helixish: make railway basis right-handed

Previously the y axis was reversed!

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/helixish.py b/helixish.py
index 88769c364f5fbbeafcd3d4098e07eba8f1c034d3..0235e5b5aaa7558be48062182663dbd5f2231a05 100644 (file)
--- a/helixish.py
+++ b/helixish.py
@@ -83,7 +83,7 @@ class HelixishCurve():
     railway_inplane_basis_x = np.hstack((q_plane[0:2], [0]))
     railway_inplane_basis = np.column_stack((
       railway_inplane_basis_x,
-      np.cross([0,0,1], railway_inplane_basis_x),
+      -np.cross([0,0,1], railway_inplane_basis_x),
       [0,0,1],
       [0,0,0],
     ))