使用 Python 生成 Wavefront obj 文件

一位用户正在尝试使用 Python 3.3 生成一个 Wavefront obj 文件，该文件包含一个由规则间隔的顶点组成的简单三角形网格。该算法只适用于来自地球高分辨率卫星扫描的规则间隔点。用户使用大约 340000 个点，并在每个顶点四边形之间创建 2 个三角形。该代码在 Blender 或 MeshLab 中导入时似乎可以工作，但存在一个问题：沿着 x 轴的相邻面条带似乎没有连接。

解决方案

用户最终解决了这个问题。问题不在于他的网格生成程序，而在于 Blender 和 MeshLab 等 3D 程序在顶点坐标过大时会做出一些奇怪的事情。如果将真实世界地理投影坐标减少到较小的相对坐标，一切都会正常工作。事实证明，Wavefront obj 格式对数字的字节大小限制太多。或者更确切地说：常见的 3D 程序不希望数字像现实世界中的数字那么大。这样，它们以一种令人困惑的方式解释了它们得到的东西。

代码例子

用户提供的代码如下：

def simpleTriangMesh(verts):
    printAll("--creating simple triangulated mesh", "\n")
    maxCoords = [max(verts[0]), max(verts[1]), max(verts[2])]
    minCoords = [min(verts[0]), min(verts[1]), min(verts[2])]
    printAll("max. coordinates (xyz): \n", maxCoords, "\n")
    printAll("min. coordinates (xyz): \n", minCoords, "\n")

    xVerts = 0 # amount of vertices in x-direction
    yVerts = 0 # amount of vertices in y-direction
    faceAmount = 0 # amount of required faces to skin grid
    i = 0
    temp = verts[0][0]
    while(i < len(verts[0])):
        if(temp < verts[0][i]):
            yVerts = int(i)
            break
        temp = verts[0][i]
        i += 1
    xVerts = int(len(verts[0]) / float(yVerts))
    faceAmount = ((xVerts - 1) * (yVerts - 1)) * 2
    printAll("vertices in x direction: ", xVerts, "\n")
    printAll("vertices in y direction: ", yVerts, "\n")
    printAll("estimated amount of triangle faces: ", 
             faceAmount, "\n")

    printAll("----generating vertex triangles representing the faces", "\n")
    # list of vertex-index quadrupels representing the faces
    faceList = [[0 for line in range(0, 3)] for face in range(0, int(faceAmount))]
    f = 0
    v = 0
    # rather to draw hypotenuse of the triangles from topleft to bottomright 
    # or perpendicular to that (topright to bottomleft)
    tl = True # the one that changes in y-direction
    tl_rem = False # to remember the hypotenuse direction of the last topmost faces
    while(f < len(faceList)):
        # prevent creation of faces at the bottom line
        # + guarantees that v = 1 when creating the first face
        if(( v % yVerts ) == 0):
            v += 1
            tl = not tl_rem
            tl_rem = tl

        if(tl):
            faceList[f][0] = v
            faceList[f][1] = v + yVerts
            faceList[f][2] = v + yVerts + 1
            f += 1
            faceList[f][0] = v
            faceList[f][1] = v + yVerts + 1
            faceList[f][2] = v + 1
        else:
            faceList[f][0] = v
            faceList[f][1] = v + yVerts
            faceList[f][2] = v + 1
            f += 1
            faceList[f][0] = v + 1
            faceList[f][1] = v + yVerts
            faceList[f][2] = v + yVerts + 1

        f += 1
        v += 1
        tl = not tl

    printAll("----preparing obj-file-content for export", "\n")
    rectMesh_Obj = "" # string containing the mesh in obj-format (ascii)
    tempVerts = ""
    tempFaces = ""
    row = 0
    while(row < len(verts[0])):
#         temp = ("v" + " " + str(verts[0][row]) + " " + str(verts[1][row])
#                 + " " + str(verts[2][row]) + "\n")
        temp = ("v" + " " + str(verts[0][row]) + " " + str(verts[2][row])
                + " " + str(verts[1][row]) + "\n")
        tempVerts += temp
        row += 1
    row = 0
    while(row < len(faceList)):
        temp = ("f" 
                + " " + str(int(faceList[row][0]))
                + " " + str(int(faceList[row][1]))
                + " " + str(int(faceList[row][2]))
#                 + " " + str(int(faceList[row][3]))
                + "\n")
        tempFaces += temp
        row += 1
    rectMesh_Obj += tempVerts + tempFaces
    return(rectMesh_Obj)

vertsExample = [[3334, 3333, 3332], [2555, 2554, 2553], [10.2, 5.2, 6.7]]