week 5&6 - building destruction
/// Empire State Photogeommetry ///
For objects that are perfectly symmetrical on both sides, Postshot always shifts the camera angle from one side to the other. Even setting up the background and markers cannot completely solve this problem. As a result, details on the back of the building are completely lost, and the lighting on the front is incorrect.
In theory, setting up as many and as complex markers as possible might solve this problem, but even after setting up quite a few markers, it didn’t help. So I used only two-thirds of the cameras, sacrificing one side to get the other side perfect.
One feasible approach is to create the two sides in two separate steps, clean them up, and then merge them. However, this method has one drawback—it does not work well for objects with strong reflections. Such objects contain a large number of points inside, and after merging, these points will overlap, distorting the reflected image.
/// Building Destruction - Fracture ///
To simulate the building, the Gaussian Splat model must first be converted to a polygon model. This step is best accomplished through VDB conversion. Then proceed with the fracture processing.
polygon
outside fracture
inside fracture
affect path
In Dope: Use the “active” attribute to activate the fracturing region. Use complex constraint for the best effect. In geometryVOP, change the constraint name or type depending on fracture’s velocity. In SOPsolver, apply scatter force to the simulation.
At first, I kept getting stuck on issues with “active” and “constraint.” “Active” and “constraint” never seemed to work together as expected, or cause the fragments to break apart the way I wanted. After many attempts, I finally solved the problem. The key was the “name” attribute — specifically, after merging multiple fragments into a single object, all pieces needed to be renamed. Now the fragments will be activated and break along the path.
Use the GSOPs “splat deform” node to apply the deformation. As you can see, due to the limitations of the splat points, the edges of the fragments are somewhat blurred. Lighting and shadowing are even more challenging.
/// Building Destruction - Smoke ///
After completing the fracture, smoke needs to be added. Currently, the smoke effect isn't very satisfying; I'll improve it later. Nevertheless, the velocity field is already working correctly.
I had previously tried using pyrosolver to create smoke, but didn't get very good results. It wasn't until I looked at Triangle FX’s tutorial that I realized using smoke(sparse) solver in Dopnetwork is the correct approach.
It is really a very detailed and comprehensive guide to building destruction.
Link: HOUDINI TUTORIAL | Destruction of a Building
/// Relighting Test///
This is a re-lighting method provided by GSOPs. The principle is based on recoloring based on the distance between the light source and the GS particles. The newly released Houdini 22 includes new lighting tools, but they likely still won’t resolve the shadow projection issues. Therefore, the problem ultimately has to be solved through compositing.
/// Compositing Test ///
Compositing using only the shadow channel isn’t enough. Here, I’ve exported the following AOVs: “mask” is used to limit the range of the splat and smooth out jagged edges on the GS particles; “diffuse” is used to restore some of the fragments that were overly smoothed out; “depth” is used to enhance lighting and depth-of-field effects; and “velocity” provides a motion blur effect.
mask
splat
diffuse
velocity
compares
before&after mask
before&after motion blur
before&after motion blur
/// Next Plan ///
1. Refine the destruction scene
2. Try Houdini-22 new GS feature
3. Start Statue of Liberty shot