Matrix Rotation About Origin
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From: Matt Thomas on 14 Jul 2010 13:23 Hi All - I have a matrix that I need to rotate a specified number of degrees about the x,y origin. I have found resources for matrix rotation for 90 degrees but I need a way to do it a user specified amount (say, for example, 5 degrees). Can anyone point me in the right direction? Thanks! matt
From: Matt J on 14 Jul 2010 13:34 "Matt Thomas" <matt.at(a)gmail.com> wrote in message <i1krpq$iuc$1(a)fred.mathworks.com>... > Hi All - > > I have a matrix that I need to rotate a specified number of degrees about the x,y origin. I have found resources for matrix rotation for 90 degrees but I need a way to do it a user specified amount (say, for example, 5 degrees). ====== If you have the Image Processing Toolbox, you can use imrotate(). Otherwise, you might have to fall back to interp2().
From: Andy on 14 Jul 2010 13:45 "Matt Thomas" <matt.at(a)gmail.com> wrote in message <i1krpq$iuc$1(a)fred.mathworks.com>... > Hi All - > > I have a matrix that I need to rotate a specified number of degrees about the x,y origin. I have found resources for matrix rotation for 90 degrees but I need a way to do it a user specified amount (say, for example, 5 degrees). > > Can anyone point me in the right direction? > > Thanks! > > matt It sounds like you found rot90? FYI, I do not think it means what you think it means.
From: Ben on 14 Jul 2010 09:47 function [m] = rotmat(a,b,c); %calculates the rotation matrix in order XYZ in a right handed system %the coordinate system is rotated, not the points! ca=cos(a); sa=sin(a); cb=cos(b); sb=sin(b); cc=cos(c); sc=sin(c); m1=[1 0 0;0 ca -sa;0 sa ca];%rotation only about x axis m2=[cb 0 sb;0 1 0;-sb 0 cb];%rotation only about y axis m3=[cc -sc 0;sc cc 0;0 0 1];%rotation only about z axis % m1=[1 0 0;0 ca sa;0 -sa ca]; % m2=[cb 0 -sb;0 1 0;sb 0 cb]; % m3=[cc sc 0;-sc cc 0;0 0 1]; m=m1*m2*m3; succes
From: Ravi on 14 Jul 2010 14:28
Hi Matt, If your matrix is a 1-D column vector, the problem is of coordinate transformation. If your matrix is a 2D matrix that represents a tensor (such as stress, moment of inertia), the problem is of tensor transformation. Let it be desired to transform from base to target coordinate system. Let T= nxn orthogonal transformation matrix from base to target coordinate system (explained below) 1-D column vector: X0= nx1 column vector in base coordinate system X = nx1 column vector in target coordinate system Then X=T*X0 2-D tensor matrix : K0= nxn tensor matrix in base coordinate system K = nxn tensor matrix in target coordinate system Then K=T*K0*T' where T' is the transpose of T Transformation Matrix T: Transformation Matrix T is problem-dependent orthogonal matrix (inverse of T=transpose of T). The rows of T are the direction cosines of the axis of the target coordinate system with respect to the base coordinate system. For example, if it is desired to rotate about the Z-axis of the base coordinate system, T=[ cos(angle) sin(angle) 0 cos(angle+pi/2) sin(angle+pi/2) 0 0 0 1 ] where angle=rotation angle If you need to rotate about X or Y-axis, modify T appropriately. Hope this helps ! Ravi "Matt Thomas" <matt.at(a)gmail.com> wrote in message <i1krpq$iuc$1(a)fred.mathworks.com>... > Hi All - > > I have a matrix that I need to rotate a specified number of degrees about the x,y origin. I have found resources for matrix rotation for 90 degrees but I need a way to do it a user specified amount (say, for example, 5 degrees). > > Can anyone point me in the right direction? > > Thanks! > > matt |