin(u))*j
where
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Cx is the X value of the point c
Cy is the Y value of the point c
a is –(1/2 of the major axis length)
b is –(1/2 of the minor axis length)
i and j represent unit vectors in the X and Y directions
HATCH
In AutoCAD, once the axis endpoints are selected, all you have left to specify
is the start and end of the elliptical arc.
When you select the parameter option, you are asked for a start parameter
and an end parameter. These values are plugged into the equation to determine
the actual start and end points on the ellipse. The rest of the ellipse is
filled in between these two points in a counterclockwise direction from the
first parameter to the second. The value entered for the parameter u is taken
to be degrees for the purposes of obtaining the cos(u) and sin(u).
For example:
Axis endpoint 1 = 0,1
Axis endpoint 2 = 4,1
Other axis distance = 2,0
Start parameter = 270
End parameter = 0
generates the start point at 2,2 and the end point at 0,1 and fills in the ellipse
from 2,2 to 0,1 in a counterclockwise direction.
The following group codes apply to hatch entities. In addition to the group
codes described here, see “Common Group Codes for Entities” on page 60.
78 | Chapter 6 ENTITIES Section