Ellipse

P

F2

O

F1

a

b

X

Z

?

?

An ellipse is defined by:

Focal length = ?

Distance (F1, P, F2) is

constant for all points

on ellipse

When ? = 0, ellipse = circle

For the earth:

Major axis, a = 6378 km

Minor axis, b = 6357 km

Flattening ratio, f = (a-b)/a

~ 1/300

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