Some remarks on the visual angle metric
  We show that the visual angle metric and the triangular ratio metric are comparable in convex domains. We also find the extremal points for the visual angle metric in the half space and in the ball by use of a construction based on hyperbolic geometry. Furthermore, we study distortion properties of quasiconformal maps with respect to the triangular ratio metric and the visual angle metric. 
Parisa Hariri, Matti Vuorinen, Gendi Wang
math.MG