# How to compute direction for animate light

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Hi All Member on this forum.... I have question and hope you can help me Using Maya and create animate light. I get an 4x4 matrix as: m11 m12 m13 m14 m21 m21 m23 m24 m31 m32 m33 m34 m41 m42 m43 m44 For m41, m42 and m43, as i know, these are position of animate light. and as i also know,we can use the child matrix (3x3 matrix): m11 m12 m13 m21 m21 m23 m31 m32 m33 to compute the direction of this animate light(direction.x , dierction.y and direction.z). My question are: How to compute direction of this animate light. If you know, please share with me (formula or same...) Thank for your help! Paul

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The 3x3 rotational part of a matrix can be thought of as 3 vectors, right, up, and at, which are the local X, Y, and Z axes. You want to extract the at vector. It will be either row 3 or column 3 depending on if your matrix is built as world matrix or a view matrix, ie: (m13, m23, m33) or (m31, m32, m33).

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