# Creating surface meshes

This exercise uses PDAL to create surface meshes. PDAL is able to use a number of meshing filters: https://pdal.io/stages/filters.html#mesh. Three of these are ‘in the box’, without needing plugins compiled. These are 2D Delaunay triangulation, Greedy projection meshing and Poisson surface meshing.

In this exercise we’ll create a Poisson surface mesh - a watertight isosurface - from our input point cloud.

## Exercise

We will create mesh models of a building and its surrounds using an entwine data input source.

After running each command, the output .ply file can be viewed in Meshlab or CloudCompare.

PDAL implements Mischa Kazhdan’s Poisson surface reconstruction algorithm. For details see [Kazhdan2006]_

Note

writers.ply will write out mesh vertices by default. In this exercise we set the attribute faces=”true”. Try using the ply writer without it. Also, if you’re using a machine with a lot of processing power, try increasing the depth parameter for a more detailed mesh.

### Command

Invoke the following command, substituting accordingly, in your Conda Shell:

```1pdal translate -i ept://http://act-2015-rgb.s3.amazonaws.com \
2 -o ./exercises/analysis/meshing/first-mesh.ply \
3 poisson --filters.poisson.depth=16 \
5 --verbose 4
```
```1pdal translate -i ept://http://act-2015-rgb.s3.amazonaws.com ^
2 -o ./exercises/analysis/meshing/first-mesh.ply ^
3 poisson --filters.poisson.depth=16 ^
5 --verbose 4
```

You can view the mesh in Cloud Compare, you should see something similar to

### Filtering

If we want to just mesh a building, or just terrain, or both we can apply a range filter based on point classification. These data have ground labeled as class 2, and buildings as 6.

In this exercise we will create a poisson mesh surface of a building and the ground surrounding it, using the same data subset as above and adding a filters.range stage to limit the set of points used in mesh creation.

### Command

Invoke the following command, substituting accordingly, in your Conda Shell:

```1pdal translate -i ept://http://act-2015-rgb.s3.amazonaws.com \
2 -o ./exercises/analysis/meshing/building-exercise.ply \
3 range poisson \
4 --filters.range.limits="Classification[2:2],Classification[6:6]" \
5 --filters.poisson.depth=16 \
```1pdal translate -i ept://http://act-2015-rgb.s3.amazonaws.com ^