Houdini training day 8

Following this tutorial that creates trails from volumes.
Playing with some splines. In Houdini you create them with the Curves sop.
Resample to subdivide splines.
Polyframe to generate tangents from points.
Press X to create a Visualize node.

A nice way to invert tangents from points is with an Attribute Wrangle and this code
v@tangent = @tangent * -1;
Just be careful when declaring the type of variable. A tangent is a vector, not a float.

The Volume sop has some interesting parameters:

• Rank
• Scalar

, each voxel holds just one value.

• Vector

, each voxel holds three values.

• Matrix

, each voxel holds nine values.

If you want to use the tangents in your Volume, you have to use a Vector rank.
Careful about Name parameter of Volume sop. It’s not “just a name”. It’s absolutely important.

Naming volumes allows mantra and the Volume VOP to override the correct parameters with the values of the volume.

The input of the Volume sop is Bounding Source. It’s the Bounding Source of the geometry! When you create a Volume it will look at the boundary box of your object. If you want to increase the Volume boundary box, use a Bound sop, not a Volume Bound!

Volume Vop allows us to write vex for volumes.
When you’re working with vector, remember to change Bind export to vector!

These are Vops that I used in the Volume Vop.
Point Cloud Open: this node opens a point cloud file and searches for points around a source position.
Pount Cloud Filter: allows us to choose an attribute (channel) from the point cloud.
Length: it calculates the lenght of a vector.

Volume Trail sop: computes a trail of points through a velocity volume (from the help!).