Ellipse Construction, Continued
The foci method of ellipse construction involves plotting a series of points
along the circumference of the ellipse by drawing a series of intersecting arcs
using the foci on the major axis as centers.
To construct an ellipse using the foci method, use this table:
Lay out horizontal (AB) and vertical axes (CD) that intersect at
right angles (0).
Locate the foci (F, F) by setting the compass to one half distance
of the major axis AB and striking arcs along AB using C as the
Mark a minimum of five equal distances between F and 0. The
more distances marked, the more accurate the ellipse construction.
Set the compass for the distance from A to 1. Strike arcs above and
below line AB using 1 and F as centers.
Set the compass for the distance A to 2. Strike arcs above and
below AB using 2 and F as centers. Continue plotting points this
way until all five points form an ellipse circumference between CB
Mark a minimum of five equal distances between 0 and B.
Plot the five points forming an ellipse circumference between CA
and AD using the same previous procedure but in reverse using F
as the center.
Once all points are plotted, connect the points using french curves.
Continued on next page