The simplest way to control orientation is provide two vector attributes on your template points: N and up. Typically you don’t want all of your copies oriented the same way. There are easy attributes to use, like pscale, which uniformly scales each copy, but here we’re going to go into some of the trickier ones. Objects going into a copy SOP must be oriented to +Z. Here’s a little gif to show you the typical alignment vs the correct alignment: This typically means that your objects are going to need to be rotated 90 degrees on the X axis if they’re aligned the usual way, standing up along the Y axis and facing towards Z. The Copy SOP assumes that your object to be copied is aligned to the +Z axis. But there’s always going to be times where you need specific orientations for copies, and these times are when you’ll need a more thorough understanding of what the Copy SOP is doing under the hood… Orienting Copiesįirst things first. Now, in many situations, you can get by with just using the Attribute Randomize SOP to randomly generate an N attribute for you, and a random float for pscale, and you’re good to go. For common attributes you typically don’t need to include them in your Wrangles, and you never need to use them when writing group masks.) (Keep in mind that those little prefixes in front of the attribute names are only used in Wrangle nodes… they’re just there to hint to Houdini what attribute type they are. (another quaternion that defines an additional rotation).(a QUATERNION that defines the orientation of each copy.(a vector that can scale each axis independently).and (these vectors work together, explained later).You can view the complete list here: The important ones to remember are: Aside from the obvious position of each point, P, there are a few other attributes with obvious effects. One of the first things to learn about the Copy SOP is that the point attributes on the points you’re templating to can influence how each copy is placed in the world. I’m admittedly not great at math, so hopefully I can explain everything both intuitively and in such a way that I don’t completely embarrass myself in front of people who actually know what they’re talking about (i.e. Houdini’s documentation can admittedly be a little vague at times, but more importantly they expect you to have a decent understanding of how some fundamentals of computer graphics work, like how a 3×3 matrix works for orientation. “Why am I not supposed to copy stamp anymore?” “How do I randomly change what objects get instanced?” “How do I rotate each copy along a specific axis?” “How do I randomly rotate/scale my copies?” The most common questions asked seem to be: On the Houdini Discord server(s) I keep seeing the same kinds of questions over and over again, mostly related to instancing. An updated version of this article is now available here:
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