In differential geometry, the tangent indicatrix of a closed space curve is a curve on the unit sphere intimately related to the curvature of the original curve. Let γ ( t ) {\displaystyle \gamma (t)} be a closed curve with nowhere-vanishing tangent vector γ ˙ {\displaystyle {\dot {\gamma }}} . Then the tangent indicatrix T ( t ) {\displaystyle T(t)} of γ {\displaystyle \gamma } is the closed curve on the unit sphere given by T = γ ˙ | γ ˙ | {\displaystyle T={\frac {\dot {\gamma }}{|{\dot {\gamma }}|}}} . The total curvature of γ {\displaystyle \gamma } (the integral of curvature with respect to arc length along the curve) is equal to the arc length of T {\displaystyle T} .
References Solomon, Bruce (January 1996). "Tantrices of Spherical Curves". The American Mathematical Monthly. 103 (1): 30–39. doi:10.1080/00029890.1996.12004696. ISSN 0002-9890.
