I normally think this is easy in 2d, but now I am a bit stuck..

I have a 3d-Vector with the length 1
I have rotation in XYZ
How do I get the position of the vector3

TG Viking:

I have a 3d-Vector with the length 1
I have rotation in XYZ
How do I get the position of the vector3

I'm not quite understanding. You have a Vector3 that contains the rotation of an object, and you want to extract the position from it? Vector3s can only hold one type of data at a time - if you're using it for rotation then I don't see how you could also fit position in there.

Are you thinking of a Matrix, which can hold position, rotation and scale? If so, it is very difficult to extract anything out of it once it's inside the matrix.

What I would do is keep the position and rotation as Vector3s, and combine them into a Matrix when you need to render.

Or am I misunderstanding the problem?

The formula will look something like:

Vector3 Rotation; //Known value
float Length = 1; //Known value

Vector3 position; //I want to calculate this

position.X = (float)Math.Sin(Rotation.Z) * Length;
etc.

I see now. I'm not sure if there's a built in way of doing that (I haven't seen one), but here's one way I thought of to do that:

Create a matrix from your rotation and get the forward position, move your object by that amount * length, and then use the resulting position.

Is that what you need?

Thanks a lot! It does almost work now, I still got some weird bug, but I think I will figure it out.

Ok, it looks like Matrix.Forward only moves the object in two dimensions, it doesn't matter what Rotation.Z is, the outcome is always the same.

Interesting! I didn't know that. That could explain a very weird bug I was having a while ago.

Maybe you can use a combination of Matrix.Forward and Matrix.Down?

Solved!

I works now, don't really know what I did wrong but it works now. The goal was to make one 3d object(child) follow another(parent). I still doesn't work if the child have any rotation.

If you need to point something at another object, there's a great chunk of code in the FAQs that may help: link.

Glad you got it working. Problems like this make me miss the good old days of Blitz3D with it's PointEntity and MoveEntity commands...

Thanks a lot, rigth now I am trying to figure out how the child object should rotate when it's parent is rotating. I guess I should see the two object facing in two vector3-directions and use matrixes to add them together somehow.

childImage.Rotation = parent.Rotation + Rotation_Relative; //Wrong way to do it

Ubergeek: your signature "This signature is to big fore the 512-char limit", it looks like a error message made by the homepage, maybe you should write "Read more about me" instead, will make it look more apealing.

So you want the child object to have the same rotation of the parent object? If you're pointing the child at the parent then why would it matter how the parent is rotated? Or are you trying to intercept the parent like this:

C
  \
   \
    \
     \
P--->

If you want to add the rotation matrices together, then you can use Matrix.CreateFromYawPitchRoll for each of them, multiply them together, and if you need to use Matrix.Decompose to get a quaternion rotation out.

About the signature: it's supposed to be a joke; I thought it would be apparent since it's a link and is explained at the signature page... I'll give it some more thought and maybe come up with something better. Thanks for pointing that out!

Nope, I can not figure this one out, I guess I found the limit of my math knowledge. I better find some explaining homepages.

Edit: After reading through a big bunch of posts. And I got the feeling that I am on the completely wrong track here. People are talking about replacing position and rotation with a "quaternion" (new word for me) to make the math easier to get. Looks like i have to redo a big bunch of code *sniff

Edit2: Now have I exterminated all existing angles and replaced them with quaternions, and the the posters was right - everything is much easier now!

Should I post the correct code?

Yes please post.

And rather than changing the thread subject, just mark the thread as answered. :)

Jim Perry:

And rather than changing the thread subject, just mark the thread as answered. :)

It was like half a year ago I wrote the last post in this thread, surprised that it would be brought up again!

This how my code looks like now:
The child will always follow the parent in scale, rotation and position.