# Performance: Many Overlapping Surfaces/Polysurfaces

**URL:** <https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456>\
**Category:** Rhino for Windows\
**Tags:** windows, performance, surface, groups\
**Created:** [March 15, 2021, 8:37pm UTC](https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456 "2021-03-15T20:37:46Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![jfreund](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/jfreund/32/288054_2.png) [@jfreund](https://discourse.mcneel.com/u/jfreund)\
**Post date:** [March 15, 2021, 8:37pm UTC](https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456/1 "2021-03-15T20:37:46Z")

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Here is a previous Forum post, with a recommendation from ‘jesterKing’:

> [@Texturing multiple overlapping surfaces or using decals help](https://discourse.mcneel.com/t/texturing-multiple-overlapping-surfaces-or-using-decals-help/40188/2):
>
> Don’t create overlapping surfaces that are exactly in the same plane. Select your geometry with holes and translate on the z-axis by the tiniest amount, 0.0001 might already work, maybe even 0.00001. Another option is to create you parts in such a way that you don’t get overlapping surfaces in the same plane.

Are there **performance** reasons why a user may want to avoid overlapping surfaces on the same plane (both for modeling and rendering)?

What if both surfaces have the same material?

I have a model with a facade that is causing performance issues. It has been modeled with groups and blocks which have been arrayed such that there there are hundreds of duplicate surfaces / polysurfaces that are overlapping (at a column, frame, or mullion). 🙁

There is certainly a lot of redundant geometry that could be purged, but it would be very tedious and time consuming at this point. Do the overlapping surfaces/polysurface affect performance in a unique way?

Thank you,  
JF

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**Author:** ![pascal](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/pascal/32/479395_2.png) [@pascal](https://discourse.mcneel.com/u/pascal)\
**Post date:** [March 15, 2021, 8:44pm UTC](https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456/2 "2021-03-15T20:44:00Z")

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> [@jfreund](#):
>
> affect performance

Hello - what do you mean by ‘affect performance’? In a ghosted viewport having many overlapping objects will slow down selection. Otherwise, without transparency, I don’t _think_ there is a lot of difference in performance whether the surfaces are coincident or just near each other - but fewer objects is better than more objects…

-Pascal

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**Author:** ![jfreund](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/jfreund/32/288054_2.png) [@jfreund](https://discourse.mcneel.com/u/jfreund)\
**Post date:** [March 15, 2021, 9:14pm UTC](https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456/3 "2021-03-15T21:14:32Z")

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Hi Pascal, thank you for the prompt response!

I think you pretty much answered my question, but let me clarify:  
Are more resources required when:

A) Rendering two identical polysurfaces that are in the exact same location such that each subsurface is completely overlapping  
VS  
B) Rendering just one of those polysurfaces  
(No Ghosting)?

Both renderings would look the exact same in the end, but just wondering if A requires more resources. The model I’m working with has tens of thousands of this condition throughout model, so I’m wondering if a cleanup script is worth considering to help with performance and rendering time.

Thanks,  
JF

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**Author:** ![pascal](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/pascal/32/479395_2.png) [@pascal](https://discourse.mcneel.com/u/pascal)\
**Post date:** [March 15, 2021, 9:25pm UTC](https://discourse.mcneel.com/t/performance-many-overlapping-surfaces-polysurfaces/120456/4 "2021-03-15T21:25:49Z")

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Hi JF - in rendering, the sources needed would go up with the sheer number of surfaces - not necessarily proporitinally, but up; the amount would depend on things like transparency and reflections, I suppose - if your coincident surfaces have reflective materials, then I can imagine there is that much more to calculate as the two reflect into each other…

In any case, if you have tens of thousands of coincident or near coincident surfaces, I would say it is certainly worth culling those extras.

-Pascal