使用开源OpenCTM进行常用三维格式互导
1. 支持导入的三维格式有：
OpenCTM(.ctm)、Stanford triangle format(.ply)、Stereolitography(.stl)、3D Studio(.3ds)、COLLADA(.dae)、
Wavefront geometry file(.obj)、LightWave object(.lwo)、Geomview object file format(.off)
2. 支持导出的三维格式有：
OpenCTM(.ctm)、Stanford triangle format(.ply)、Stereolitography(.stl)、3D Studio(.3ds)、COLLADA(.dae)、
Wavefront geometry file(.obj)、LightWave object(.lwo)、Geomview object file format(.off)、VRML 2.0(.wrl)
3. 纹理贴图格式：JPEG、PNG
4. 使用命令行工具ctmconv.exe进行批量转换
示例：ctmconv Infinite-Level_02.3ds Infinite-Level_02.obj
详细参数如下：
Usage: ctmconv infile outfile [options]
Options:
Data manipulation (all formats)
--scale arg Scale the mesh by a scalar factor.
--upaxis arg Set up axis (X, Y, Z, -X, -Y, -Z). If != Z, the mesh will
be flipped.
--flip Flip triangle orientation.
--calc-normals If the source file does not contain any normals, calculate
them.
--no-normals Do not export normals.
--no-texcoords Do not export texture coordinates.
--no-colors Do not export vertex colors.
OpenCTM output
--method arg Select compression method (RAW, MG1, MG2)
--level arg Set the compression level (0 - 9)
OpenCTM MG2 method
--vprec arg Set vertex precision
--vprecrel arg Set vertex precision, relative method
--nprec arg Set normal precision
--tprec arg Set texture map precision
--cprec arg Set color precision
Miscellaneous
--comment arg Set the file comment (default is to use the comment
from the input file, if any).
--texfile arg Set the texture file name reference for the texture
(default is to use the texture file name reference
from the input file, if any).
Supported file formats:
OpenCTM (.ctm)
Stanford triangle format (.ply)
Stereolithography (.stl)
3D Studio (.3ds)
COLLADA 1.4/1.5 (.dae)
Wavefront geometry file (.obj)
LightWave object (.lwo)
Geomview object file format (.off)
VRML 2.0 (.wrl) - export only