Dear @Philipp Oeser (lichtwerk) , thanks for your answer. Yes, you are right in some places I have gaps in the mesh, that's why positions were wrong. But in most cases 3D positions are almost correct, I get deviations from correct positions in ~cm or ~mm range. After careful debugging, I have noticed, this happens due to place in file "blender/intern/cycles/kernel/geom/geom_triangle_intersect.h", line 221:
May 2 2018
Apr 30 2018
Dear @Brecht Van Lommel (brecht) , thanks for your advice. Yes, you are right I had anti-aliasing issue. After choosing following settings to switch off AA, positions at the edges were correct.
Apr 27 2018
Thanx for investigating.
Could you please attach a .blend as well so someone can reproduce with your geometry?