Ellipse Construction, ContinuedFoci methodThe foci method of ellipse construction involves plotting a series of pointsalong the circumference of the ellipse by drawing a series of intersecting arcsusing the foci on the major axis as centers.To construct an ellipse using the foci method, use this table:StepAction1Lay out horizontal (AB) and vertical axes (CD) that intersect atright angles (0).2Locate the foci (F, F’) by setting the compass to one half distanceof the major axis AB and striking arcs along AB using C as thecenter.3Mark a minimum of five equal distances between F and 0. Themore distances marked, the more accurate the ellipse construction.4Set the compass for the distance from A to 1. Strike arcs above andbelow line AB using 1 and F’ as centers.5Set the compass for the distance A to 2. Strike arcs above andbelow AB using 2 and F’ as centers. Continue plotting points thisway until all five points form an ellipse circumference between CBand BD.67Mark a minimum of five equal distances between 0 and B.Plot the five points forming an ellipse circumference between CAand AD using the same previous procedure but in reverse using Fas the center.8Once all points are plotted, connect the points using french curves.Continued on next page2-47

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