Blender's Coordinates/Angles?


(clausawits) #1

I’m looking for info on how Blender calculates the angles of an object.

Specifically, I created a sword that consists of merely two cylinders, scaled and with creases added to the subsurf. (Just something quick and dirty to play around with animating using nozzy’s skinny guy…) I added the second cylinder in EDIT mode, so in Object mode, they both select as one thing.

Anyway, when I hit NKEY (in Object mode), the transform properties list:
RotX: 68.593
RotY: -0
RotZ: 48.981

But, the “sword” is straight up and down according to side, front, and top views. I put the cylinders in from the top view, and did some slight moving of vertices in Edit mode to ensure that the “blade” cylinder and “hilt” cylinder are coaxial… <edit, clarification: I grabbed all the vertices of the “hilt” cylinder with a BKEY select, and shifted them to be directly in line with the “blade” cylinder>

So what’s up with those 69 and 49 degree rotations listed?

When I append the object into skinnyguy.blend and try to scale it, things go completely funky with the object rotating as well as scaling… ??? Is there any way to fix this? Or am I screwed, and have to start over from the beginning? (starting over isn’t a big deal with this particular instance, but I’d be royally put out if this happened after modelling something complex/difficult)

Many thanks…
(edit: grammar)


(Duoas) #2

Did you add the object while viewing orthogonally (top, front, or side)?

Chances are that the object itself is twisted even though the mesh vertices align with the view.

Go into Object Mode, select the object, and press Ctrl-A --> Apply Size and Rotation. Now your object should be aligned Rot<0,0,0> (and Size<1,1,1>).

Does this help?


(clausawits) #3

Well, as I said, I added the cylinders while in Top View, NP7, so I wouldn’t expect anything to have been twisted… but, the CTRL-A did the trick, many thanks…

I guess CTRL-A is what you hit when you want to say “This is the new normal”, right?

Thanks again…


(macouno) #4

The thing you have to remember is you have 2 things.

  1. The object (the pink dot in your 3d window)

  2. Whatever is in (or connected to) the object

In your case 2 is a mesh, but it could also be a lamp/armature/path, well anything.

Whatever is in the object can be rotated sepparate from the object itself (like a mesh in edit mode).

So in your case, where everything looks straight. you actually have your object rotated 68.593 degrees around it’s x axis, but you have your mesh rotated -68.593 degrees relative to the object. Thus it looks straight but it isn’t.

With apply size/rotation what happens is the object is rotated to 0 and the mesh is rotated to the original object rotation… so for the mesh -68.593 + 68.593 = 0 degrees as well, and everything is straight.

A normal is only a vector, a vector is 3 lengths that describe one position in 3d space relative to another one. A vector can point to a specific point in space but it can also describe a direction. So nope a normal isn’t a rotation exactly.

Hope that clears it up somewhat.


(Duoas) #5

Hmm, also, if you’re viewing in perspective that will throw-off the orientation even if you’ve pressed 1, 3, or 7 on the numeric keypad.

In the ‘View and Controls’ section of the User Preferences window you can select ‘Auto Perspective’ to have Blender automatically switch between orthographic and perspective modes…

Glad I was of help.


(clausawits) #6

I guess what threw me is that I don’t see how it’s possible for a pair of cylinders that are coaxial along the Z-axis to have a Rotation on two axes. Sure, you can have some rotation about the Z-axis, and still have everything vertical, but also about the X axis? Also, I never issued a rotation command during creation/editing-- only translation (GKEY), and only to one cylinder (the whole cylinder at once), one time, and only on one axis. 69 and 49 degrees are angles that aren’t easily mistaken for 0 degrees…

Also, does Blender use an Euler angle convention?

Duoas, I am fairly certain that I was not looking at things in perspective… the NP5 key toggles perspective on and off, no?

Anyway, I’ve learned about CTRL-A now… I hope I can remember it when I need it next. Thanks again for the help!