# Help with vertex's in a 3d space

• July 4th 2011, 06:27 AM
Sneaky
Help with vertex's in a 3d space
I am making a 3d editing program and I need help with vertex points.

In a grid like this
http://kylepower.files.wordpress.com/2007/11/axis.jpg

given a point say (-20,-30,50), how would I get the new point if that point were to be rotated say 50 degrees along the y axis plane?

so the y plane would look like a vertical wall in the center of the grid. (so you know, its the y plane)

I figure if I had a 3d model and knew all its vertex's, then edited them all, and viewed the new model, the whole model would be rotated 50 degrees along the y plane.

thanks
• July 4th 2011, 10:21 AM
skeeter
Re: Help with vertex's in a 3d space
y-plane? there are an infinite number of planes that contain the y-axis. using your sketch, the vertical plane that contains the y-axis would be the y-z plane.
• July 4th 2011, 12:15 PM
Sneaky
Re: Help with vertex's in a 3d space
Yeah but I think I see what you mean.
Here is a new picture. This is what you mean by y-z plane?

Anyways I figure I have to use something like this:
Code:

 for i=1 to nrpoint ;or what ever :) x#=x_ponit(i) y#=y_ponit(i) z#=z_ponit(i) ; rotate x-axis x1#=x# y1#=(cos(ang)*y#)+(sin(ang)*z#) z1#=(sin(ang)*z#)-(cos(ang)*y#) ;roate y-axis x2#=(cos(ang)*x1#)+(sin(ang)*z1#) y2#=y1# z2#=(sin(ang)*z1#)-(cos(ang)*x1#) ;rotate z-axis x1#=(cos(ang)*x2#)+(sin(ang)*y2#) y1#=(cos(ang)*y2#)+(sin(ang)*x2#) z1#=z2# x_ponit(i)=x1# y_ponit(i)=y1# z_ponit(i)=z1# next
• July 4th 2011, 12:42 PM
HallsofIvy
Re: Help with vertex's in a 3d space
If you mean "rotate around the y-[b]axis[b]", not "y-axis plane", then any rotation about the y-axis, through angle [itex]\theta[/tex] changes (x, y, z) into (x', y', z') given by
$\begin{bmatrix}x' \\ y' \\ z'\end{bmatrix}= \begin{bmatrix}cos(\theta) & 0 & -sin(\theta) \\ 0 & 1 & 0 \\ sin(\theta) & 0 & cos(\theta)\end{bmatrix}\begin{bmatrix}x \\ y \\ z\end{bmatrix}$
• July 4th 2011, 01:57 PM
Sneaky
Re: Help with vertex's in a 3d space
hmm ok but how do I compute that, can you write each one out as a line rather than as a matrix, and also what are the matrix's for rotating around the x-axis and z-axis?