问.obj文件中的faces是什么?它们是如何工作的？

EN

def main():

    import re

    flt = r"-?[\d\.]+"
    vertex_pattern = r"v\s+(?P<x>{})\s+(?P<y>{})\s+(?P<z>{})".format(flt, flt, flt)
    face_pattern = r"f\s+((\d+/\d+/\d+\s*){3,})"

    vertices = []
    faces = []

    with open("alfa147.obj.txt", "r") as file:
        for line in map(str.strip, file):
            match = re.match(vertex_pattern, line)
            if match is not None:
                vertices.append(tuple(map(float, match.group("x", "y", "z"))))
                continue
            match = re.match(face_pattern, line)
            if match is not None:
                faces.append(tuple(tuple(map(int, vertex.split("/"))) for vertex in match.group(1).split()))

    print(f"The first face has {len(faces[0])} vertices:")
    for vertex in faces[0]:
        print(vertex)

    print("\nWe do not care about the texture coordinate indices or normal indices, so we get the three vertex indices:")
    for vertex in faces[0]:
        print(vertex[0])

    print("\nAfter substituting the indices for their values, the face is made up of these coordinates:")
    for vertex in faces[0]:
        print(vertices[vertex[0]-1]) # -1 because in the OBJ spec, collections start at index 1 rather than 0 

    return 0


if __name__ == "__main__":
    import sys
    sys.exit(main())

The first face has 3 vertices:
(1962, 1, 1962)
(1958, 1, 1958)
(1957, 541, 1957)

We do not care about the texture coordinate indices or normal indices, so we get the three vertex indices:
1962
1958
1957

After substituting the indices for their values, the face is made up of these coordinates:
(-4.29133, 47.755795, 51.585678)
(-4.29133, 47.716423, 51.585678)
(-4.29133, 47.716423, 52.661789)
>>>