Bifrost Scale / Units?

[Anonymous]

Hello everyone!

I am struggeling with understanding the scale and unit system of Bifrost. I read some forums and watched a lot of videos about it but I'm not really getting it, yet.

In most the videos, forums & documentations was said that Bifrost doesnt care at all about the linear Working Units in the Maya preferences because 1 unit will alway be 1 meter for bifrost.

If I have my Working Units in Maya preferences set to centimeters and I create a cube it has a scale of 1x1x1. From what I understand this means for bifrost 1 meter x 1 meter x 1 meter.

When I change the Working Units in Maya preferences of the same scene to meters and I create a second cube it is one hundred times bigger but it's scale is also 1 x 1 x 1. And I don't get how both cubes are 1 meter x 1 meter x 1 meter for bifrost.

So there must be at least some reasonable reference when creating objects. Beside messing around with the camera's clipping planes.

In a forum post someone said "Bifrost works best in the default unit of cm, but treat each unit as if it were 1m" (Source - The Area)

On the other hand Daryl Obert mentioned in the comments of this youtube video that he is always working in meters and never changing it.

In this tutorial Dave Scotland is workig with Working Units set to centimeters but since the bottle has the scale of 1 which would equal 1 meter for Bifrost he is scaling the bottle down to the scale of 0.30 which would be 30 centimeters to Bifrost.

Then again in this tutorial in the Maya Learning Channel the tutor refers to the Working Unit in the preferences as being in centimeters and therefor he is messing with the Bifrost settings to match them (setting Gravity Magnitude to 9.80 to 980 etc).

But if you open the scene files each of the buildings has a scale of 1 x 1 x 1 which might have happend by Freezing Transformations. The container has a scale of 0.413 x 0.413 x 0.399 and the emitter a scale of 34 x 4 x 65.

If I'd rescale (x100) the whole town to match the original Gravity Magnitude of 9.80 I get buildings with 100 x 100 x 100, a container with 41.3 x 41.3 x 39.9 and an emitter (which needs to be created first) of about 3419 x 628 x 6679 which means it would have an x and z scale of some kilometers within a container with the size of some meters?

I brought up everything I found about it and the issues I am having with understanding scale & units with Bifrost and I hope some people would look into it since it is very basic for the understanding of Bifrost.

Thank you and have a great time,

Alessandro

[Anonymous]

I made some more tests trying to get into the logic behind Bifrost scales & units.

I opened a new scene, went to Preferences and set the Working Units to meters. I created a cube (Scale 1x1x1) and assigned a Bifrost Liquid with default settings to it. The result were 3704348 Bifrost Particles and 5044250 Bifrost Voxels.

Doing the same in a scene with Working Units set to centimeters I got 47 Bifrost Particles and 19375 Bifrost Voxels. When I resized this cube by the factor of 100 I got exactly the same particle and voxel count like in the first scene.

I'm really not sure how to interpret this, yet, but I believe it's saying that 1 Unit equals 1 (Bifrost) Meter if the Maya Preferences in the scene where the objects were build were set to Meters. After this changing the Working Units from meters to centimeters doesn't have any effect on the simulation. I think this should be right?

The documentation (Bifröst simulations and scene scale) says:

"Many aspects of Bifröst simulations depend on the scale to which a scene is modeled. There are several settings that you may need to adjust, depending on the size of objects in the scene.

In particular, Bifröst does not consider the value that you have set for Linear in the Working Units group of your Settings preferences. The default values of attributes are instead based on the assumption that 1.0 scene unit is equal to 1.0 meter, and simulations do not change behavior when Linear is set to centimeter or anything else. [...] Another approach is to keep the scale at 1.0 scene unit = 1.0 meter, and model very large or small objects while leaving the physical attributes at their defaults."

I think I am getting it now. The Working Unit settings make a difference when it comes to creating the actual model but changing the Working Units afterwards doesn't have any effect on the Simulation itself. Having the Working Units set to 1 Meter while building your models means large scale scenes but you can use the Bifrost default settings. Because the assumption is that you have modelled everything in 1 unit = 1 meter. Having it set to centimeters while modeling you need to adjust the Bifrost settings according to the documentation.

Having this I can assume that 1 Unit equals 1 (Bifrost-)Meter only if the preferences are set to 1 Meter for the modelling or setting up/scaling of the objects. If set to centimeters then 100 Units equals 1 (Bifrost-)Meter. This was the confusing part for me.

Please correct me if I am wrong. I hope others can learn from my documented slow-wittedness

Have a great time everyone

[Anonymous]

I just checked my "Mastering Autodesk Maya 2016" (Autodesk Official Press) book and there it says on page 714:

"Bifrost liquid simulation is internally measured in meters. Maya uses centimeters as it's default unit of measurement. Therefore, 1cm is seen as 1 meter by the bitfrost solver."

Which is a kinda disturbing statement since the documentation states: "The default values of attributes are instead based on the assumption that 1.0 scene unit is equal to 1.0 meter."

I think this needs some clarification for Bifrost Beginners.