[vtkusers] How to get angle between two 3D points

[Arindam]

Thanks for your reply.I already tried and i got the angle by this.but i 
was getting one issue here.vtkMath is having a method called Dot 
<http://www.vtk.org/doc/release/5.0/html/a01710.html#z331_0> (const 
double x[3], const double y[3]) and Norm 
<http://www.vtk.org/doc/release/5.0/html/a01710.html#z333_0> (const 
float x[3]) in c++.but i was doing my application in c#.Where this two 
method prototype is like Dot(IntPtr X,Intptr Y) and Norm(Intptr X) . How 
can we convert it?Please help.

On 4/22/2013 8:35 PM, Marco Nawijn wrote:
> As the other Marco already mentioned, you need at least three points 
> (or 2 vectors) to calculate the angle between them.
> If you have them, you can simply apply the cosine rule which states 
> (in words):
> the cosine of the angle between two vectors is the dot product of the 
> vectors divided by the their lengths multiplied.
> so in math:
>                           dot(a,b)
>    cos(angle) =   -----------
>                         norm(a)*norm(b)
> I have not checked it, but I guess vtk will have buildin functions for 
> calculating dot (or inner) products and norms.
> Take a look at the functionality provided in the vtkMath library.
> Kind regards,
> (another) Marco
>
>
> On Mon, Apr 22, 2013 at 10:23 AM, Marco Sambin <m.sambin at gmail.com 
> <mailto:m.sambin at gmail.com>> wrote:
>
>     Hi.
>     In order to define an angle, you will need at least THREE points.
>     Is the third point the origin (0,0,0) in your case?
>     I guess you will need to identify the plane "containing" those
>     three points, and then you will be able to compute the angle on
>     that plane, in a "2D fashion".
>     Regards,
>
>     Marco
>
>
>
>     On Mon, Apr 22, 2013 at 10:19 AM, Arindam
>     <arindam at triassicsolutions.com
>     <mailto:arindam at triassicsolutions.com>> wrote:
>
>         Hi,
>
>         I want to calculate anglebetween two 3D points.Suppose the
>         points are (5,5,5) and (1,2,3). For 2D points i know how can i
>         do this.But for 3D points i need help from some one.Any help
>         will be appreciated.
>
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