Houdini Velocity Grid Exporter

Hi, everyone!!

I made a digital asset which is able to export *.fga file from Houdini. Basically it does the same thing with the MayaVelocityGridExporter, except that you can now use Houdini’s powerful tools to generate the velocity field data. All you need to do is to wire the velocity grid exporter to your dopnetwork, specify an output path and press the export button. Current features include

  • voxel resolution adjustment
  • velocity field data from particle/fluid simulation
  • frame range selection

Houdini Orbolt website download link:

I’m new to Houdini and Unreal Engine. Also this is my first digital asset for Houdini. So any kind of feedback or comments are very welcome!

Enjoy and have fun all :smiley:

Is this a way to make the fields like in this demo video, around the 11 min mark?

Hi elindell,
Sorry to reply you so late because I was on a vocation ^^; For the the field you mentioned in the video, I think it’s not a problem to simulate that in Houdini. It seems like particle follows a spiral path. When I got some time, I can try to make a similar one in Houdini and use the tool to export the vector field then import that into Unreal Engine just like the video does. Once I’m done I’ll send you a sample file and you can try it by your own and see how it goes :slight_smile:


I made a simple simulation basically using the curve force in Houdini and make the particles followed a spiral shape like path. Then export the simulation result to an fga file and import into Unreal Engine 4. It may not seem exactly the same like the one showed in the tutorial video. But I think the idea behind is pretty much similar. Hope it helps. Thank you ^^
2014-08-25 15_28_14-C__Users_benny_yang_spiral_path_particle_2.hipnc - Houdini FX Non-Commercial.png
2014-08-25 15_27_25-test_vf_ps_.png

I want to make a vector field ad well, but I don’t want to rely on licensed software. Can you specify the file format for fga or attach an example file. What I find on the internet so far is only for 2D GRID data, but we need 3D Volume data. Thanks.

Houdini has apprentice version which is free to use and able to use the exporter to generate the fga file. it’s also possible for you to write a program to generate the fga file. The file format for fga is pretty straightforward. The first 3 field is the resolution for the whole volume, then followed by min and max bounding box and finally a bunch of velocities for each grid. The link ( is the data I used for the spiral effect test as shown above. Hope it helps. :slight_smile:

thank you very much 220225!

220225 Thanks… Too bad I spent my entire sunday trying to find an fga file, and I ended up downloading an illegal version of maya, just to follow the tutorial from unreal, just to get to know the file format. I think unreal made up the fga file format since the only other reference uses a keyword based 2D format. I am kinda annoyed that they didn’t document it… Hopefully unreal will keep investing in documentation and tools and hopefully the community will also grow that makes tools and shares results…

thats awesome, greatly appreciated. I was about to look into writing it myself, glad I found your OTL.

So it doesnt support Pyro sims for now. Im trying to workaround it by bringing my Velocity Field from Pyro to Flip object, so I can export it to FGA.

Any plans on adding Pyro support out of the box ?


You’re welcome. I haven’t played too much with Pyro so far ^^;. I’ll try if I can get this working and let you know. :slight_smile:

I uploaded a new version of the asset which supports the Pyro FX to the Orbolt website. The link is If you are interested in it, please give it a try and let me know any comments. Thank you all and have a great day :smiley:

Ok, I’ve followed the tutorial on to know the file format. I’ve made my own python script that can generate the Unreal Engine Fluid Grid ASCII file format. I believe this is a self-defined format, since I cannot find any other reference to it.

You can download the python script file at.

The code creates 3 fga files of vector fields

  • Vector field with positional coordinate entered in each voxel (so a radial vector field)
  • A cone vector field (just a section of above)
  • A vortex (cross product of Z-vector with 1st vector field)

thanks 220225! I think I got it working, but need to learn alot more about houdini :slight_smile:
quick question, for the spiral you created about what voxel size did you export it at?

Nice work isgoed!

To elindell, it’s 20x20x20. However, I think it’s too big. You don’t need so much detail for that spiral effect. After you import the data into Unreal, the editor provides you more control for the final result you want. You can simply think that the simulation is the path how you particles will follow, that’s it. Have fun all, sorry to reply a week late XD.

This is awesome!

Do you know how to use the sequences of .fga in UE4?

I hate to be the person said this, but 220225 should understand that SideFX does not allow “exporter” type of thing with apprentice license.(I contacted them before on the HD version and get the same response, no export of any kind even though you can write a plugin yourself.)
As with anyone wanted to do this themselves, be careful and always check with the software’s owner before you think you did something smart to use their software for free.

It’s unlikely that any actual game could be done just by vector field files, but everything has a starting point, and I hope you guys tread the business path carefully.

PenguinTD is right: the EULA for Apprentice allows no commercial use whatsoever, but if you bump up to Houdini Indie, it’s all good.

I wouldn’t say “all good” Houdini Indie still has very specific terms as well. Always read the EULA.

Any chance you could upload the .hip for this file? I’m having trouble getting the vectors to point in the correct direction, can’t figure out what the cause is. Would like to use it as an example if you’d be so kind :slight_smile: