Reset Scale of a matrix

#1

Is it possible to reset the scale of a matrix the same way as ResetScale $ works for objcets?

Here is an example:

(
	mat01 = (matrix3 [-0.95407,0.14169,-0.263958] [-0.211014,-0.943264,0.256371] [0.212657,-0.300295,-0.929839] [-2.59766,-51.5166,16.7929])
	format "mat01 scale: % \n" mat01.scale  --> [-1,-1,-1] 
	
	p = point transform:mat01
	ResetScale p
	
	mat02 = p.transform
	format "mat02 scale: % \n" mat02.scale  --> [1,1,1] 
	
	--	"mat02 is the desired result - scale is [1,1,1] and the axes directions are not changed"
	-- (matrix3 [0.95407,-0.14169,0.263958] [0.211014,0.943264,-0.256371] [-0.212657,0.300295,0.929839] [-2.59766,-51.5166,16.7929])

)
#2

Based on this documentation:

http://docs.autodesk.com/3DSMAX/16/ENU/3ds-Max-SDK-Programmer-Guide/index.html?url=cpp_ref/class_matrix3.html,topicNumber=cpp_ref_class_matrix3_htmld2df3bd8-83a6-4a09-8d56-0224c70b7b99

You want to multiply by a matrix containing the inverse of your current scale to ‘undo’ the scale and set it back to 1:

mat01 = (matrix3 [-0.95407,0.14169,-0.263958] [-0.211014,-0.943264,0.256371] [0.212657,-0.300295,-0.929839] [-2.59766,-51.5166,16.7929])
format "mat01 scale: % \n" mat01.scale  --> [-1,-1,-1] 
normalizer = (matrix3 [1/mat01.scale.x,0,0] [0,1/mat01.scale.y,0] [0,0,1/mat01.scale.z] [0,0,0])
mat01 = mat01 * normalizer
format "mat01 scale: % \n" mat01.scale --> [1,1,1]
#3

Hi!

Maybe I am doing something wrong, but your code changes the direction of the axes of the point helper. Check this:

(

	mat01 = (matrix3 [-0.95407,0.14169,-0.263958] [-0.211014,-0.943264,0.256371] [0.212657,-0.300295,-0.929839] [-2.59766,-51.5166,16.7929])
	format "mat01 scale: % \n" mat01.scale  --> [-1,-1,-1] 
	
	p = point transform:mat01 wirecolor:red axistripod:true cross:false
	
	
	normalizer = (matrix3 [1/mat01.scale.x,0,0] [0,1/mat01.scale.y,0] [0,0,1/mat01.scale.z] [0,0,0])
	mat01 = mat01 * normalizer
	format "mat01 scale: % \n" mat01.scale --> [1,1,1]
	p1 = point transform:mat01 wirecolor:yellow axistripod:true cross:false
	
-- 	ResetScale p
-- 	
-- 	mat02 = p.transform
-- 	format "mat02 scale: % \n" mat02.scale  --> [1,1,1] 
	
	--	"mat02 is the desired result - scale is [1,1,1] and the axes directions are not changed"
	-- (matrix3 [0.95407,-0.14169,0.263958] [0.211014,0.943264,-0.256371] [-0.212657,0.300295,0.929839] [-2.59766,-51.5166,16.7929])

)

The X, Y, Z axis of the point helper should points in the same direction as before to reset the scale of the mat01.

#4

orthogonalize p.transform

produces the same result

#5

@Klvnk’s solution is definitely better!

Matrix math is always tricky - each system is a little different in terms of how they implement it - how they build their matrices and the order of matrix multiplication. I’m guessing for the math I gave you that you would need to flip the multiplication order (matrix multiplication is non-commutative) or something else simple. Since it’s already solved, I won’t bother fixing it :slight_smile:

#6

another alternative is

mat02 = mat01.rotationpart  as matrix3;
mat02.translation = mat01.translation;
#7

Thank you, guys. :slight_smile: