<div id="comment:0"></div> In analogy to the existing method `normal_cone`. For #29806 (Gram-Brianchon formula) I only need the (affine) tangent cones of a face, tcone(P, F). See for example https://epubs.siam.org/doi/pdf/10.1137/1.9781611972443.ch6 Def 6.2.2 CC: @jplab @kliem @orlitzky @yuan-zhou @tscrim Component: **geometry** Author: **Matthias Koeppe** Branch/Commit: **[`5965400`](https://github.com/sagemath/sagetrac-mirror/commit/5965400139f4ff4e3a589a2d71ad8ff3674d87b1)** Reviewer: **Jonathan Kliem** _Issue created by migration from https://trac.sagemath.org/ticket/29811_