cmivfx procedural modeling issue

[mihai architect]

Hi guys ! Today I started venturing into the cmivfx procedural modeling video. For those who don't know it, is the one with the tank modeling process. So I started modeling the caterpilars as indicated by the instructor. But then I found, that at some point when he creeps an "array" of boxes ( I mean the loop/belt that surrounds the wheels) he uses the creep SOP whitch is good but the distribution of the boxes across the surface is not OK at all. So I tought of a different way to do it proper but now I encounter another issue that I cannot solve. I get a peak in the apex of the caterpillar making the curve not smooth and this ruins the chain of the network when creep-ing. I attached a file. You should figure the problem from there. Thank you !

tank.hip

[mihai architect]

meanwhile I found a way of solving the issue tough I'm not satisfied because I ran into another problem. When creeping some boxes for example on a looping geometry such as a tube, a belt, etc the first and last boxes doesn't have that even space in between like the rest. I know is because of the calculation of the creep and this is the way it works, but how can I fix this issue.

[mihai architect]

here is an image of the problem

[petz]

i don

tank_1.hip

[peterr]

Here's another approach using the Align sop. It avoids the problem of the tracks distorting caused by the creep.

tank_PR.hip

[mihai architect]

Very cool examples ! Many thanks ! I learned a lot from your setups .What I was interested, was that the caterpillars should roll. When I posted the problem with the creep union on first and last metal parts I was trying to keep a way to roll the thing on the ground. Thats why I was trying a solution using the creep. Petz 's variation with a creep solves the problem of the stiching parts but the roll now doesn't function. Here I attach a file with the same creeping problem ( I know it's not a very big deal, because when moving the problem can hardly be seen, but I want make it right) at least it can be animated. The file has contains animation of the terrain and roll of the caterpillars on it. If anyone could help please !

ps: Petz could you please explain what $TX2, $TY2, $TZ2 does more exactly. Does it take the circle and matches to x y z coordinates of the second input? That's where the "2" comes from? I don't really understand. Another thing is the knotslide on that Basis SOP, what does it do in this case? It lenghtens the spacing between the U's so that the first and last parts of the caterpillars won't stich? I don't quite get this either. And why the creep pivot now does not continuous roll anymore. Is it because of the Basis SOP that break the network?

tank_1.hipnc

[mihai architect]

or maybe is there anyway to keep your setups whitch all are good, but for the animation of the caterpillar roll to animate the points on the path, changing/animating their order so the parts sould follow the new points (but in this case the roll could not be seen, and it is steppy / blocky. The best way would be to animate the roll of the points on the path curve but I don't know how. I say this in the case that creep variation would not work finally. Meanwhile I will keep it like you see it in the attachment, but with the small creep problem, while trying to solve it otherway.

[Marc]

I don't have a Houdini available, but have you tried using a primitive SOP to open (or unroll?) the tube? Or was that only on curves? hmm... . Perhaps a carve SOP would fix the problem?

I'm talking about the image up there, so if you've sorted that particular issue then ignore me .

M

[mihai architect]

Hi Marc ! The purpouse here was that besides the creep union prpblem seen in the image the hole parts should roatate like a catterpillar of a tank. The carve SOP as far as I know breakes the continuous path of a curve or tube ar whatever surface that is a belt. I'm tryin to solve both the issue in the image and the roll one.

[petz]

"ps: Petz could you please explain what $TX2, $TY2, $TZ2 does more exactly"

$TX2, $TY2 and $TZ2 in the point sop are fetching the xyz position of the second imput.

"Another thing is the knotslide on that Basis SOP, what does it do in this case?"

by using the knotslide you can slide the boundary where the two ends of the surface fits to each other or just create a gap in the surface parameterization.

file with rolling catapillar is attached!

petz

tank_2.hipnc

[mihai architect]

wow ...I'm stunned...I just looked at your file Petz and on the first look I can barely understand something right now...but it's really WORKING.That's all that matters. I guess I'm too tired right now, so tomorrow I will digg and try to find out the use of all those expressions and how you put it all together. Hope I can track it down and understand the solution/s you made. Thank you very much Petz for your time. Hope I won't bother you again with my questions. Many thanks !

[mihai architect]

Hi Petz ! I looked over your file and I can say that all your variations are very cool (the most elegant avoidance of the creep issue is the second one, with the box copied over the points of a line except the last one...very clever...I didn't tought of that) and I like the third with the fuse applied after the creep sop. But the reason for my reply is that I don't understand the behaviour of the Point SOP on variation 1. I could see that the normal of the Facet SOP before are facing perpendicular to the caterpillar plane. But when Point SOP comes in, the whole thing changes. The normals I mean. I don't understand why and the expression of the Add Normal "$TX-point(opinputpath(".", 0), $PT - 1, "P", 0)". So please explain me this expression. I understand the expression of the Add Vector, because I searched all the documentation. But I don't understand how the data is processed through the Point SOP and in whitch order. One last thing: the string attributes like P, or Pw, or N are a standard to use, like pre-made? So when I use "N" I'm refering to the normals? Are there other attributes like such P, Pw, N ? Because I didn't found any mention of those in the documentation. If there are I would like to know them at least. Thank you very much !

[petz]

"I don't understand why and the expression of the Add Normal "$TX-point(opinputpath(".", 0), $PT - 1, "P", 0)". So please explain me this expression."

its nothing fancy. the expression recalculates the normals by using vector subtraction.

for instance take a look at point 10. $TX is a local variable and means the position of the respective point, in this case point 10. $PT - 1 in the expression returns the point-number - 1. accordingly point(opinputpath(".", 0), $PT - 1, "P", 0) returns the position of point 9. so it

[mihai architect]

Thank you !

[peterr]

Here's another alternative for getting your tracks to roll.

creep_line_rotation.hip

[Nerox]

Very cool examples ! Many thanks ! I learned a lot from your setups .What I was interested, was that the caterpillars should roll. When I posted the problem with the creep union on first and last metal parts I was trying to keep a way to roll the thing on the ground. Thats why I was trying a solution using the creep. Petz 's variation with a creep solves the problem of the stiching parts but the roll now doesn't function. Here I attach a file with the same creeping problem ( I know it's not a very big deal, because when moving the problem can hardly be seen, but I want make it right) at least it can be animated. The file has contains animation of the terrain and roll of the caterpillars on it. If anyone could help please !

ps: Petz could you please explain what $TX2, $TY2, $TZ2 does more exactly. Does it take the circle and matches to x y z coordinates of the second input? That's where the "2" comes from? I don't really understand. Another thing is the knotslide on that Basis SOP, what does it do in this case? It lenghtens the spacing between the U's so that the first and last parts of the caterpillars won't stich? I don't quite get this either. And why the creep pivot now does not continuous roll anymore. Is it because of the Basis SOP that break the network?

This is a little off topic, but I'm stuggeling with the creep SOP like you use in your original setup. I get a lot of fancy shapes, but nothing close to what one would expect.

In my case I'm trying to 'map' a grid with some extrusions to a circle. The idea is to model a flat profile of a tire and defrom it some how to make it round. Great thing about using a curve as a base is one's able to deform the final result based on a curve.

Strange thing is, if I copy/paste the grid/tire part in your scene, with some scaling modifications on the creep SOP, I'm able to project the profile on your curve.

I've attached a scene file

Tire01.hipnc