Hello all, sorry for the noob posts, I'm relatively new on Houdini (but learning fast). Searching the forums is great help, but sometimes either I can't quite find the answer, or the thread isn't clear enough.

My questions are about scale for my scenes. I'm working on a sci/fi project so everything takes place in space and it would be quite large in the real-world.

I read somewhere that scale is important in Houdini, however there has to be a point where I can't make objects as large as their real-world counterparts.

Question 1: I'm modeling Jupiter. Is scale important? For the most part it's just a textured ball that's hanging in the background, and I might use it to generate some BG plates as needed. How large does it have to be, or can it be just 1m if need be?

Question 2: I'm modeling my spaceship. At some point I will need to blow it up with pieces/parts bursting out and floating apart. Same question, how critical is size to an object where actual physical effects will happen (i.e. Pyro, destruction, etc)?

Many thanks.

Scale is completely arbitrary. The only thing that matters is the ratios of distances and sizes. As for physical properties such as constants of gravity/spring rates/mass, the solvers are never accurate enough to where you can simply insert numbers for a table and get perfect results (gravity is an exception, but some types of simulation would need so many substeps for true gravity to be used that it effectively is an artist control). Even if everything is modeled to scale with all true masses used, there are numerous values used by solvers that have no physical basis, and must be changed by eye. So I say, use whatever scale works best for your situation. Often floating-point precision is more of a consideration when deciding a scale, so try to avoid really big and really small numbers.

Ok, great. Now for a follow up question, can a too large of a scale cause instability in Houdini? I have modeled my spaceship at real-world scale (i.e. about 800 meters long, which has been causing some headaches needing to change the clipping planes in the cameras and viewport. That project has been pretty crash-prone and I wonder if I should consider re-sizing all my geometry to a more contained size (thinking about 1/10th or less).

That range shouldn't be a problem. If you have ‘small’ things that are much much smaller than the large object in your scene, you might consider locating the small objects that have to be close to camera near the origin, and counter-moving the ship so the relative position stays the same. If you are using object-level transforms for all layout, it shouldn't be an issue. However, when applying transforms in sop-level, precision issues can crop up.

For example, on recent project, the layout consisted of a tall building with a camera near the top of the building, outside a window. The fx consisted of a number of small pebbles (mm sizes). If I had animated the fx in their world space position, a loss of precision large enough to be visible could occur. To prevent this, I parent the structure and camera to an offset transform, to move the action to as close to the origin as possible.