# Mesh Manipulation with Blender
Blender is a useful alternative to Rhino for working with meshes: **rebuilding meshes** (decimate geometry), splitting models, filling holes and to smoothing (auto shade) meshes.
## 2.0 Useful Resources
### 2.1 Clean Up
#### 2.1.1 Decimate Geometry
**Decimating Geometry** performs a similar function to Rhino 3D's `ReduceMesh` command.
This function is useful to **reduce the number of faces/vertices** of a mesh. A surprising number of vertices can be removed without affecting the quality of a 3D print. This can be extremely useful in reducing the file-size of your mesh.
Use the **Decimate Modifier**, available in the **Modifiers** drop-down.\
`Select Mesh > Properties Region > Settings Icon > Add Modifier > Decimate Geometry`
Change the `ratio` field to **reduce** the number of **Mesh Faces**. A Ratio of **0.1** will reduce the number of faces by **90%**.
**Click** `apply` once the changes are satisfactory.
See the [Tutorial below](https://www.youtube.com/watch?v=W9B43k9EWVM) for more information:
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Figure 2.1.1 - Decimate Modifier Blender Tutorial (Source: Yan Sculpts)
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#### 2.1.2 Fill Holes
Blender is extremely good at filling in holes to convert an open mesh in to a closed mesh
Useful to fill in small holes (open faces) in a mesh.
#### 2.1.3 Make Faces Planar
**Planarizer** is an Add-On for Blender which can be downloaded from [GitHub](https://github.com/Klowner/blender-planarizer).
**Planarizer** allows a user to select **individual mesh faces** (quads or tri's) and their **vertices**. A **Plane** is constructed from the position of these vertices. When the **planes of adjacent quads do not align** (are not parallel) these faces are said to be **non-planar** or non-co-planar.
Once **Planarizer** has been **installed**, use the `W` key to open up the **Specials Menu.** From this menu, **select Planarizer**.
**Select the vertex** which is out of alignment, click `w > planarizer` and then in the `Mesh Tools > Planarizer` menu, **select** `Anchor To: Connected Vertex`.
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The **Planarizer** algorithm works best if the user **works away from the 3d cursor** (starting at the edge closest to the cursor and moving away from that point).
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See the [Tutorial below](https://www.youtube.com/watch?v=XYROkaygnys) for more information:
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Figure 2.1.3 - Blender Planarizer (Source: Mark Riedesel)
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#### 2.1.4 Split Model (Bisect Tool)
1. Ensure Blender is currently in **Orthographic View** `[Numpad: 5]`
2. Switch in to **Edit Mode** `Tab > Edit Mode`
3. Select the **Bisect Tool** `Tools > Add > Bisect`
4. Draw a line as desired through the model
5. **Check** the **Fill option** `Plane Normal > Fill`
6. Select the **Inner Region** `Select > Select Loop Inner Region`
7. **Seperate** the **currently selected object**. `P > Selection`
See the [Tutorial below](https://www.youtube.com/watch?v=-QfLdbzSZdw) for more information:
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Figure 2.1.4 - Blender Bisect (Source: Gamemaker Game Programming Course)
{% endembed %}
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**Note**: Model will only be a shell and needs to be made solid prior to 3D printing
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#### 2.1.5 Delete Loose Geometry
Occasionally in the process of generating meshes using software packages such as Rhino 3D, **disjoint meshes** can be created. It can be difficult to spot the disjoint faces which may be floating far from the rest of the geometry.
These disjoint or **disconnected** **meshes** can cause problems when trying to import a mesh in to a printer software - as the software may think the **object is too large to print**.
**Blender** is the perfect software to **remove loose faces**.
In `[Edit Mode]` go to `[Menu], [Clean up], [Delete Loose]` to **remove unconnected** and unwanted **vertices** and **edges** and **faces** if needed.
#### 2.1.6 Dissolve Degenerates
**Degenerate faces** are **polygons** with **an area of zero (0)**. A **polygon** is constructed as a **face between three or more points**. **Degenerate faces** are polygons which have been constructed as a face between **one or two points**. These faces can result in errors when the model has been created for 3D Printing.
**Blender** can easily **remove degenerate faces**.
In `[Edit Mode]` go to `[Menu], [Clean up], [Degenerate Dissolve]` to delete edges of 0 length and faces with 0 area.
**For more information** refer to the [Blender Manual](https://docs.blender.org/manual/en/latest/modeling/meshes/editing/cleanup.html):
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### 2.2 Smoothing
**Smoothing** can be used to create softer **geometries**.
**Autosmoothing** is a simple method of **smoothing by splitting edges** . This creates **less featured** (facetted) meshes. In Blender Auto Smooth can be enabled in `Panel > Properties editor > Object Data`. The **Angle** can be changed for more or less aggressing smoothing.
#### 2.2.1 Smooth
In `[Edit Mode]` go to `[Menu], [Mesh], [Vertices], [Smooth Vertex],` to smooth sharp edges. This is done by averaging the angles between different faces. Amount of smoothing can be controlled by selecting number of iterations of smoothing.
#### 2.2.2 Laplacian Smooth
In `[Edit Mode]` press`[w]`, select `[Laplacian Smooth]`to smooth sharp edges.
**Laplacian smoothing** operations **preserve the original shape of the item better**, while also smoothing mesh surfaces satisfactorily. Laplacian smoothing uses the following algorithm:
$$
{\displaystyle {\bar {x}}*{i}} = \frac{1}{N} {\sum*{j=1}^{N}{}}{\bar {x}}\_{{j}}
$$
> Where is the number of adjacent vertices to node,  is the position of the -th adjacent vertex and is the new position for node.
**For more information** on Smoothing using Blender, refer to the [Blender Reference Manual](https://easyblend.org/html/modeling/meshes/smoothing.html):
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## 3.0 Other Resources
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Figure 3.0 - 3D Filters in Blender (Source: Thomas Sanladerer)
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