This is a quick little demo and explanation of a setup I created for doing a particle aura. Particles are emitted based on the object’s normal direction from the camera.
This is a screenshot of the VOP network that is doing the magic. Camera position is imported (into the particles’ object space). Normalized vectors are determined from each object point to the camera. Then the dot product of the object normals and direction vector are taken. If the dot product == 0, then the normals are perpendicular to the camera. Otherwise they are pointing at the camera. The range varies between -1 and 1, which is then made useful for remapping by taking the absolute value and reversing the grad values so the user interface makes a little more sense.
The “emit” point attribute is promoted to a prim attribute after the vop, allowing it to be used as a particle birth attribute.
Technical Repository 
Brilliant.
If you combined this function with an Iso Offset and meshed your object and the particles you could end up with a very nice effect !
That’s actually what I ended up doing for the original project this setup was used in. Had to create an aura of fire around a character. Hopefully I can post the results at the end of the year.
Hey man, check out this Houdini tool I created. Still a little rough, but I figured if anyone needed to make buildings you could blow up with interiors and stuff ala 2012… heres a way.
Matt,
Your tool looks pretty sweet! We should exchange some setups at some point.
I’m currently exploring l-systems. Hoping to post some experiments here in the next few weeks.
could we see the hip file? that pretty interesting , i’am new to houdini that would be helpful
Check out the image attached to the post. That basically gives you all the info for doing the setup.