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..::sun 1/2::..

Note from the author: This article was written with 3ds max 5 in mind. It should be noted that later versions of 3ds max contain an advanced particle system which can be used to create a more effective result, and a shedload easier!

Believe it or not, this is a biggie. Actually, it’s pretty much the largest Q&A I’ve come across so far, so much so there isn’t enough space to cover everything this month (paper), so we’re going to have to split it into two sections – the Flare particle motion this month and the rest (the materials – sun’s animated surface, flare texture, and other effects) next month (paper).

Okay, why is it such a mammoth task? Isn’t it just a big white blob in the sky? Well, yes. And no. It all depends on how you see it; actually what you see through to see it. The majority of all solar footage available to us (thanks to NASA’s huge library) shows the sun using UV photography. This is mainly due to the huge amount of light emitted from the sun making it nigh impossible to capture an image of it by any conventional means.

This therefore means that any animation or image is based on an artist’s interpretation of what the sun looks like through a UV camera. In reality you wouldn’t be able to see anything with a normal camera as all you would get is a full frame of white and a very bad tan. Therefore any reference material we have is based on UV photography as this makes the sun’s surface visible to us in an aesthetically pleasing way.

Typically, solar flares (which, again, are normally only visible using UV photography or during a solar eclipse) shoot out for millions of miles, but due to the gravitational forces of the sun, they curve back round and come back into contact with the sun, forming a large arc. However, some times solar flares have enough energy to escape the gravitational attraction of the sun and shoot out into space which tend to look more like masses of ejected fluid. Therefore we will have to try to incorporate both of these into our cg simulation.

To create this effect we will have to use multiple particle systems. The first system is designed to be a simple emitter, creating the gravitational curve. This system is emitted initially from a low poly clone of the renderable Sun Geosphere that has an animated sub-object selection on it generated by an animated noise map used within a Volume Select modifier. Using maps this way to generate the sub-object selection gives us more control when designing the selection as opposed to a static vertex / polygon selection or using a selection generated by intersecting objects which would take more time for the software to calculate. As only a few polygons are selected in the Geosphere emitter, the emitter particles appear randomly over the surface, and as the selection is animated these particles do not appear from the same points every time. The curve motion is created using the initial velocity of the particle(s) and a gravity Space Warp which pulls the particles back down to the surface.

As we cannot use particles to emit particles with the standard system, we have to use a Mesher object in which we create a copy of the particle that the Trails system can use as an emitter, dropping particles as the emitter system moves, thus creating the gravitational curve. As these particles are not affected by the gravity warp they remain static, therefore to make them float out into space we can add a low intensity Wind Space Warp to control this motion.

The resulting effect is quite convincing, but looks too wispy, and almost like cigarette smoke. So we can duplicate the particle systems and Mesher object (ensuring that each object references the correct emitter – eg Mesher02 is used on the Emitter02 system and Trails02 is emitted from Mesher02) and by amending the speed of the emitter particles slightly, we can create a “ring” effect – similar to a planetary ring setup, that will be slightly visible until the wind Space Warp kicks in and disperses the particles out into space, creating our desired look. An alternative method would be to use one emitter, mesher and trails system, but to use a long thing plane as instanced geometry for our emitter particle’s particle type, with the trails system set to emit from vertex positions.

As 3ds max subscription users now have access to Particle Flow, they should be able to translate the steps used to create this effect using the standard particle system, using this new system to add additional control and effects.

That’s it for this part. Check out the next paper where we’ll be finishing off the scene with animated materials and additional effects.

Enlarge Screenshot Open sun_flare_start.max . Add a Noise modifier to the non-renderable “sun mini eruption generator” Geosphere. Set the Noise scale to 10, turn on Fractal and set the X Y and Z strength to 5. Add a UVW Mapping modifier and set to XYZ to UVW. Add a Volume Select modifier, set to Face selection level and Select By Texture Map.
Enlarge Screenshot Click on the “None” button underneath the Texture Map selection icon and add a Noise map. Instance copy this map to a slot in the Material Editor and label it Face Selector. Set the Size to 1, High to 0.5 and Low to 0.2 . Animate the Phase from 0 to 100 over the 500 frames. Create a Gravity Space Warp and position it in the centre of the Geospheres.
Enlarge Screenshot Create an SDeflector Space Warp with at radius of 199 and centre it as before.. Set all other settings in the Space Warp to 0. Create a Wind Space Warp, label it “Wind Emitter” and reposition it at the centre of the Geospheres as before. Set the Strength to 0, Spherical Force and Turbulence to 0.5. Clone the Wind and label it “Wind Trails”. Set the Strength to 0.2, Turbulence to 0.05 and Scale to 0.015.
Enlarge Screenshot Create a PArray particle system and label it “PArray emitter01”. Choose the “sun mini eruption generator” as the emitter. Turn on Use Selected Sub-Objects, set the Percentage of Particles to 100, Use Rate to 1, Speed to 20, Speed Variation to 50, Divergence to 90, Emit Stop and Display Until to 1000, Life to 50, and Grow For and Fade For to 0. Bind the Gravity, SDeflector and “Wind Emitter” Space Warps to the particle system
Enlarge Screenshot Create a Mesher Compound Object using the particle system and align the two together if necessary. Label it “Mesher Emitter01”. Create a PArray system and label it “PArray Trail01”. Set the Mesher Emitter01 as the emitter, Use Rate to 100, Speed to 0 Emit Stop and Display Until to 1000, Life to 100, Life Variation to 20, Size to 2, Size Variation to 10, Grow For to 0 and Fade For to 50. Set particle type to Standard Facing and rotation spin time to 500. Set Object Motion Inheritance Influence to 0.
Enlarge Screenshot Bind the Wind Trails Space Warp to the new PArray system. Clone the PArray Emitter01, Mesher Emitter01 and PArray Trail01 items another 9 times. In each copy of the Mesher Emitter object and Trail system, make sure they refer to the correct items (eg 02 to 02, 05 to 05 and so on). Space out the trails particles by slightly amending the speed of their respective Emitter particles as illustrated. (Continued in the Tips section...)
Enlarge Screenshot The particle systems in action. Okay, it may look like a lot of overkill, but the result is effective and the render times not all that high.
Download the max file! Zip file to accompany.

..::tips::..

Hide the Emitter systems and Mesher objects and add copious amounts of Image Motion Blur. Settings around of 3 assigned to the Trails systems should be enough to smear the particles, blending them together and creating a nice flare effect and also reducing the amount of individual particles visible in the scene.

An additional PArray system has been created to create short flares from the surface of the sun. This system uses the same emitter as the flare emitter particle system(s), but with a limitation on emitted points (At Distinct Points selected in the Particle Formation section). A low speed and lifespan creates the small puffs of fire and the speed variation ensures that the system does not look too uniform. Again, facing particles are used.

Due to the amount of particle systems and the sheer number of particles flying around in this scene, your machine may have a hard time while working in the Viewport. In which case, reduce the amount of visible particles in the Viewport so you only view those that are necessary to the part you are working on.

In the same way as the Viewport may have a hard time calculating the amount of particles in the scene, so may the renderer. In fact, if your system hasn’t got that much memory inside, you may well encounter several “Out of Memory” errors when the renderer is trying to calculate the particle systems. In which case, remove a few of the systems and/or reduce the Use Rate in the trails particle systems.

Initially published: 3D World magazine, Issue 42, September 2003.

Copyright Pete Draper, September 2003. Reproduction without permission prohibited.

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