principal normal indicatrix
principal normal indicatrix[¦prin·sə·pəl ‚nȯr·məl in′dik·ə‚triks]
For a space curve, all the end points of those radii of a unit sphere that are parallel to the positive directions of the principal normals to the curve. Also known as spherical indicatrix of the principal normal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.