3. Calculating and Saving Velocities - isathar/Blender_UE4_VectorFieldEditor GitHub Wiki

The editor can retrieve or calculate velocities from different sources and blend them with stored velocities using several user-selectable methods.

Velocities can be modified in steps, allowing you to perform vector math operations or blend new values with the saved velocity list.

More information on velocity types and blend methods here.

  • To calculate velocities, you need to select the vector field (the VF_Volume_x object that contains the points) you're working on first.

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Usage:

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Getting Velocities from the Particle System:
  1. Create some forces in the scene to influence the vector field
  2. Select the vector field volume and go to its Particle Properties
  • Customize the Particle system's Physics and Rotation Settings as needed
  1. (Optional) Bake the particle system's transforms (under cache)
  • (this will speed things up when moving between frames)
  • if a bake is already active, click Free Bake
  • Baking is required if you're trying to get Angular Velocities
  1. Advance the timeline to the frame you want to get velocities from
  2. Select the Velocity Type (pick Velocity for particle velocities)
  3. Select the Blend Method, and optional parameters you want to use.
  • It's best to start out with Replace or Add to build the initial list
  1. Click Calculate
Point Velocity Mode:
  1. Place the 3D cursor at the point you want the calculation based on
  2. Select the vector field volume (if it isn't already)
  3. Select Point from the velocity mode dropdown
  4. (Optional) If you want velocities pointing towards the cursor, select Invert Next
  5. Select the Calculation mode
  • Point velocity is most effective with Average and Multiply modes
  1. Click Calculate
  • Point Mode Example Result:

img/VFCalc_PointVelResult.png

Custom Vector Mode:
  1. Select the vector field volume
  2. Select Custom Vector from the velocity mode dropdown
  3. Enter the vector value you want to use for the calculation
  4. Select the calculation mode
  • Custom Vectors are good for mathematically tweaking the current list, so Add and Multiply are good choices
  1. Click Calculate

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Example Workflow: (Vortex with Up-Pointing Velocity)

1: Add a Vortex force field (Add->Force Fields->Vortex)

img/VFCalc_Tut_AddForce.png

2: Select the vector field volume
3: (Optional) Bake the particle system's transforms
4: Advance the timeline to the frame you want to get velocities from
5: Select the Velocity Velocity Type
6: Select the Replace Blend Method
7: Click Calculate
8: (Optional) Go back to frame 0 for easier 3d line display

  • Velocity 3D lines should look something like this at this point:

img/VFCalc_Tut_RepVelocity.png

9: Select the Custom Vector Velocity Type
10: Select the Average Blend Method
11: Click Calculate

  • This will calculate the average (default weights:0.5,0.5) between the current velocity and Vector(0,0,1)
  • The result should be something like this:

img/VFCalc_Tut_AvgUpVect.png

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Invert and Normalize
  • Invert or normalize the currently saved velocities.
Examples:

Raw:

img/VFCalc_ForceEx_Raw.png

Normalized:

img/VFCalc_ForceEx_Norm.png

Normalized + Inverted:

img/VFCalc_ForceEx_Inv.png

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