# TouchDesigner | Email | Volumetric Lights

Hello Matthew,
Ive been following your videos about TouchDesigner, great work! Really appreciate the content and learning resources you’ve made.

We are experimenting with TouchDesigner, so that we could perhaps use it in our dynamic / interactive installations.

Recently I have been researching usage of TD with dmx/artnet lighting and have come to a certain problem, which I just cannot solve easily. Ive been looking all over the internet, read two books about TD and still cannot figure this out. So I wanted to get in touch withou you and perhaps aks for advice (if you have time of course π )

Let me introduce the problem:

Imagine you have a 3D lighting sculpture, where there are DMX light sources all over a certain 3D space.

The lights are not uniformly spaced relatively to each other (no cubic shape or something light that), they are randomly placed in the space.

Now, I want to take a certain shape (for example a sphere) and map it as an lighting effect to the lighting fixtures. The sphere would for example had its radius increased / decreased in time, and the application should “map” which light source should light up when the sphere “crosses” it in space.

I would then somehow sample the color of the points and use that information and feed it to a DMX chop after some other operations…

It’s kinda difficult to explain, but hopefully I got it right.. π

Do you know of any tricks or components I could use, so that I could “blend” 3d geometry with points in space in order to control lighting?

Im certainly able to work out how DMX works and all the other stuff, I just dont know how to achieve the effect in 3D.

(In 2D, it would be really simple. For example for a LED screen, its pretty straightforward, I would just draw a circle or whatever on a TOP and then sample it..)

Thanks a lot,
I would appreciate any tips or advice, really.. π

Best regards,

Great question!

A sphere is a pretty easy place to start, and there are a few ways we can tackle this.

The big picture idea is to sort out how you can compute the distance from your grid points to the center of your sphere. By combining this with the diameter of your sphere we can then determine if a point is inside or outside of that object.

We could do this in SOP space and use a group SOP – this is the most straightforward to visualize, but also the least efficient – the grouping and transformation operations on SOPs are pretty expensive, and while this is a cool technique, you bottle-neck pretty quickly with this approach.

To do this in CHOPs what we need is to first compute the difference between our grid points and our sphere – we can do this with a math CHOP set to subtract. From there we’ll use another math CHOP to compute the length of our vector. In essence, this tells us how far away any given point is from the center of our sphere. From here we have few options – we might use a delete CHOP to remove samples that our outside of our diameter, or we might use a logic CHOP to tell us if we’re inside or outside of our sphere.

From there we should be able to pretty quickly see results.

Attached set of examples made in 099.

• base_SOPs – this illustrates how this works in SOP space using groups
• base_concept – here you can see how the idea works out with just a flat regular distribution of points. It’s easier to really pull apart the mechanics of this idea starting with a regular distribution first as it’s much easier to debug.
• base_volume – the same ideas but applied to a 3D volume.
• base_random – here you can see this process applied to a sudo random distribution of points. This is almost the same network as we looked at in base_concept, with a few adjustments to compensate for the different point density.

base_dist_test