Chapter 6 -- ENTITIES Section ELLIPSE

The following group codes apply to ellipse entities. In addition to the group codes described here, see "Common Group Codes for Entities." For information about abbreviations and formatting used in this table, see "Formatting Conventions in This Reference."

Ellipse group codes
 Group codes Description 100 Subclass marker (AcDbEllipse) 10 Center point (in WCS)DXF: X value; APP: 3D point 20, 30 DXF: Y and Z values of center point (in WCS) 11 Endpoint of major axis, relative to the center (in WCS)DXF: X value; APP: 3D point 21, 31 DXF: Y and Z values of endpoint of major axis, relative to the center (in WCS) 210 Extrusion direction (optional; default = 0, 0, 1)DXF: X value; APP: 3D vector 220, 230 DXF: Y and Z values of extrusion direction  (optional) 40 Ratio of minor axis to major axis 41 Start parameter (this value is 0.0 for a full ellipse) 42 End parameter (this value is 2pi for a full ellipse)

The group codes 41 and 42 are the start and end values for u in the equation below. The magnitude of the codes 11,21,31 vector is equal to 1/2 of the major axis which is the a value in the equation. The point 10,20,30 is the c value in the equation. Knowing all these, we can calculate the b value to complete the equation.

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