使用Meshlab的心得

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使用Meshlab的心得

2015年4月1日 | 电脑知识, 程序设计 | 没有评论

MeshLab处理模型的几个学习心得:

1 如何删除3D物体内部的面,针对格式包括3DS, OBJ等

参考页面:

http://meshlabstuff.blogspot.com/2009/04/how-to-remove-internal-faces-with.html

How to remove internal faces with MeshLab

A very common situation that often arise the cleaning of a model with a detailed interior in
which you are not interested in (and you want to remove it once for ever!). For example consider this nice LEGO model: 200k faces. Most of the faces are hidden inside the model, used to describe the internal pieces and pegs: not very useful in most cases. We can remove them with MeshLab.

After starting the filter color->vertex ambient occlusion over the mesh (and after waiting a few seconds) we have computed both a per-vertex gray color and stored for each vertex an attribute with a occlusion value. Side note: MeshLab has a general purpose per vertex and per face scalar quantity that are used and interchanged by many different algorithms with a variety of different semantic; we call this scalar quantity “quality” for no good reason (lazyness), it is ageneric scalar quantity, it could be occlusion value (like in this case), a geodesic distance from border, gaussian curvature.

Second note: Ambient occlusion greatly enhance the perception of 3D shapes! Nowadays everyone recognizes it, but a few years ago not a lot of people was really aware of that (I am a proud user of AO since 2001 for nice renderings of Cultural Heritage stuff 🙂 and, more recently, for nice renderings of molecules ).

Back to the topic of removal of internal faces.

We now can exploit this per-vertex occlusion value to select all the faces that have all their three vertices with a very low occlusion value. That means that we remove all the faces that has no visible vertices. This is not an perfect solution, there are easy counter-examples where this approach could remove visible faces (but with hidden vertices): in most cases it works wells but a bit of caution is always recommended.

In the side figure you can see the select by vertex quality filter in action with the all the selected internal faces: 130k faces out of 200k were totally internal and can be safely removed leaving just 70k faces.

删除物体的面之后导出之前要对模型进行修复和缝合的动作。

2 如何将物体生成点云

参考页面:http://en.wikiversity.org/wiki/MakerBot/Cleaning_Up_Point_Cloud_Meshes_in_Meshlab_For_3D_Printing

 

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