check: http://en.wikipedia.org/wiki/Rotation_matrix

On Tue, Jul 7, 2009 at 1:41 PM, Achim Bornhoeft <achim@bornhoeft.org> wrote:
Hello Frank,
thank you for your prompt answer.

Am 07.07.2009 um 18:44 schrieb Frank Barknecht:

Hallo,
Achim Bornhoeft hat gesagt: // Achim Bornhoeft wrote:

I need to solve the following problem for different setups of room
distributions.

Given are x and y values between 0 and 100:

0/100        100/100
|      
|   x
|
|       x              
|____________
0/0          100/0

I would like to transform the same values mathematically in a way that
the result correspond to the coordinate system rotated 45 degrees
clockwise:

0/0---------0/100
|      
|       x
|
|   x          
|
100/0       100/100

Isn't this a rotation by 90 degrees shown here? :)

Sure you're right.

Anyway rotating a point is easier if you convert the coordinates to polar
coordinates (radius and angle) first, then add the rotation angle to the
current angle and convert back.

You could do the math yourself, but in Zexy there are some handy abstractions
that do it for you: [cart2pol], [pol2cart] convert between cartesian (x,y) and
polar (r, phi) coordinates:

x   y
|   |
[cart2pol]
|   |
|   [+ 0.785398] add rotation angle: 0.785398 is 45 degrees converted to rad
|   |
[pol2cart]
|   |
x'  y'

The phi-angles are specified in rad, not in degrees. If you want to use degree
for the rotation angle, the [deg2rad] object is helpful and it's also part of
zexy. Or make your own: rad=deg*pi/180

I tried this but without the results I expected.
Probably it was not very clear how I explained it.
See attached patch for a better description of what I am looking for.

Achim






Ciao
--
Frank

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