Convert Sketchup SKP files to DXF or STL

代码说明：

This is a plugin script for Go-ogle"s free 3D design program Sketchup. The free version of Sketchup has limited file export options and many CAM programs will not recognise the native Sketchup (SKP) file format. This plugin allows you to export your Sketchup model as a DXF or STL files readable by most CAM and 3D printer software.Using the pluginAfter copying this file, start Sketchup and you should now have an extra menu option (Export to DXF or STL) in the Sketchup Tools menu.There are five export options:STL  triangles. Use this for Makerbot or Reprap style 3D printersDXF polyface mesh. This will give the most faithful reproduction of your original Sketchup model.DXF polylines: exports the outlines of each face as a polyline, sometimes useful for CAM toolpaths.DXF triangular mesh: breaks all the faces up into trianglesDXF lines. This