Hello everyone
I'm learning Houdini, I have some questions about the manipulation of the center or pivot.?
I understand that we can deplace the pivot with the insert button, but how can I freeze or match with the parent pivot easily?
I have a small scene to share and I have additional questions about it. It would be nice of there is a volunteer to answer me some questions.
If this is against the forum rule I do apologize, and I will understand.
Best greetings

Have a look at this file. Try to minimize your use of transforms at object levels, for the work you are doing it does more harm than good (there was some thread somewhere on this forum that explains why transforms at obj level are bad practice when modeling). If you want to align geometry reference it with an expression or with an objectmerge (you see both examples in my file). The green color nodes are your modified geometries.

Thank you a lot for the help, I will take a look at your file and post something later on.
A thousand thank

Your file is good study case, I'm discovering lot of things I did not know about them in Houdini, amazing, but I still very interested about those few small expressions you put there:
1-in the center-base object,in the second transform node there is an expression on the X Y Z translate values that have been replaced by -$CEX -$CEY -$CEZ, what CE refers to, why it is negative, and what the reason for that?
2-in the Ibeam_base1, at the very last transform node, you are putting two expressions in the X and Z of translate, again, why it is negative and what is CENTER_BASE, is it a position expression between this object and the center_base?
I will keep studying your file, it would be nice to understand those small issues.
Thank you very much, I hope I'm not asking too much.
Greetings

Hey
I have another question:
I used in my sent file the triangle to copy the Ibeam to each vertex of it. I failed to do something clean and precise.
Isn't there a hint to make the Ibeam be copied to form a triangle of three beams in a very mathematical or practical way?
ops:

1-in the center-base object,in the second transform node there is an expression on the X Y Z translate values that have been replaced by -$CEX -$CEY -$CEZ, what CE refers to, why it is negative, and what the reason for that?

The circle will have it's center point at 0,0,0 but the triangle has it's centroid at a different coordinate. If you right click on the circle SOP you can see the size center(centroid) and bounding box of your object. I used the $CEX etc. to shift the centroid of the triangle back to 0,0,0 as you can see when you right click on the xform_Position_Center node.

2-in the Ibeam_base1, at the very last transform node, you are putting two expressions in the X and Z of translate, again, why it is negative and what is CENTER_BASE, is it a position expression between this object and the center_base?

I “referenced” the centerbase-geometry in this expression so that the center of the i-beams is at the same point as the center of the base (sort of, not really happy with the result but it was a quick way to point you in the, hopefully, right direction). Have a play with the + and - and see what it does yourself. The CENTER_BASE is the name of the null SOP in the center_base geometry. The null SOP doesn't do a thing and that's very usefull I can now reference the center_base anywhere in the network and still add new nodes to the center_base geometry itself just as long as i make these nodes before the CENTER_BASE node. To say it more simple: it's just a place holder of your geometry.

You should have a look at the introductory videos from Sidefx and Digital Tutors. They explain things much better btw.

See the attached file for a nicer way to copy the beams.


Cheers,
Hans

Hans man :shock:

Thank you very much, actually I have the digital tutors introduction to Houdini, and I'm quite sure that they did not give this subject enough time, are you talking about that mouse tutorial?
Anyhow, the last solution you gave was something I was searching for, and I think I tried to do it but manually without that Einstein expression you wrote, of course I promise to study this expression and try to adapt it to another case.
I'm joining the first stage of my oil digger, basic modelling, please feel free to comment and/or correct any common mistakes, any suggestions will be more than welcomed, my next stage will be rigging this simple model, ofcourse the model still misses the back pump.
Please feel free to take your time, I think you already gave me so much hints.
This is my second day using Houdini, and I really find this software very special in its architecture; Surely it is not click and play; It is a challenge in every small step of anything….Love it
I wish I can buy you a drink or two, please if you pass by Paris, let me know.
Best greetings and Bon weekend

I'll do anything to get a drink in Paris so here some more explanations:

The idea of the expression is to get the centerpoint of the triangle. This centerpoint is used as origin of rotation. The edges of the triangle are, in this case, all equal which makes it rather easy to calculate the center.

The center lies on the crossing of the lines which cuts the angles of the sides of the triangle in half (you still following me?)…oh what the hack, here some useful links:

http://www.jimloy.com/geometry/centers.htm [jimloy.com]
http://en.wikipedia.org/wiki/Triangle [en.wikipedia.org]

Checked your latest model and you are still using transformation at Object level. This can make your modeling process more difficult later on. It's better to use a transform SOP in the different geometry nodes and reference the other nodes. Have a look at the bbox expression (what you want is to transform in the y-direction so use bbox(“../../path_to_node”, D_YMAX) ). In the geometry SOPs, at a null SOP at the end of the chain. Name it like the geometry node and reference it in the other networks. Have a look again at the file i send you.

Now maybe sounds all discouraging but you are doing fine after using two days of houdini. Keep up the work!

Hi Hans
What is the best hint to align objects?
If I understood well, it is better to avoid playing with tansform values in Scene mode and it is better to make it in the SOP level, I was trying to to play with the align mode “not the surface align thingy” and if I'm getting to work better as it is very tricky to manipulate, I can see that the new values of the align operation are printed in the scene mode, I know then I have to export them down to SOP, but this is can be very annoying without using expressions;
Thanx for every one who can share ideas about this.
Best greetings