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*On 03/03/2010 at 18:21, xxxxxxxx wrote:*

Do I need the world coordinates of the points I am using for this to work properly?

~Shawn

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*On 03/03/2010 at 18:21, xxxxxxxx wrote:*

Do I need the world coordinates of the points I am using for this to work properly?

~Shawn

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*On 09/03/2010 at 17:20, xxxxxxxx wrote:*

I feel like I have done the rotation matrix correctly here. But my object is not rotating to the normal of the polygon. Does anyone see anything that I am doing wrong creating the rotation matrix?

I would GREATLY, appreciate any help anyone could offer. This one is irritating me because everything I have read about rotation matrices says that I am doing it right. I am using a vector that represents the center of the polygon (polygonLocation) I am using another point in the polygon to determine the plane upon which the polygon rests. I am then using the cross product of those vectors to determine the up vector that is perpendicular to the plane. So, if my understanding of rotation matrices is correct, this should create a rotation matrix that can then be adapted by an object and that object should rotate to the normal of the polygon.

However, that is not happening with what I have pasted above. I am at a loss. Does anyone see anything that I am doing wrong?

Thanks so much for anyone who has the time to help me out.

~Shawn

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*On 15/03/2010 at 01:25, xxxxxxxx wrote:*

Originally posted by xxxxxxxxI am using a vector that represents the center of the polygon (polygonLocation) I am using another point in the polygon to determine the plane upon which the polygon rests. I am then using the cross product of those vectors to determine the up vector that is perpendicular to the plane.

This part is wrong.

Assume that A is the midpoint of your polygon and B is one of the polygon points.

N is the polygon normal.

You have to build the cross product of (B-A) and N for one of the matrix axes, let's say for V1.

Then build the cross product of this new axis and the normal for the second matrix axis, V2.

The normal is the third axis of the matrix, V3.

The polygon midpoint is the matrix offset, V0 or off.

cheers,

Matthias

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*On 15/03/2010 at 02:41, xxxxxxxx wrote:*

Thanks Matthias,

I must not fully understand how to get the normal then. I thought that the normal was A - B. How to I get the value for N then?

THanks,

~Shawn

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*On 15/03/2010 at 02:47, xxxxxxxx wrote:*

Would I use

~Shawn

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*On 15/03/2010 at 02:49, xxxxxxxx wrote:*

For triangles the normal is the cross product of two edges of the triangle. For quadrangles it's not exactly defined. The easiest way which gives a good result is too use the cross product of the diagonales.

PS. please read up on 3D geometry basics, it will help you in the long run. Most of it can be found through Google and Wikipedia.

cheers,

Matthias

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*On 15/03/2010 at 03:06, xxxxxxxx wrote:*

So to calculate the normal of a quad would I do something like this... Assuming that the points in a quad are A, B, C, and D

QUAD

N = (A-C)%(D-B)

TRIANGLE

N = (A-C)%(B-C)

SOmething like that?

Does CalcFaceNormal() do this for you? or is that something completely different?

Thanks a lot for your help,

~ Shawn

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*On 15/03/2010 at 03:23, xxxxxxxx wrote:*

yes and yes

source code of CalcFaceNormal()

```
inline Vector CalcFaceNormal(const Vector *padr, const CPolygon &v)
{
if (v.c==v.d)
return !((padr[v.b]-padr[v.a])%(padr[v.c]-padr[v.a]));
else
return !((padr[v.b]-padr[v.d])%(padr[v.c]-padr[v.a]));
}
```

cheers,

Matthias

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*On 15/03/2010 at 12:00, xxxxxxxx wrote:*

does CalcFaceNormal work for you?? when i use it i get only nonsense rotations.

cheers,

ello

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*On 15/03/2010 at 12:32, xxxxxxxx wrote:*

What are you trying to do?

~Shawn

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*On 15/03/2010 at 12:41, xxxxxxxx wrote:*

i am just trying to rotate some clones according to a surface normal. and using CalcFaceNormal results in this:

http://tempfiles.earthcontrol.de/nm01.jpg

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*On 15/03/2010 at 12:56, xxxxxxxx wrote:*

hmmmm... what are you using for the "padr" and for "v"... ?

in

CalcFaceNormal(padr, v)

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*On 15/03/2010 at 13:05, xxxxxxxx wrote:*

i am using this:

```
padr = ToPoint(baseMesh)->GetPointR();
v = ToPoly(baseMesh)->GetPolygonR();
```

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*On 15/03/2010 at 13:12, xxxxxxxx wrote:*

are you creating a rotation matrix based on a specific polygon. ? When I get home I'll show you how I am doing it. I'm driving home right now.

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*On 15/03/2010 at 13:17, xxxxxxxx wrote:*

no, i am just using clone->SetRot(normal);

is this wrong??

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*On 15/03/2010 at 13:41, xxxxxxxx wrote:*

I'm pretty sure that if you are trying to rotate objects based on a polygon then you will need to create a rotation matrix for that polygon and then make the matrix of the object you want to rotate equal to the rotation matrix. That's how I understand it.

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*On 15/03/2010 at 13:51, xxxxxxxx wrote:*

well, what is so strange is that it works for spheres, but not for terrain objects:

http://tempfiles.earthcontrol.de/nm02.jpg

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*On 15/03/2010 at 14:20, xxxxxxxx wrote:*

Here's how I am doing it.

```
//ROTATION MATRIX
//GetPoints
Vector c = polyLocation; //midpoint
Vector p = points[lngA]; //polygon point
Vector n = CalcFaceNormal(points, selectedPoly[lngI]); //normal
Vector scale = Vector(Len(opMatrix.v1), Len(opMatrix.v2), Len(opMatrix.v3)); //Get Scale
//Contruct Matrix
Matrix rotMatrix;
rotMatrix.off = p; //The base of the matrix
rotMatrix.v1 = !((p - c)%n); //X axis points toward the second point
rotMatrix.v2 = !(rotMatrix.v1 % n);//Y Axis is perpendicular to the X axis
rotMatrix.v3 = !(n); //Z Axis is along the normal
rotMatrix.v1 = !(rotMatrix.v1 * scale.x);
rotMatrix.v2 = !(rotMatrix.v2 * scale.y);
rotMatrix.v3 = !(rotMatrix.v3 * scale.z);
//place the first object within the rotation matrix
firstSelection->SetMg(rotMatrix);
firstSelection->SetPos((opMatrix * polyLocation));// + firstSelection->GetRad().x);
```

This is working quite well now.. creating a rotation matrix gives me the exact rotation of that specific polygon.

Hope this helps you.

~Shawn