How to draw the trails of particles?

[touhou...@gmail.com]

Hi, all.
I want to show the movement of particles, so I need to draw the trails of particles, but it seems that the particle system in cesium has no such API.

I see there is an update callback in particle system, but I am not sure if it can help me to draw the trails, because I can not tell which particle I am updating.

Any suggestion?
Rayman

[Omar Shehata]

What kind of application are you trying to build? 

I haven't used it myself but I think the particle system was designed mostly to create visual effects rather than simulate specific behavior. It looks like particles are created as billboards:

https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Scene/ParticleSystem.js#L494-L524

So you should theoretically be able to reach in and get that list of particles, even though it's not exposed by the public API. 

Although, you might be able to use a SampledPositionProperty and a Path to draw a path for an individual (or for all?) particles, here's an example:

https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/?src=HeadingPitchRoll.html

Entities have unique id's so that can help you identify/map individual particles in the update function:

https://cesiumjs.org/Cesium/Build/Documentation/Entity.html?classFilter=ENtity#id

I hope this helped! Feel free to follow up here. I don't see a lot of people on the forum using the particle system so I'm curious what kind of application you've found for it. 

[touhou...@gmail.com]

Thanks for your help.

I use particle system to visualize the 3D force field physics effect, mainly for the wind field. The movement of the particles are used to represent the force field.

Now I have 3D wind field data for Asia continent. I am planning to put about 50000 particles, because the area is very large. With so many particles(billboards), I wonder whether cesium will take a long time to render them.

[Omar Shehata]

So I think the particle system is optimized for this kind of use case, but I don't know of its specific benchmarks/it will vary depending on whether you're testing on a desktop, or mobile device etc. 

The good news is Cesium has definitely been used to simulate and visualize these sorts of wind fields before. Here's one I found from a quick google search:

https://github.com/kobeCan/cesium-wind

I can see that they're using geometry/primitives in order to get the maximum performance. So I would try with particles, and if you're experiencing a slow down, you might try using the primitives directly. This is a good guide on that:

https://cesiumjs.org/tutorials/Geometry-and-Appearances/

[touhou...@gmail.com]

Thanks for your detailed suggestion!
I will give it a try.

在 2019年1月3日星期四 UTC+8下午11:36:43，Omar Shehata写道：

[Omar Shehata]

Awesome! If you get any cool results it'd be cool to see a gif or a demo! I also found out we have a whole meterology section in our demos:

https://cesiumjs.org/demos/Meteorology/

Which might be cool to add to.

[touhou...@gmail.com]

Hi, Omar

After two month's work, I finally make a particle system with custom render.

It is not good looking but at least it works. I attached a screenshot of my rough demo. And I made a Github repo: https://github.com/RaymanNg/3D-Wind-Field

Last but not least, thank you Omar! You help me a lot:
https://groups.google.com/forum/#!topic/cesium-dev/vR7H4KJURJ8
https://groups.google.com/forum/#!topic/cesium-dev/7kCcITmGbEA
https://groups.google.com/forum/#!topic/cesium-dev/gpgLjYyNFKE

[Omar Shehata]

This is awesome! I'm glad you resolved all the issues and have it running, and thanks for posting your code. I imagine it wouldn't be that hard at this point to add color over time like this wind map (https://blog.mapbox.com/how-i-built-a-wind-map-with-webgl-b63022b5537f), or it based on strength/speed? Then it will look absolutely beautiful!