> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to select random points from a Point List by filtering with volume

## Objective:

Learn how to create a selection of random points from a List of Points by using surface roughness to filter the points based on volume.

## Note:

To start, you will need to download and [import](https://support.ntop.com/hc/en-us/articles/360060151133) the [Custom Block: Filter Points by Volume.](https://ntopology.box.com/s/il5rcwaookyvphj2h7mv16zxecjblqaz)

## Procedure:

**1. Set-up:**

* [Import](https://support.ntop.com/hc/en-us/articles/360049994434) your part,
* Convert it to a mesh
* Input your mesh into a **Remesh Surface** block to create an even mesh

**2. Create Random Points**

* Add the block **Random Points on Mesh**
  * Set the spacing and amount to your desired value

![A mesh with the Random Points on Mesh block applied.](https://files.learn.ntop.com/help-articles/implicit-modeling/360099953474.png)

**3. Create the Volume to filter with**

Since we are filtering by volume, we want to create a volume that randomly covers some of the points. There are a few methods to do this with the different noise blocks such as **Simplex Noise**, **Cellular Noise 3D**, and **Surface Roughness**.

* Add a **Surface Roughness** block
* Insert your model as the Body
  * Edit the Roughness frequency, amplitude, and seed value to change your results

![The same mesh and random points as above. The implicit body used to generate the mesh is overlayed. The implicit has a texture applied using the Surface Roughness block.](https://files.learn.ntop.com/help-articles/implicit-modeling/1500001053502.png)

**4. Filter the points**

* Add the **Filter Points by Volume** block
  * Use the Surface Roughness as the Volume input
  * Set the Region to Outside

![The mesh with overlayed textured implicit. A Filter Points by Volume block is applied to isolate the points that are outside of the textured implicit body.](https://files.learn.ntop.com/help-articles/implicit-modeling/1500001131741.png)

**5.** **Optional: Create a list from the remaining points**

* Duplicate the **Filter Points by Volume** block
  * Set the Region to Inside to create the opposite selection of Points

And that's it! You've successfully created two random selections from a list of Points.

Are you still having issues? Contact the [support team](https://support.ntopology.com/hc/en-us/requests/new), and we'll be happy to help!

## Download the Example file:

* [Example file](https://files.learn.ntop.com/Support%20Article%20Example%20Files/Knowledge%20Base/Implicit%20Modeling/Filter%20Points%20by%20Volume%20Example.ntop)
* [Custom Block - Filter Points by Volume](https://files.learn.ntop.com/Support%20Article%20Example%20Files/Knowledge%20Base/Implicit%20Modeling/CB%20-%20Filter%20Points%20by%20Volume.ntop)

## Keywords:

*mesh surface texture volume list points selection filter point roughness random how-to*