# translation matrix

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giugio    246
Hy. I have created with gamedev forum help a rotation matrix starting from AxisY, direction and position vector like: C3DMatrix R; R.m_Z = vAxisY; R.m_Y = (vAxisY ^ vDirection).Normalize(); R.m_X = R.m_Y ^ R.m_Z; R.m_Z is a vector with the last vector in a 3x3 matrix. R.m_Y is a vector with the center vector in a 3x3 matrix. R.m_X is a vector with the first vector in a 3x3 matrix. operator ^ is the cross product. all work fine , a point multiplied by this matrix change his rotational components correctly,thanks , but now i must create the translation matrix and i have the position vector . How? Thanks.

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haegarr    7372
Quote:
 Original post gy giugionow i must create the translation matrix and i have the position vector. How?
That depends on the structure of C3DMatrix. Does it have something like C3DMatrix.m_W? If so, than it is a good candidate. If, on the other hand, C3DMatrix is a 3x3 matrix only, then it is not able to represent translation at all.

Further, notice please that setting rotation and translation independently has a specific geometrical interpretation. Make sure that it is actually what you want. Perhaps you have to rotate the translation before setting it into the matrix.

BTW
Quote:
 Original post gy giugioa point multiplied by this matrix change his rotational components correctly
What's the rotational part of a point? There is usually nothing like that at all.

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giugio    246
no , there aren't C3DMatrix.m_W.
IS possible to construct a regular 3x3 matrix with the translation ?
How i can create the translation 3x3 matrix for transform independently ?
Thanks again haegarr.
by

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haegarr    7372
From your original post it seems me we're speaking of 3D space. In 3D space you use at least a 3x3 matrix for rotation (and perhaps scaling and shearing). But you cannot incorporate translation in it. On the other hand, if you have a 4x3 or a 4x4 matrix, then translation can be incorporated.

If the 3x3 matrix is all you have, then translation must be done manually by addition. E.g.
R * v + t
where R is the rotation matrix, v the position vector, and t the translation vector. Notice please that this is correct for position vectors only. For direction vectors the formula has to be reduced to
R * v
because direction vectors have no location property.

Perhaps you should look out for a "C4DMatrix" or the like? Are you working with your own math library, or are you using a foreign library?

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Evil Steve    2017
What you're asking is the same as: "I have a single float. How do I make that float into a rotation matrix"?

You can't - To do translation you need at least a 4x3 matrix. You only have a 3x3 matrix, there's no space in it for a translation.