[vtkusers] Distance between points

[David Gobbi]

You should try these other math methods to see if they also give
incorrect results:

  double dotprod = vtkMath.Dot(pP0, pP1);
  double norm = vtkMath.Norm(pP0);

For your values of p0 and p1, they should return:
dotprod: 643.77
norm: 25.3118549300520

On Tue, Jan 14, 2014 at 5:03 PM, Matias Montroull <matimontg at gmail.com> wrote:
> It is weird that it doesn't work in ActiViz... It's the same code, maybe it
> is the overload function you mentioned?
>
>
> On Tue, Jan 14, 2014 at 8:58 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> I just tried it in Python, and it works there just fine.  And you can
>> be sure that it works in C++, because it is one of the most-used
>> methods in VTK, and hundreds of the VTK tests would fail if it was
>> giving the wrong answer.
>>
>> The distances that I get are:
>>
>> p0 = (10.2, 20.7, 10.4)
>> p1 = (10.5, 20.5, 10.8)
>> vtkMath.Distance2BetweenPoints(p0, p1)
>> 0.29000000000000042
>> math.sqrt(vtk.vtkMath.Distance2BetweenPoints(p0, p1))
>> 0.53851648071345082
>>
>>
>> On Tue, Jan 14, 2014 at 4:53 PM, Matias Montroull <matimontg at gmail.com>
>> wrote:
>> > Thanks, I will take into account your suggestion.
>> >
>> > Can you run the code with those point samples and tell me what's the
>> > distance you get? I'd like to ensure it works in C++ and then figure out
>> > how
>> > to make it work in ActiViz..
>> >
>> > Thanks,
>> >
>> >
>> > On Tue, Jan 14, 2014 at 8:48 PM, David Gobbi <david.gobbi at gmail.com>
>> > wrote:
>> >>
>> >> Hi Matias,
>> >>
>> >> I don't use Activiz, but something about your code confuses me:
>> >> In C++, Distance2BetweenPoints is overloaded for float and double:
>> >>
>> >>   float Distance2BetweenPoints(const float x[3], const float y[3])
>> >>   double Distance2BetweenPoints(const double x[3], const double y[3])
>> >>
>> >> So how does Activiz know which one of these methods to call?
>> >> If it passes a "double" IntPtr to the float-overloaded method, then the
>> >> result is definitely going to be wrong.
>> >>
>> >> Also: I suggest that you include "Activiz" or "C#" in the subject line
>> >> of all your emails to the list.  That will help to attract the
>> >> attention
>> >> of
>> >> other Activis users, and they are the ones who are most likely to know
>> >> the answers to questions like this one.
>> >>
>> >>   David
>> >>
>> >>
>> >>
>> >>
>> >> On Tue, Jan 14, 2014 at 4:18 PM, Matias Montroull <matimontg at gmail.com>
>> >> wrote:
>> >> > Hi,
>> >> >
>> >> > I'm running this code and I get distance "infinity"... If I change to
>> >> > lower
>> >> > values (1 digit) then it gives a distance..
>> >> > Why?
>> >> >
>> >> >  double[] p0 = new double[] { 10.2, 20.7, 10.4 };
>> >> >    double[] p1 = new double[] { 10.5, 20.5, 10.8};
>> >> >
>> >> >    IntPtr pP0 = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(double)) *
>> >> > 3);
>> >> >    IntPtr pP1 = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(double)) *
>> >> > 3);
>> >> >    Marshal.Copy(p0, 0, pP0, 3);
>> >> >    Marshal.Copy(p1, 0, pP1, 3);
>> >> >
>> >> >    // Find the squared distance between the points.
>> >> >    double squaredDistance = vtkMath.Distance2BetweenPoints(pP0, pP1);
>> >> >
>> >> >    // Take the square root to get the Euclidean distance between the
>> >> > points.
>> >> >    double distance = Math.Sqrt(squaredDistance);
>> >> >
>> >> >    // Output the results.
>> >> >    Console.WriteLine("SquaredDistance = " + squaredDistance);
>> >> >    Console.WriteLine("Distance = " + distance);
>> >> >    Marshal.FreeHGlobal(pP0);
>> >> >    Marshal.FreeHGlobal(pP1);
>> >
>> >
>
>