hi everyone,
im relatively new to houdini..
while following the Particles tutorial at SideFX site, i have come across some gliches which im frankly not able to get right.
the grouping is somehow not working as its supposed to be according to the tutorial.. (i believe there must be some changes in 9.5 and 8 versions)
i tried my way around the issue but im stuck with getting the exactly opposite set of particles inside a group..
since i need the complement of the set of particles in the group i was wondering if i can invert the grouping somehow (this is still elusive to me)
I cant really find any nodes that could do this, so i presume its gotta be done with the combine section inside the group node. (all these ops were inside the popnetwork)

i also tried deleting non selected particles but again results were what i dint want..(i couldnt delete inside the popnet so these were done at object sop level)


another issue (about which im really curious) is, somethin i saw in a tutorial by cmiVFX for building procedural cities..the tutorial is really good and gives extensive knowledge about some of the functions and expessions, however im stuck at a point where the trainer (david gary i believe) stamps the Group Name section to call in a loop.
when i did the same its showing a yellow flag error saying “Invalid Group”
(i also had put up backticks to declare name as an expression)
but its not working..
i felt propbably the same could be achieved using the FOREACH loop but im unable to think of a way to proceed with it as im new to Houdini.

could anyone help me out with these issues
cheers

If you want the inverse of an existing group, go to the Combine folder of the Group sop and create a boolean operation.
Your inverse group needs a name, so put that in the left hand field, then click on the “not equal” symbol and in the right field you can select your existing group name.

Regarding your invalid group, I'm can't remember what that lesson is calling for but is your group points or primitives? And is that the correct type of geometry being asked for?

hey probbins..thanks for the reply..
grouping thing i'll check out right away..

regarding the error ‘invalid group’ on the group node's name field im posting the screen capture of the workflow..

as shown in the pic i have traced an image to get a mesh out of it..
im working on a selected primitive so i deleted the others with the delete nodes..

delete1 is the node where im trying to stamp in the group's name field..
in the delete1's group field i have put in the following expression

'stamp(“../copy1”,“xyz”,36)'

i have tried it even without the backticks but it shows a yellow error flag sayin “invalid group”


Basically i wanted to apply some changes (extrudes etc) on only one primitive face and then apply the same to the rest of them using the copy node and its stamp function. (as shown in the tutorial by cmiVFX Procedural cities)

but i cant really figure it out yet..

Hi,

It's best to post your hip file so we can all take a look and see what's going on.

Cheers!
steven

hey thanks steve..it'll be up by tommrw positively..

hey guys this is the hip file for the setup..
hope to see some help now
thanks a lot

you should probably type the stamp expression in the “pattern” field of the offending delete sop. Also, yes the foreach sop would be the more direct approach for which this used to be the workaround

hey thanks tallkien..
i did as a matter of fact try using it in Pattern field but then it deletes all the primitives..which doesnt get me anywhere..

as im new to houdini, i cant actually tthink of how to go about the foreach loop.. i just took a logical guess as this(foeach loop) is a bit similarr to copy stamp function..

I would appreciaqte if anyone could look into the hip file and post a modified version of it..

what i want to achieve: what i want is to delete all the primitives of generated by the trace SOP except one…apply some extrusions etc on it and then apply these same fuctions to the rest of the primitives (so that i have procedural control over the structure)

cheers

I'm a little confused, are you trying to do something similar to this?

Hi

Your expression is correct, the thing is, you are typing that in a group field, which expects a STRING,

`stamp(“../copy1”,“cy”,36)`

just add the back ticks at the start and end to EVALUATE the expression
and everything works


:shock:

thanks guys i appreciate ur help..

@ allegro .. yes i do want something similar to this BUT only to one primitive for example primitive no 36…then i want to cookie it out with the other extrudes and then apply the same action to all the other primitives using the stamp function on the delete node.. i dont know whether thats what u might have done..gonna check it n let u kno later (i dont have internet at my disposal right now so its gonna take a day )

@varomix.. i did try this with the backticks but i still have the problem (probably a bug in my version..or probably a careless mistake committed )..although i will again try this out with back ticks and post the results here…

thanks a lot for your initiatives guys
cheers

Hi

I downloaded your scene and it works here as I told you

you need to use the backticks next to the one key, in the upper left of your keyboard.

I only have apprentice, so this is so you can see it working

hey thanks a lot varomix..
gonna check itout right away..(could nt do anything since last 2days..terrorist blasts goin on here)

thanks a lot man
cheers

hey thanks guys for helping me out..
@varomix..thaks man..it works

what i was doing was putting single quotes instead of backticks..thats outright silly..
thanks a lot..
hope to learn a lot from you guys
cheers