attribPromote???

[Adam Ferestad]

I am trying to use a scatter node with the ptarea turned on to generate a density function on a tile that I have put together (I made a nice hexagonal grid system). I want to use this information to place buildings on each tile, but I am having trouble getting the ptarea attribute to promote onto the primitive. It is more of a learning exercise in trying to use random distributions to control structural elements of copied geometry. Anyone have any ideas how to figure out the point density on a given prim?

[Macha]

Hey Adam, it's a little silly but how about copy stamping a tiny square (=primitive) on each point, then attribute transfer the primitive attribs to the geometry and attribute promote (sum) the attributes.

[Adam Ferestad]

hmmm... I am not sure that will do what I am trying to do. Basically, what I am trying to do is extrude a primitive based on how many points are scattered onto it. Once I have that mechanic worked out, I can do more of what I am trying to work thorough. is there any way of counting the number of points on a primitive? I have a feeling that I am simply missing an expression or something.

[edward]

It can be done, but in a very roundabout way. I hope someone can come up with a better way.

- Append AttribCreate SOP (to your grid) to create the primitive attribute named "prim" that is set to use $PR as its value. (NOTE: I'm assuming that you're scattering onto polygons)

- Append Facet SOP to compute normals on your grid

- Append Scatter (etc)

- Append Point SOP, with positions set to $TX-$NX, $TY-$NY, $TZ-$NZ (ie. offset the points in the reverse direction of the normals)

- Append Ray SOP, with the second input set to the Facet (aka the input of the scatter). Turn on "Import Attributes from Hits". Move the * from Point Attributes to Primitive Attributes. You now have for each point, the primitive number that it belongs to.

- Append Partition SOP (name it partition1), set Entity = Points, Rule = g$PRIM

- Go back to the Facet and branch out an AttribCreate. Set it to create a Primitive attribute with the value expression set to argc(pointlist("../partition1", "g" + $PR))

[petz]

here´s another way with a little help of pyhton.

hth.

petz

dens.hipnc

[Adam Ferestad]

petz, that is doing exactly what I am looking for, unfortunately I have never edited Python in Houdini, so I am having some trouble seeing what you did. How do I see the python code?

[zarti]

... . How do I see the python code?

> rightClick over the node

> Type Properties ..

> select Code tab

.cheers

[Adam Ferestad]

OK, that looks really simple and strait forward, elegantly so. now I just have to figure out how to get those numbers pushed back onto the points. I am really rough with coding in general, but I think I have a feel for what the line would look like. I am assuming that I would have to make a list of the points and pull the dens attribute from the nearest prim? Unfortunately I am still rough on the syntax for doing that. This is a great learning project though, and I think it will help me get my head around Python a bit once I get it figured out. Thanks for the help guys.