Re: A86: polygons


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Re: A86: polygons




The char theta represents an angle.  thetaX is how many degrees to rotate
around the X axis.  You can rotate different amounts around all 3 axis' to
get any POV.

At 10:00 AM 7/20/98 -0700, you wrote:
>
>Yeah I get most of it.  But, what are "thetaX","thetaY".
>I know what the character looks like but what effect does
>it have on x and y?
>
>Tnx
>
>> To do 3D rotations you can use matrix multiplication.  I frequently get
>> this backwards, so be careful:-).
>> 
>> Rotate about the x-axis:
>> [[1, 0,           0]
>>  [0, cos(thetaX),-sin(thetaX)]
>>  [0, sin(thetaX), cos(thetaX)]]
>> 
>> Rotate about the y-axis:
>> [[ cos(thetaY), 0, sin(thetaY)]
>>  [ 0,           1, 0]
>>  [-sin(thetaY), 0, cos(thetaY)]]
>> 
>> Rotate about the z-axis:
>> [[cos(thetaZ),-sin(thetaZ), 0]
>>  [sin(thetaZ), cos(thetaZ), 0]
>>  [0,           0,           1]]
>> 
>> the rotation matrix is multiplied by the (X,Y,Z) coordinates in the form:
>> 
>> [[cos(thetaZ),-sin(thetaZ), 0]     [[X]      [[Xcos(thetaZ)-Ysin(thetaZ)]
>>  [sin(thetaZ), cos(thetaZ), 0]  *   [Y]   =   [Xsin(thetaZ)+Ycos(thetaZ)]
>>  [0,           0,           1]]     [Z]]      [Z]]:
>> 
>> x = (Xcos(thetaZ)-Ysin(thetaZ))*25/(25-Z)
>> y = (Xsin(thetaZ)+Ycos(thetaZ))*25/(25-Z)
>
>-- 
>Tercero	 --  Email: mailto:tercero@busprod.com
>
>"The stone the builders rejected has become the capstone;"
>			--Psalms 118:22
>"Everyone who falls on that stone will be broken to pieces,
>but he on whom it falls will be crushed."
>			--Luke 20:18
>

--
David Phillips
mailto:electrum@tfs.net
ICQ: 13811951
AOL/AIM: electrum32


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