Intrinsic coordinates
Intrinsic coordinates is a
coordinate system which defines points upon a curve partly by the nature of the
tangents to the curve at that point. A point is given as where
s is the length of the curve from a set point and ψ is the angle which the tangent to the curve at that point makes with the
x-axis; s = f is the
intrinsic equation of the curve.
This coordinate system has limited use, it may break down entirely when straight lines are considered, but inspection reveals three properties regarding the rate of change of its variables, namely:
Encyclopedia
Intrinsic coordinates is a
coordinate system which defines points upon a curve partly by the nature of the
tangents to the curve at that point. A point is given as where
s is the length of the curve from a set point and ψ is the angle which the tangent to the curve at that point makes with the
x-axis; s = f is the
intrinsic equation of the curve.
This coordinate system has limited use, it may break down entirely when straight lines are considered, but inspection reveals three properties regarding the rate of change of its variables, namely:
Radius of curvature
The radius of curvature, ρ, at a point is a measure of the radius of the arc which can be created by the extrapolation of that point. If this value is positive then the curve bends upwards, and if the value is negative, the curve bends downward. It is given by:
It can be proved that the following is true:
This allows the radius of curvature of a line to be found from only
Cartesian coordinates.
Another useful formula can relate the above to
parametric form:
where
Conversion
To convert a
cartesian equation y = f to an intrinsic equation, differentiate it to get dy/dx. Then find the
arc length , integrating from 0 to x. Then convert x to ψ using the dy/dx relationship above by expressing s in terms of dy/dx.