Vray Scatter

[jim_morvay]

I see that with the latest update, a lot has changed with Vray Scatter. One of those changes has really got me confused, and that's with regards to Instances Count, Per Area and Density. It seems that the larger the scatter area, the worse the distribution is, compared to the previous version where you only needed to specify one amount in order to get the results you want. I have large grassy areas I want scattered, but the problem is that whether I choose Instance Count or Per area, the larger the amount I input, the less I see, which seems counterintuitive. Of course, in classic Chaos fashion, there is limited documentation as to how this all works, from a practical standpoint.

I did a test, where I created to scatter areas, one large and one small. The small one scattered very well and the amount I specified, created a very dense grassy area. I wanted to achieve the same with the larger one, but all I get are patches of grass, no matter if I specify a large or small number for the instance count. If I switch to Per area, again, I expected to see more grass if I specified a larger number, but in fact, I see less. Lowering the number did increase the amount, but if I went too low of a number, then it became unchanged.

I'd really really love to find some good information somewhere, where the new scatter and its parameters are clearly explained so I can learn and understand how this new process works. I understand that it was refined to help prevent crashes, which I do appreciate, but at the same time, good, clear explanations of how it all works, would help me achieve what I need. For now, I am having to break up the large area into smaller ones and specify multiple scatters.

[Peter.Chaushev]

Hello, Jim
Firstly, thank you for your feedback!
When Scatter was redesigned its UI elements almost tripled. While most fine-tune controls are actually very basic I understand the overall appearance of the settings layout may look intimidating and confusing at first sight.
We'll have the online documentation gradually updated with visual examples to provide more clear explanation of each parameter. Refining some options to make them more obvious is also on the table.
Additionally, further improvements to Scatter are on the to-do list (e.g. the 'Edge Trimming' feature). All ideas to improve its usability and capabilities are under considerate attention.

For now, let me provide some details to help clarify how the new Scatter functions:

• 'Instance Count' specifies the number of instances generated on a given host before any conditions of their distribution are applied.
  Here is an example of limiting surface distribution by slop angle. Notice initially there are 20 instances but after applying a 45 degree slope limit, some of them are trimmed away.
  After applying this condition no extra instances are generated to compensate the reduced total number. This means the Instance Count value is the netry:
  

• Scatter treats multiple host objects as one with combined surface area (or volume).
  If you set Scatter to produce 100 instances of a guest object over two host objects it will not produce 100 for each host. Instead it will produce a total of 100 randomly distributed instances over the combined surface area (or volume) of both host objects.
  Here is how the previous example looks with one host object instead of two. Since there is less surface area the instance positions are recalculated and appear denser:
  

• 'Max Count (Limit)' is a limit set in place to help avoid creating too many instances and overloading your system.
  This options has no effect if your 'Instance Count' value is lower than the Max Count value. Depending on the hardware used this limit can be adjusted to ensure smooth performance and avoid excessive memory consumption.

• Using a Density map generates brand new instance distribution.
  This means the Density map does not "trim away" the original distribution in areas corresponding to black color (0 value). The total amount of instances (approximate to the 'Instance Count' value) is preserved and is distributed on all surfaces that correspond to map values above 0 (parts of the map not being purely black).
  Instances have higher probability of being generated in areas corresponding to higher values of the Density map, relative to darker ones.
  

• Scatter density = 'Instance Count' value / 'Per Area' value
  The 'Per Area' number value is used to define the size of a square area covered by the amount of instances specified in 'Instance Count'.
  Essentially, the two parameters define density as instance count per specified square area. Therefore, increasing the 'Per Area' value decreases density.
  I know it is easy to consider the label means "(Instances) Per Area". This complicated control is a result of integrating this feature in different products. Hope to make it more intuitive through further UI refinement or perhaps or even deeper tweaks.

• SketchUp works in inches under its hood.
  The cherry on top of defining a square area for Scatter density is that SketchUp always does its internal calculations in inches.
  So, regardless of the display units, the Scatter 'Per Area' number is always in inches. In the example below you can see an instance count of 5 distributed over 1m (or ≈ 39").
  This is not the only V-Ray parameter that is conformed to this logic. The V-Ray for SketchUp team recognizes this is not a good solution and it needs to be improved.
  

Hope this info helps.
Would like to stress once more that any feedback on Scatter is extremely valuable in our effort to refine its usability further!

[jim_morvay]

Thank you, Peter, for the more in-depth explanation of the new functionality. I can't say I better understand the functions from before, but it gives me a better understanding of how to go about moving forward with utilizing Scatter. I assume there is no more of the "one and done" function to Scatter, whereas it no longer has limited abilities. I've seen a video or two recently, showing how the Scatter can operate as a function to scatter objects over a surface, but with selective ability (ex. grassy areas and mulched areas can occupy one surface and Scatter can differentiate, depending on user input).

Back to my scenario, where I have multiple large surfaces that need an even distribution of grass, what would you recommend as the best solution? SHould I use a map that is all white, to get the grass to fill the area, or do the other functions have the same ability, with less steps?