Theory Lesson C: "Origins" or "Why the world turns arouns a...point?"
This lesson is damn important and you'll be happy that you read this...or you aren't if you came back to read this after you tried lesson 5...
This lesson is especially important for animating a model. We're talking about "Origin Points" of Pieces.
An origin point is the point the object turns around. I'll also call it "rotation center" because that sounds easier sometimes... The animation scripter can't tell the object to "turn around 50 degrees and use the point XYZ as rotation center". He only has the possibility to say how far it turns and how fast it does that. So the information has to be stored inside the model file. And how we get it into the file I'll tell you the next lesson. This Theory lesson I'll tell you WHY we do that. It is VERY important that you understand this. Maybe you won't understand it until you made it wrong, but then you'll remember this lesson and know what I meant.... ;)
Let's start. First, I'll tell you something about TA axes. You need to imagine how you want to animate the pieces while you export your model out of Rhino, so I decided to tell you this before we come to animation scripting...
Here is a pic of how the TA angles are arranged. They are the same as in Rhino (only named different) if we export it properly. So, every object got an origin point it turns around. A turret of a tank should have the origin point in the middle of the turret (seen from the top) so that it can turn around the y-axis without looking weird. The barrel should be a seperate object so that it can turn up and down. The origin of the barrels should be where they are connected with the turret. Imagine that, in the drawing above, the origin point is in the center of the turret and the object is the beginning of the barrels. The unitmaker did set the origin point wrong, because the barrels lift up above the turret when aiming at air targets or shooting ballistic project. The result is a very weird looking animation. Given that the object is the beginning of the barrels (where they connect to the turret), the origin point (center of rotation) should be in the center of the "object" (at the beginning of the barrels).
But now there appears another question: When you turn the turret, and the barrels are seperate objects with another origin point, how can they turn together with the turret when it turns to aim? The solution: An object-tree. Here is a pic taken of the 3dobuilder:
You see the object tree in the upper-left corner? I'll talk about it now. But first, do you see that I marked the object "sleeve"(responsible for up/down aiming in this model)? And do you see the very small blue point at the tree wireframe viewports? (If not, look directly at the center of the top view and you'll see it...) It is the origin point (rotation center) of the "Sleeve" object.
Now for the object tree: You see that the sleeve is connected to the turret. You see that the barrels are connected to the sleeve.
If you turn the turret now around the y-axis to aim vertically, all objects connected to it will turn with it - and not around their own origin point, but around the origin point of the turret. Now the sleeve gets an order tu aim upwards. The barrels, which are connected to it turn with it around the sleeve's origin point. The turret is not affected by that.
The base is always the groundplate, some designers use it also to store the body.
This is very hard to understand, and I don't want to talk about it forever - maybe you understood it now or you'll understand it later, we'll see. I only wanted to prepare you for what follows now...