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Old 05-17-2013, 06:38 AM   #1
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Masanori Tsutsumi
Tokyo, Japan
Join Date: Jun 2009
Posts: 1
Calculate angle from vector.

Hi,I'm trying to calculate angle from vector. It seems simple.

my test code is here:
proc test(){ vector $a = <<0, 1, 0>>; vector $b = <<0.5, 0.5, 0>>; float $c = $a * $b; float $mag_a = mag($a); float $mag_b = mag($b); float $theta = ($a*$b)/($mag_a * $mag_b); $theta = $theta * 180 / 3.14; print ("theta = " + $theta + "\n"); }test;

theta = 40.53478363

I think it`s 45.0 in mathematically,but The result ange is uncorrect.
It`s nearly 45.0 .
Is there are any items missing? or formula is uncorrect?

Please give me advice.

Sorry for my poor English.
Old 05-27-2013, 01:52 PM   #2
hazmondo's Avatar
Rigging TD
Axis Animation
Glasgow, United Kingdom
Join Date: Jan 2013
Posts: 329

It seems like your saying that θ = (a*b)/(|a|*|b|) but that equation is incorrect, the correct equation is cosθ = (a*b)/(|a|*|b|) --> θ = arccos((a*b)/(|a|*|b|)).

Hope this helps,

Last edited by hazmondo : 05-27-2013 at 07:00 PM.
Old 06-15-2013, 02:14 PM   #3
Nathaniel Anozie
Baltimore, USA
Join Date: Dec 2008
Posts: 70
Hi, if using Maya might want to checkout the built-in angleBetween Node or MEL/Python command. Hope this is helpful.

Old 06-21-2013, 10:40 PM   #4
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Geordie Martinez
Character TD - Rigger - Massive TD
Industrial Light & Magic
San Francisco, USA
Join Date: Jun 2003
Posts: 437
PyMEL could really clear this up in a quick way. here is what you were doing. it was indeed 45 degrees:

import pymel.core as pm # make vectors vec1= pm.dt.Vector(0,1,0) vec2= pm.dt.Vector(0.5,0.5,0.0) # get angle between in radians radians = vec1.angle(vec2) #get degrees degrees = pm.dt.degrees(radians)
Check out my "Intro to PyMEL Training Video" at -- maya python the OOP way!
Old 06-21-2013, 10:40 PM   #5
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