Square Particles

[Shanta Plansinis]

HelloTodiloo,

To achieve your result, I recommend using Line output, otherwise, quad output with alpha clipping is fine.

Note that the line output will always look the same width if you soom in/out.

Thank you. Do you happen to have any resource for actually doing anything with the lines in terms of graphics. You have answered my other post about glowing particles but can the same be achieved here? I could not really find any helpful descriptions in the particle line documentation page.

I am a more-than-beginner to imageJ. I am using Fiji. I am trying to analyse (many) pictures of a square on the ground taken from above but not horizontally, resulting in distortion. I want to analyse the proportion of the image covered with vegetation, I thus need to straighten the image to have an accurate measurement. As the particle measurements will count pixels, the pixels of the final image should not be distorted.

As far as I understand the problem you want to apply image rectification. I guess if you take a plane picture of the square you could find the transformation which maps this image to the plane picture of the square.

But to do so you need to know the intrinsic parameters of the camera, which means you have to do a camera calibration. And there seems to be some radial distortion in your images which should be corrected too.

If it is possible I would try a fixed imaging set up where the reference square is above the ground and the camera has always the same distance and rotation relative to the square. Then the results can be compared without any reconstruction and the segmentation of the blue square and the red wires, which currently are partly covered), will be much easier.

If you have a systematic error (angle, lens, etc.) it makes definetely sense to calculate the distortion parameters but I guess you have very different fotos and the described method is one of the fastest and I think sufficient to estimate the vegetation cover.

Maybe I wasn't clear enough. Pay close attention to the particle settings and notice the opacity map. The money pre-comp I made was 400 X 400 and the path animated to give the bill different shapes over time. I also rotated the money layer. The particle is set to use the Texture time from Start so each new particle will have the same motion as the master money layer. If the layer used for the particle is not animated then the particle will stay the same shape. Notice the edit to the opacity map also. This prevents the money from having different opacities over time.

If you change from a Textured Square to a Textured Disk you can add in rotation to the particles. Changing the texture time also changes the orientation of the particles based on the time the particle is created.

There are lots of parameters. You just need to start fiddling with them. You should also take a look at the CC particle World documentation. It's a little hard to find but the online user guide for AE has a link to the documentation for all of the Cycore (CC) effects bundled with After Effects. You'll find the info here: _ccfx.php

I'm simply trying to make a closeup of sand in this shot. Using a collection in place of hair in the particle system in Blender, I thought I could create some realistic sand shots. However, I keep finding these square gaps. After some looking around I found most of these particles are under the mesh in these square patches. I know it's only present in the ridges of the plane mesh but I want to know how to get rid of these gaps.

I switched from rendering Object to Path and found the hair looked normal... but when I looked at the plane from below, some hairs were a bit more sticking out than others - and also clearly in patterns related to the faces. It's just not so obvious from above because the hair is so long.

Going back to Object I saw this was true for the icospheres as well - in parts where they were missing on the top side, they were visible from below. So I wondered what is wrong with those faces and the simple answer is, by displacing them they became non-planar and that makes the particles spawn below the surface if the deformation is too strong.

The solution, I selected all faces. Not just the ones in the group, since particles are getting spawned on adjacent faces to the group vertices too - but it would have been sufficient to select the group vertices and expand the selection by Ctrl+Numpad +. From the Mesh menu I then chose Clean Up > Split Non-Planar Faces.

I found that a Max Angle of 5 seemed to be sufficient for the most part, but to be on the safe side you can set it much lower. Of course you could simply split all of them, but maybe you want to generate as few polygons as possible.

After I did this, the particles showed up everywhere and none of them were placed below the surface. In general I think if you simply had a higher resolution on the mesh the effect would be much less visible, but the larger the faces and the higher the angle of deformation, the more obvious it becomes. Without splitting the faces, scaling the object down on the Z axis to flatten it would have helped for distributing the particles, but of course then the landscape would be too flat ;)

Create a particle system as a child of the sprite. Set it to create particles in world space, so spawned particles don't move when the system itself moves. That creates a "trail" effect like you see here.

Then create a looping timeline to create an animation to move the position of the particle effect around the sprite in any paths you want. A timeline can also be used to control any other settings of particle effects over time, which allows you to sequence some really neat choreographies for them.

Although we endeavor to make our web sites work with a wide variety of browsers, we can only support browsers that provide sufficiently modern support for web standards. Thus, this site requires the use of reasonably up-to-date versions of Google Chrome, FireFox, Internet Explorer (IE 9 or greater), or Safari (5 or greater). If you are experiencing trouble with the web site, please try one of these alternative browsers. If you need further assistance, you may write to he...@aps.org.

We study the inertial migration of finite-size neutrally buoyant spherical particles in dilute and semidilute suspensions in laminar square duct flow. We perform several direct numerical simulations using an immersed boundary method to investigate the effects of the bulk Reynolds number Reb, particle Reynolds number Rep, and duct to particle size ratio h/a at different solid volume fractions ϕ, from very dilute conditions to 20%. We show that the bulk Reynolds number Reb is the key parameter in inertial migration of particles in dilute suspensions. At low solid volume fraction (ϕ=0.4%), low bulk Reynolds number (Reb=144), and h/a=9 particles accumulate at the center of the duct walls. As Reb is increased, the focusing position moves progressively toward the corners of the duct. At higher volume fractions, ϕ=5%, 10%, and 20%, and in wider ducts (h/a=18) with Reb=550, particles are found to migrate away from the duct core toward the walls. In particular, for ϕ=5% and 10%, particles accumulate preferentially at the corners. At the highest volume fraction considered, ϕ=20%, particles sample all the volume of the duct, with a lower concentration at the duct core. For all cases, we find that particles reside longer times at the corners than at the wall centers. In a duct with lower duct to particle size ratio h/a=9 (i.e., with larger particles), ϕ=5%, and high bulk Reynolds number Reb=550, we find a particle concentration pattern similar to that in the ducts with h/a=9 regardless of the solid volume fraction ϕ. Instead, for lower Bulk Reynolds number Reb=144, h/a=9, and ϕ=5%, a different particle distribution is observed in comparison to a dilute suspension ϕ=0.4%. Hence, the volume fraction plays a key role in defining the final distribution of particles in semidilute suspensions at low bulk Reynolds number. The presence of particles induces secondary cross-stream motions in the duct cross section, for all ϕ. The intensity of these secondary flows depends strongly on particle rotation rate, on the maximum concentration of particles in focusing positions, and on the solid volume fraction. We find that the secondary flow intensity increases with the volume fraction up to ϕ=5%. However, beyond ϕ=5% excluded-volume effects lead to a strong reduction of cross-stream velocities for Reb=550 and h/a=18. Inhibiting particles from rotatingalso results in a substantial reduction of the secondary flow intensity and in variations of the exact location of the focusing positions.

Contour plot of the crossflow velocity magnitude Vf2+Wf20 and velocity vectors around a particle: (a) the particle moves and rotates freely through the duct and (b) the particle moves downstream with spanwise angular velocity set to zero. The red circle shows the position of the particle center.

We consider an active Brownian particle moving in a disordered two-dimensional energy or motility landscape. The averaged mean-square displacement (MSD) of the particle is calculated analytically within a systematic short-time expansion. As a result, for overdamped particles, both an external random force field and disorder in the self-propulsion speed induce ballistic behavior adding to the ballistic regime of an active particle with sharp self-propulsion speed. Spatial correlations in the force and motility landscape contribute only to the cubic and higher-order powers in time for the MSD. Finally, for inertial particles two superballistic regimes are found where the scaling exponent of the MSD with time is α=3 and α=4. We confirm our theoretical predictions by computer simulations. Moreover, they are verifiable in experiments on self-propelled colloids in random environments.

3a8082e126