I am facing some strange problem with a simple obj-file I created. The obj-file contains 8 vertices which represent the corners of a cuboid-like shape. For each of the vertices I calculate a vertex normal (which I need for rendering). The object contains 12 triangle faces which are defined by the references to the vertices and normals. The order of the vertices to define a face seems to make a difference to the normal orientation of faces. E.g. the faces
"f 2//2 1//1 3//3" and "f 1//1 2//2 3//3" might not have the same normal orientation.
Can anyone tell me, how the vertices to define a triangular face should be ordered? I have not found information about this (only that vertices are ordered counter-clockwise by default, though Im not sure what "counter-clockwise" actually means in a 3D point cloud).
I'm attaching a screenshot (used CloudCompare), which shows the obj with incorrect (top) and correct (bottom) face orientations.
.
The .obj file code I've added below. Note: the second obj only differs in the face vertex order.
Any help is very much appreciated. Thank you!
Incorrect face orientation:
v 142.275 -164.684 -222.937
v 144.341 -156.611 -189.123
v 144.475 -189.798 -192.755
v 142.505 -195.249 -224.626
v 330.045 -162.613 -234.9
v 332.11 -154.539 -201.085
v 332.245 -187.727 -204.718
v 330.274 -193.177 -236.589
vn -0.988559636 0.113057396 -0.09983923
vn -0.949405612 0.193458398 0.247392061
vn -0.965486533 -0.148224101 0.214162018
vn -0.972490893 -0.202126966 -0.11578494
vn 0.965175897 0.134606199 -0.224313751
vn 0.96863934 0.214622417 0.125200028
vn 0.98787863 -0.126679515 0.089711275
vn 0.954142849 -0.180867505 -0.238533788
f 1//1 2//2 3//3
f 1//1 3//3 4//4
f 5//5 6//5 7//7
f 5//5 7//7 8//8
f 1//1 2//2 6//6
f 1//1 5//5 6//6
f 1//1 4//4 8//8
f 1//1 5//5 8//8
f 3//3 6//6 7//7
f 2//2 3//3 6//6
f 3//3 8//8 7//7
f 3//3 4//4 8//8
Correct face orientation
v 142.275 -164.684 -222.937
v 144.341 -156.611 -189.123
v 144.475 -189.798 -192.755
v 142.505 -195.249 -224.626
v 330.045 -162.613 -234.9
v 332.11 -154.539 -201.085
v 332.245 -187.727 -204.718
v 330.274 -193.177 -236.589
vn -0.988559636 0.113057396 -0.09983923
vn -0.949405612 0.193458398 0.247392061
vn -0.965486533 -0.148224101 0.214162018
vn -0.972490893 -0.202126966 -0.11578494
vn 0.965175897 0.134606199 -0.224313751
vn 0.96863934 0.214622417 0.125200028
vn 0.98787863 -0.126679515 0.089711275
vn 0.954142849 -0.180867505 -0.238533788
f 2//2 1//1 3//3
f 3//3 1//1 4//4
f 5//5 6//6 7//7
f 5//5 7//7 8//8
f 1//1 2//2 6//6
f 5//5 1//1 6//6
f 4//4 1//1 8//8
f 1//1 5//5 8//8
f 6//6 3//3 7//7
f 2//2 3//3 6//6
f 3//3 8//8 7//7
f 3//3 4//4 8//8