After working through the tutorial guide, every video, and a slew of other tutorials I have found, I set out to make something on my own last night. It was going great until I reloaded the file when I got up this morning.

It's a dinosaur. I started from a polygon cube. I had most of the torso laid out, but when I opened it this morning it was just a pile of polygons. My SOP network is intact, but when I go back through it, alot of the SOPs are evaluating incorrectly. It's a chain of polysplits, polyextrudes and edits. It all goes wrong at the third SOP which is a polysplit. The polysplit is supposed to create a loop around the cube front to back, I selected one edge, set it to close and quad strips, right clicked, and it worked fine last night. Now, the loop isn't closed, and it's splitting the wrong edges. Even after fixing that all my edit SOPs are evaluating incorectly.

Can someone maybe tell me what I'm doing wrong? I was working with secure selection off the whole time… Is that it? I saved regularly, I have 21 backups of this file and they are all messed up, becuase like I said it all goes wrong at the third SOP. Should I set my original primitive to polygon mesh rather than polygon? Should I be locking SOPs as I work? I know I can solve this problem in the future by saving out as bgeo, then loading the geo and continuing, but I'd rather have the entire network available to me in one file…

Thaks in advance.

I am also new to Houidini, so my guess as to your malady may be off.
As far as I have been able to figure out, SOPs perform their operation with polygon/vertex order in mind. So if you create a 10x10 sphere, then append Edit pulling points #10, 23, 30, and 40. Then go back to sphere SOP and change sphere parameters, say to 12X12, the results of Edit SOP will be changed as points #10,23,30,and 40 are no longer the same points that you originally pulled on a 10x10 sphere. Does that make sence? So if you have SOP network and change something in an early tile, that change will propagate down the network, perhaps with undesirable results.
The concern that SOPs will not evaluate properly is always on my mind, so I routinely (every 10 SOPs or so) delete history, as to have a plain mesh.

Dave Rindner

Well thanks for the reply, but I already understood what you are saying. I think the problem has to do with my not using secure selection. When I was building this thing I didn't go back up my network and make changes to the SOPs. I just did it after I found the file was screwed to see if I could fix it. I guess I'm just going to have to keep deleting history as you suggest. I guess Houdini's workflow isn't completely nondestructive ops: Thanks David, good work on your model by the way.

So, I've started anew. Everything is good so far. I've done everything the same except I'm using a polygon mesh rather than a polygon cube, and I'm using ` for reslecting geometry rather than turning off secure selection. Maybe someone could help me understand a couple things. What exactly is secure selection used for, and under what circumstances do you want it turned off? Also, what's the difference between choosing polygon or polygon mesh? I noticed that polygons seem to have interior geometry when you increase the initial subdivisions, and also interior braces. They look like spring objects. Polygon Meshes however act like polygons in Max or Maya. Forgive me if these are stupid questions, I'm new to Houdini, and I really want to understand these things.

MichaelC
Also, what's the difference between choosing polygon or polygon mesh? I noticed that polygons seem to have interior geometry when you increase the initial subdivisions, and also interior braces. They look like spring objects. Polygon Meshes however act like polygons in Max or Maya.

Both the “polygon” and “polygon mesh” options in the Box SOP will generate polygons. If you middle click on the icon of the Box, it will tell you the number of primitives and what types - in these cases all polygons.

The difference you are seeing is likely when you turn on “Divisions” to try to get something with more pieces than a unit cube. The Polygon mode does the interior braces which you have noted, while the Polygon Mesh does what you expect. The reason for this is historical. The Lattice SOP requires the interior points to do its deformations, and in the pre-subd world the primary use of the box-sop-with-divisions was to feed the lattice sop. With Houdini 5.0 we added the Polygon Mesh option to match people's expectations.

As for the polysplit causing bad behaviour, I am sending you a private message as we would like to track down the source of this problem.

- Jeff Lait

Thanks for the polygon explanation.