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The above illustration shows a particle that happens to have the same size of as the cell. But even in this case, it isn't certain that this cell will show any density , if the density multiplier and final density Density Multiplier and Final Density settings are too small, because the cell still has a certain distance to search before finding this particle. The longer this search distance is, the more faded the density becomes.
Lets see some more examples:
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Here the cell size was increased to 2cm. Since the distance each cell has to search has increased, nothing appears in the render. We could raise the Radius Multiplier in this case to make the particles bigger, or lower the cell size again to make some density reappear. In We could in fact we could also raise the cell size even more, and some density would appear again. See the next illustration for why this happens.
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Now the cell size is 3cm and we start seeing some density again. This can seem very unintuitive at first, but looking at the grid of cells, it is clear that now some corners of some cells are actually closer to a particle compared to when the grid was set to 2cm. So we start seeing a very rough, square representation of these particles, because the cell size is so large.
Density multiplier as a "falloff"
All renders with a cell size of 2mm,
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Max Final Density at 500. Only the Density Multiplier changed: 10000, 3000, 1000.
This series of images is ment to show two things. First, that with a small enough cell size, each particle can be very well defined (in these renders the cell size was reduced to 2mm (a setting of 0.002). Second, and secondly, how the Density Multiplier parameter can act as a sort of falloff between areas of density and no density. The Max Final Density was 500 for all renders. You can see that as the Density Multiplier decreases, there is a larger area of falloff between no density to the areas of maximum density. When the Density Multiplier is very high, there is a very sharp falloff, making the volumetric shape have much sharper contours.
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