# Tag Info

Accepted

### Confusion about notation in a paper

The notation $\delta_{i,j}$ is the Kronecker delta, a notation commonly used in physics. It's defined as: $$\delta_{i,j} \equiv \begin{cases}1,&i=j\\0,&i\neq j\end{cases}$$ So, as you ...
• 25.1k

### Need a reputable source for the formula for the shape of Earth's horizon

The curve you are seeking is just the intersection of a plane (the back of the camera) and a right circular cone. This is not really a question about the earth, or views of planets from space; it's ...
• 348
Accepted

### How would I create a virtual cabling system?

The shape you’re trying to draw is called a catenary: it’s the shape that a cable/cord of constant density takes when supported at each end. You’ll have to do some research to find a parametric ...
• 2,222
Accepted

### Finite difference wave equation shown in paper is wrong?

Yes, it looks like a sign error in the paper. It looks like it was introduced in equation (4) and then carried through the following ones. Probably the authors wrote the source code first and the ...
• 25.1k

### How to record N-body simulation as a video?

user1118321's suggestion is the correct one but i'll elaborate a bit. You run your simulation giving it a fixed time step between frames. This time step would be 1/30th of a second (33.3333 ms) for ...
• 7,801

### Does MRG32k3a compare well with PCG and Xorshift256*?

Short answer is yes. MRG32k3a has withstood the test of time, much more than PCG or XorShift256*. In fact, a recent paper by Matsumoto (creator of Mersenne-Twister) shows some poor properties of ...
• 131

### Conserving Mass in Liquid Simulation

From your code snippet and your result for 2x2 example, I can see that you are actually simulating a domain with only Neumann boundary conditions (slip wall). In this case, the system contains a null ...
Accepted

### What is the difference between particles system and smoothed particles hydrodynamic?

Particle systems are used in graphics to represent phenomena like fire, smoke, fog, sparks, splashes, small bits of debris like rocks, splinters, or leaves, as well as magic or sci-fi effects like ...
• 25.1k

### Problem when performing IFFT for Tessendorf's ocean waves

I found the problem. Maybe this answer helps someone since there isn't much discussion on the topic. I was doing the following change of coordinates in the frequency domain to fit the values on the ...

### What exactly is it about reality that is so difficult to recreate in a 3D simulation?

As @AnnoyinC already mentioned in his comment, we are simply lacking computational power and storage requirements (RAM). For the visual effects, you need to calculate every ray of light that somehow ...
• 1,251
1 vote

Your second shader reads 10x10 pixels of data and writes 8x8 (which is correct), however, it handles corner and edge cases with lots of "if"s. This leads to divergence and kills performance. ...
• 11
1 vote
Accepted

### Represent shape as particles

Solution: Check for the minimum x,y,z value for all points. Add these values multiplied by (-1) to all points in order to guarantee that all points are not negative. Then take the largest point and ...
1 vote

### How to record N-body simulation as a video?

You could always write each frame out as an image and then use another tool to compress it into a movie that you playback. You don't say what type of system you're running on, but I believe that ...
• 3,421
1 vote
Accepted

### Cloud simulation software

There are a couple of companies doing middleware cloud simulation and rendering. It might have been SilverLining by Sundog, or trueSKY by Simul.
• 25.1k
1 vote
Accepted

### kinematics and dynamics of a sphere in a spring mass system?

The rigid body simulation is very similar to the point mass case except for that we have to handle rotational motion (orientation and angular momentum). In addition to common particle attributes such ...
1 vote
Accepted

### Spring damping in Energy Function

The damping force you mentioned $f=-k \frac{\dot{l} \cdot l}{|l|} \frac{l}{|l|}$ is a special case of $f=-k \dot{C} \frac{\partial C}{\partial \mathbf{x}}$. Let  \begin{align} C(\mathbf{x}) &= \...
1 vote

### Components that can be used for 3d shadow analysis, sunhours of surfaces throughout the year in a 3d model?

I use Nvidia OptiX for Ray casting and tracing purposes. It is based on CUDA and gives you a library that runs on GPU and is capable of building and traversing efficient acceleration structures. You ...
• 1,810

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