Hi all,
I'm just trying some stuff out with particles - trying to get them to be attracted towards a surface. I've got that part working, but I wanted to adjust the gradient produced with a wrangle node or ramp or something.
However, I cannot seem to find a way to do this. I can't find the gradient as an attribute anywhere…I'm guessing that volume stuff is a little bit different to regular geometry
Any help would be great.

Do you gradient field modifications in SOPs. Otherwise you can attach it as a sop vector field to an empty object and run a Gas Field VOP on it though a Multiple Solver…. So do it in SOPs Then you can just read it instead of copying the data over, I would use POP Advect in this case.

I have no idea what you just said - I've not got as far as using Gas Field VOPs yet here comes the questions, but I wanted to thank you for replying.

So using a sopvectorfield to drive a field force is a bad idea? Doesn't it essentially do the same thing as an advect? Or odes the advect just move particles along field lines and the force merely pushes in that direction?

The thing I'm mainly confused about is what the name node is doing. You need to have an attribute called ‘name’ and set groups 0,1,2 to grad.x, grad.y and grad.z…why is this and how does this relate to the popadvectbyvolume node?

It's not a bad idea, it's just that the Advect node is an all-in-one and the Field Force is a lot more complicated to set up. For this particular instance they pretty much do the same thing.

I used the Name SOP to add a the primitive string attribute that the Advect POP is looking for.
'name' is a reserved attribute that identifies volumes, you can see that grad.* now shows up when you middle mouse on the node. On the Advect node it looks for the vector volumes named grad, as shown in the Field Name parameter.

“I used the Name SOP to add a the primitive string attribute that the Advect POP is looking for.
'name' is a reserved attribute that identifies volumes…”

Interesting…where did you find this out? Just experience, or is there some masterful set of tutorials I've been missing?
Some things it seems almost impossible to figure out for yourself