Plane rotation ~ how on earth does it work?

Started by cyphyr, June 11, 2012, 10:37:06 AM

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cyphyr

Can some one point me to an explanation of the edge vector a and edge vector b rotation. For example what would an angle of 23deg rotation about the y axis be and more usefully, how do I go about working it out.
Cheers
Richard
www.richardfraservfx.com
https://www.facebook.com/RichardFraserVFX/
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Ryzen 9 5950X OC@4Ghz, 64Gb (TG4 benchmark 4:13)

Simius Strabus

Mighty good question. It would be a lot easier if the rotation worked with normal angles instead of something between 0-1. (next software update???)
Why stop dreaming when you wake up?

iMac i7 2.8GHz 8Gb


cyphyr

Thanks :)
That doesn't actually say how to rotate a plane to (as in my example) 23deg in the y axis.
Cheers
Richard
www.richardfraservfx.com
https://www.facebook.com/RichardFraserVFX/
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Ryzen 9 5950X OC@4Ghz, 64Gb (TG4 benchmark 4:13)

bobbystahr

pretty please make this work like a population where we can rotate around the Y...this rotation thing really inhibits me and I'm sure many others from using this otherwise useful object..
something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist

Oshyan

I'm afraid only Matt could explain the Plane rotation, the approach to those settings is definitely more for the mathematically minded! Unless you really need some capability of the built-in plane, you could of course just externally model and import one and then adjust it like a normal object...

- Oshyan

cyphyr

Hi Oshyan
I'm using a plane as a substitute for vertical cliffs which works very well. It'smuch easier to get good undistorted "cliff" displacements and textures. The problem is that I'm restricted to using it in angles of 90deg, (due to my limited understanding of the "Edge vector" concepts), which for my current project has some rather severe knock on issues ;)
Cheers
Richard
www.richardfraservfx.com
https://www.facebook.com/RichardFraserVFX/
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Ryzen 9 5950X OC@4Ghz, 64Gb (TG4 benchmark 4:13)

Matt

I am completely guilty of making this object more complicated than it should be. We are going to introduce a new object with v2.5 that has standard rotation parameters, can be used in populations, and is rendered in the same mode as "ray trace objects". The new object is called 'Card' if you're an alpha tester, but it's still a work-in-progress. We might also update the Plane object with standard rotation controls, since the Plane still has some unique abilities such as proper displacement in all rendering modes.

Richard, your example of a 23 degree rotation about the Y axis needs to be worked out using some trigonometry, which is as follows:

Rotate Y = 23:

Edge vector a = cos(23), 0, -sin(23)
Edge vector b = sin(23), 0, cos(23)

Set your calculator to degrees to calculate the following:

sin(23) = 0.3907311285
cos(23) = 0.9205048535

Plug this into the Plane:

Edge vector a = 0.9205048535, 0, -0.3907311285
Edge vector b = 0.3907311285, 0, 0.9205048535

Note the minus sign.

BTW, the maths might look like I'm rotating in the opposite direction from what you'll see in text books, but I'm matching the Y rotation in other TG objects, which is supposed to match the heading on a compass.

Now, if you want to rotate on the X or Z axes, here's the trig for those:

Rotate X = 23:

Edge vector a = 1, 0, 0
Edge vector b = 0, sin(23), cos(23)

Rotate Z = 23:

Edge vector a = cos(23), -sin(23), 0
Edge vector b = 0, 0, 1


Matt
Just because milk is white doesn't mean that clouds are made of milk.

cyphyr

Hi Matt
Thanks for the detailed answer. It's not my every day level of math but I think I can work my way around with the example.
Also I'd definitely like the option of standard rotation controls on the plane object. I tried the card object but as you say it lacks proper displacement.
Cheers and thanks for the quick answer.
Richard
www.richardfraservfx.com
https://www.facebook.com/RichardFraserVFX/
/|\

Ryzen 9 5950X OC@4Ghz, 64Gb (TG4 benchmark 4:13)

bobbystahr

I look way forward (from V 2.3.22.1 to V 2.5) to this and please keep the plane but with sane rotations for us maths impaired types
something borrowed,
something Blue.
Ring out the Old.
Bring in the New
Bobby Stahr, Paracosmologist


AndyWelder

Thank you for explaining this to a layman in maths, it saved my day: I tried to match a masked water plane to a "card trail" in order to get a water filled trail but because I didn't know how to rotate a plane there was always overlap with the plane used for a nearby puddle. With the help of the explanation above  and the build-in Windows calculator it was a piece of cake. :)
"Ik rotzooi maar wat aan" Karel Appel

Upon Infinity

Your best bet is to create a flat plane-like object in a third-party modeler.  See my post here:  http://www.planetside.co.uk/forums/index.php?topic=14861.0

This new object will be much easier to manipulate and rotate as all other imported objects.