Kepler's method of dermining the orbit of Mars required the prior determination of the Earth's orbit, inferred by assuming that once each Martian year (1.88 Earth years) the planet Mars returns to the same point in space relative to the Sun, and by using trigonometry to locate the Earth given the measurable angles SEM and SME.
Repeating the above calculation of the Earth's orbit many times, with Mars in a different fixed place in its orbit, Kepler was able to deduce the orbit of Mars from the requirement that he get the same complete orbit for Earth each time.