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CATIA geometry (lines, planes, curves, etc.) is based on standard geometric constructions (as are most CAD systems). This type of geometric techniques is called "Euclidean" since it is based on Euclid's primary principles for geometry. These geometric shapes are typically planar.
The Geodesic option appears many places in CATIA; it creates geometry that lies on a curve or curved surface.
You can find more about these two methods on Wikipedia.
So, the Point On a Curve command uses the Geodesic mode for the Distance On Curve and Ratio of Curve Length, and the Euclidean option is only available for Distance Along Direction.
You can find more about these options in the CATIA Online HELP.