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michael

l-system question

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has anyone had any trouble with the 'pruned growth' tutorial in the docs?

it's one I've never tried before...can't think of why I never did...but now that I have done it...it doesn't work LOL

it's VERY simple - 3 metaballs > merge1 : l-system + merge1 > merge2

the rules for the l-system 'look' OK - and they are straight from the docs, and it is within the bounds of merge1...

hit play and the l-system is supposed to grow within the bounds of the metaballs...but in my case nothing happens...?

houdini 5.5.208 + Win2000

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bah....I fixed it :|

have to pay more attention to what I'm doing....

but now that it is working, I have another question about the conditional statement : in(x,y,z) ...is there a way to grow an l-system only where there is geometry - I dont mean within, but at...like if you wanted a vine to grow up the side of a wall...I guess what if looking for is some kind of zone....

hmmmm....more brain activity needed :)

ah...I think what I'm trying to ask (funny how hard it is to ask a question when you don't know what the hell you're talking about :) )

is how to use 2 objects as a meta-test object?...

eg: one metaball inside the other and scaled down a bit....picture

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hmmm...well I found in the docs that you can't do exactly what I wanted... :(

oh well...

lets try another question...

is there a way to use variables in a rule eg: A=F//+$MYVAR

or to use and expression eg: A=F//+`eval(me)`

?

does anyone use l-systems? :unsure:

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i've tryed using l-system for my trees and they can out quit well. the only thing is it's the hardest thing in the world to fined out anything about how you creat things. you can find thousands of information about the rules but no examples of rules or examples with the rules.

good luck bren

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does anyone use l-systems?  

asked myself this one a million times!!!

yes, people do, and I know exaclty how you feel about what you're doing...I been trying it on and off for the past few moths, and in short, trust the metaball pruning method for simple constraints. if you want to get more sophisticated, you can increment variables inside your L-system rules, and then disable or enable rules based on it, problem is, it doesn't take into account "world" constraints (as in: crawl that wall, go round that column) you'd have to do that with good ol' SOPS (creep SOP)...hmm...

hope I didnt' confuse you yet...wish I had time to tell you more or post an example...more to come when I find the time...it can be really rewarding...

and cs00Bren....the best way to find examples with the rules is the "Algorithmic beauty of plans book"...or the siggraph papaers from the same author....I can't remember anywhere else where you could find such examples...but they do a good job at pointing you in the right way...

cheers...

and please...keep using it, that makes at least 3 of us that are interested ;) (on this forum at least)....

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thanks sirogi...

I think I 'get it' about 60%...I think I'm often trying to do things that defeat the whole point of l-systems....but it would be very cool - and achieve what I'd like to try to do - if it was possible to have an " at(x,y,z) " as well as the " in(x,y,z) "....'creep' you say? hmmmm...

you can increment variables inside your L-system rules, and then disable or enable rules based on it

is this info in the docs?...I'd love to know how to do this...I'd like to be able to, if not control, at least 'influence' the groth of an l-system based on other factors in the scene...

thanks for the encouragement :)

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is this info in the docs?...I'd love to know how to do this... 'influence' the groth of an l-system based on other factors in the scene...

absolutely, (the onlihe help in the SOP) if you look at the construct:

[lc<]pred[>rc]:cond=blahblahblah...

the ":cond" part is where you plug in the controlling params....

for instance

premise : A(0)

A(i):i&lt;5=FA(i+1)
A(i)=+60FA(i+1)

would execute the first rule 4 times, and switch to the second one after that.

always remember the L-systems read the rules top to bottom and use the first rule that is valid, so you can have a host of rules that are all A, the L sys will go through them one by one and only apply the first valid one...

and the first 2 variables can have a special meaning for the length and thickness say so A(k,l,m) the variables (k) and (l) are multipliers for the length and thickness (uh...check the docs for this maybe the PDF, haven't used L-sys in a while...)

don't forget to use the "b,c,d" user vars in the "Values" tab, they allow you to control features for the whole system . For instance, in the preceding example replace i<5 by i<c set the generations to something higher than 5 and play with the c slider, the system should change immediately....it's a way to affect the whole look of a system from one variable...

Most of the stuff here is a direct derivation from thew book, I just had to adapt the syntax a little bit, but the book is full of insights like these...

hope it made sense...now go forth and go nuts!

Cheers!!

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cool...thanks very much...

I've had a hard time finding the book....but I JUST realized that I might find it at my local University...Prusinkiewicz is a Prof there!!...LOL

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I've got the algorithmic beauty of plants out at uni a couple of months back and if you look at the pictures of the trees they have in it you will be inspiared.

cheers sirogi for the information on the rules about the first rule 4 times, and switch to the second one after that. i finally think i know how to do good trees have one rule for the trunk and a second for the upper branches

i will have to go away and spend spend more weeks tweaking my trees.

heres a picture of the bottom of my tree when i have a spare 3 hours i will render a better picture.

post-19-1044119810.jpg

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very cool!! thanks for sharing that picture cs00bren!!

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cool cool cool....cs00bren

I searched around the net for l-system stuff and came across a python script for making l-systems...one of the included files was a bunch of l-systems from the book and some others...haven't had time to play with any of it yet (I'm up to my ass in After Effects shenanigans at the moment :( ) but I'll be able to post a little test of what I'm doing tomorrow.

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my pleasure...

of course this mean you have to show us all something cool that you did with the info :P

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cheers arctor.

i looked at the sites there isn't that much new stuff there but the l-system creating program is quite useful if only they had one that was 3D!?!??!

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yeah, not much new stuff but good background and it's cool to see what people are doing.... :)

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here is a little test I did this week...

it just an l-system preset with a creep on a twisted and scaled sphere...

twist

now I'm trying to figure out how to use groups within the l-system...

what I'd like to do is put each branch into a group and then copy another l-system on to each group - so that the branches are not effected by the creep - have to dig into the docs more...getting a bit confusing <_<

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real col effect i don';t know what i would use it fore but i will use it.

have you tryed making a l-system witht he creep then using a copy sop copying another L-system on to that. the way that you could copy on to the end of the branch is create a 1k polygon with one point then use that as a leave and copy on to that group or something similar.

it's any interesting idea your's anyway as it would be so easy to reate a vine plant up a house.

bren

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the problem is that I haven't figured out groups in L-systems yet...

see the above post....

as for where I'd use it...well...I got two words for ya : "Swamp" and "Thing".

I don't know why no one has tried it before...the first time I ever saw PaintFX I thought "oooo...swampthing...ooooo" but frankly pFX are a paing in the ass....although Maya 5 will have the ability to treat them as regular geometry (mental ray anyone B) )....so there is hope for it yet....

this is why I've been riding two horses.....l-systems and character rigging.....

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