# Calculate target pos from transform matrix and distance to target.

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Part1

I have a camera. It is specified by 4x4 matrix from XML.
Also I have scalar value “distance to target”.
I need to calculate the target pos.

First step: calculate cameraPos and direction quaternion.

XMMATRIX M = LoadMatrixFromXML();
XMVECTOR scale, rotationQuaternion, cameraPos;
XMMatrixDecompose(&scale, & rotationQuaternion, &cameraPos, M);


Question1:
How to calculate position of a target, if I have cameraPos, distanceToTarget and rotationQuaternion?

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Part2.

I found many sources about what are quaternions, vectors, matrices and the math that is behind of them.
I found a lot of DirectXMath functions in MSDN.
But I can’t find a missed link between them: how to link math tasks like I am struggled with the DirectXMath library.

Quesion2:
Can anyone share a good connection link between math tasks and how are they can be solved with DirectXMath library?

It might be a link to a book, url, ....

Edited by Happy SDE

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So your camera is pointing at the target, you have it's rotation, you have the distance to the target and you have the camera's position?

It should be a case or rotating your 'forward' vector by the rotation, multiplying it by the distance and adding it to your camera's position. It's been a while since I have done anything like this but it should be along the lines of:

toTarget = rotation*forward;

targetPos = cameraPos + toTarget  * distancetoTarget;

Forward will be just whatever is considered the default forward in the space you use (I think for DirectX is would be (0, 0, 1) but I could be wrong. toTarget is just the forward vector rotated by the rotation.

Edited by Nanoha

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Thank you, Nanoha!

It works.

The vector (0,0,1) is exactly the view direction.

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