Meshlab
- mohamedabdulgafoor
- Dec 31, 2020
- 2 min read
Viewing point clouds
1. Geometry & Attribute information.
Notepad++ is a text and source code editor, it can be installed in Windowd, Mac and Linux (using wine). It is good to open very large text files, otherwise, the normal text editors will likely to crash if the data is very large. Let's open a .obj file using Notepad++. You can see it contains the information about the vertices and the faces. For example, v 0.032027 0.056575 -0.050364 shows the vertex information. Similarly if we scroll down we will observe the faces information such as f 60497 60509 62748. All the information is stored in this file, so that we can use it to reconstruct the 3D object. Here we use triangular meshes.
On the other hand, .ply files contain information about the 3D points, not face information. For example the first data says, 223 461 255 are coordinates of the point and the 109 19 26 are the pixel information.
2. ASCII Vs Binary
ASCII stands for "American Standard Code for Information Interchange. This protocol is made up of data that is encoded in ASCII values with minimal control codes added (ref 2). On the other hand, Binary more is commonly known as BCP (Binary Communications Protocol). It has a value in the range of 0-255. Binary encoding is good for the compression.
We have opened a 3D model, made some modification and save it in two different formats to see the compactness.
We can see that the binary is more compact than the ASCII format. Also the binary format is more secure in terms of the security.
We can split the Windows into vertical/horizontal mode to work around easily. The following figure shows the vertical split.
Selecting & deleting point cloud.
We can select and delete the point clouds as we want. Now let us select the upper part of an object and delete it. The following figure shows how to select the points, and delete it. We can use the select tool from the tool bar above and choose the region to delete it. Then go to Filters --> Selection --> Deleted Selected Vertices.
Computing normal
Now let us compute the surface normal to a 3D object like in the below.
To visualize it, go to Render--> Show Normal. It will shows all the normal vectors. The following figure shows it. Depending on the surface, the normal vector will change. Some vectors will have different orientation than the others.
References:
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