[vtkusers] positioning a cylinder

[Amy Squillacote]

Hi Mark,

I should have looked more closely at the API for that class. No, you 
can't position using just two points. In fact, the arrow always starts 
at (0, 0, 0) and ends at (1, 0, 0). In order to put the arrow source 
where you want it in space, you'd either have to modify the transform 
associated with the vtkActor rendering the vtkArrowSource, or you could 
pass the output of vtkArrowSource through a vtkTransformFilter before 
passing it to the mapper for rendering.

- Amy

Mark Wyszomierski wrote:
> Hi Amy,
>
> Is there anyway to position vtkArrowSource using just two points?
> Something like:
>
> vtkArrow->SetPointHead(x,y,z);
> vtkArrow->SetPointTail(x,y,z);
>
> Thanks,
> Mark
>
> On 4/2/07, Amy Squillacote <amy.squillacote at kitware.com> wrote:
>> Hi Mark,
>>
>> If what you're wanting is an arrow source class, that already exists in
>> VTK. Take a look at vtkArrowSource:
>> http://www.vtk.org/doc/release/5.0/html/a01163.html.
>>
>> - Amy
>>
>> Mark Wyszomierski wrote:
>> > Thanks Amy, and Marc. I will give it a try. My final goal is to have a
>> > nice arrow class where I can just do:
>> >
>> > Arrow->SetHeadPoint(x,y,z);
>> > Arrow->SetTailPoint(x,y,z);
>> >
>> > Doing this with a cone actor is pretty easy (set the origin and
>> > direction) but for the shaft(cylinder source) it is more complicated.
>> >
>> > Thanks,
>> > Mark
>> >
>> > On 3/31/07, Marc Cotran <marc at cotran.ca> wrote:
>> >> Hi Mark,
>> >>
>> >> I have a 'hard' way of doing what you are asking. The easiest way is
>> >> what Amy proposes, but if you definitely want a cylinder that can 
>> update
>> >> quickly with changes to the endpoints...
>> >>
>> >> - useablePt1 and 2 are classes (Coord) with 3 variables (x, y, z) for
>> >> coordinates. Although we implemented some convenience methods in 
>> Coord,
>> >> you could do it all with vtkMath.
>> >>
>> >> - this->transform corresponds to that of the actor made from the
>> >> cylinderSource
>> >>
>> >> //////////////////////////////
>> >>
>> >>    this->cylinderSource = vtkCylinderSource::New();
>> >>    this->cylinderSource->SetCapping(1);
>> >>    this->cylinderSource->SetResolution(5);
>> >>
>> >>    // find out halfway point
>> >>    Coord halfwayPt(
>> >>        (useablePt1.x() + useablePt2.x()) / 2,
>> >>        (useablePt1.y() + useablePt2.y()) / 2,
>> >>        (useablePt1.z() + useablePt2.z()) / 2);
>> >>
>> >>    double pos[4];
>> >>    double res[4];
>> >>
>> >>    pos[0] = halfwayPt.x();
>> >>    pos[1] = halfwayPt.y();
>> >>    pos[2] = halfwayPt.z();
>> >>    pos[3] = 1;
>> >>
>> >>    this->transform.getTransform()->MultiplyPoint(pos, res);
>> >>
>> >>    // we found the center point
>> >>
>> >>    Coord diff(this->pt2 - this->pt1);
>> >>    Coord normalized(diff.normalize());
>> >>
>> >>    double norm = diff.norm();
>> >>
>> >>    this->cachedActor->SetScale(this->radius, norm, this->radius);
>> >>
>> >>    // get cross product
>> >>    double cross[3];
>> >>    double input[3];
>> >>    double output[3];
>> >>
>> >>    input[0] = 0;
>> >>    input[1] = 1;
>> >>    input[2] = 0;
>> >>
>> >>    output[0] = normalized.x();
>> >>    output[1] = normalized.y();
>> >>    output[2] = normalized.z();
>> >>
>> >>    vtkMath::Cross(input, output, cross);
>> >>
>> >>    // get the angle
>> >>    double angle = HelperClass::getAngle(Coord(0,1,0), Coord(),
>> >> normalized);
>> >>
>> >>    // start with no rotation so they don't accumulate
>> >>    this->cachedActor->SetOrientation(0,0,0);
>> >>
>> >>    this->cachedActor->RotateWXYZ(angle, cross[0], cross[1], 
>> cross[2]);
>> >>
>> >>    this->cachedActor->SetPosition(
>> >>        res[0] / res[3],
>> >>        res[1] / res[3],
>> >>        res[2] / res[3]);
>> >>
>> >> //////////////////////////////
>> >>
>> >> It is quite possible that the code can be optimized (or at least made
>> >> shorter). The only advantage to this method is that you don't have to
>> >> remap the actor when you change one or both of the endpoints. If you
>> >> don't care about updates, I strongly recommend the 
>> lineSource/TubeFilter
>> >> method (it's much simpler!!!)
>> >>
>> >> Marc
>> >>
>> >>
>> >> Mark Wyszomierski wrote:
>> >> > Hi,
>> >> >
>> >> > I have two points in VTK space, is there an easy way to construct a
>> >> > cylinder so that its two endpoints touch the two points? Something
>> >> > like:
>> >> >
>> >> > cylinder->SetEndpoint1(x,y,z);
>> >> > cylinder->SetEndpoint2(x,y,z);
>> >> >
>> >> > Thanks,
>> >> > Mark
>> >> > _______________________________________________
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>>
>> -- 
>> Amy Squillacote
>> Kitware, Inc.
>> 28 Corporate Drive
>> Clifton Park, NY 12065
>> Phone: (518) 371-3971 x106
>>
>>
> _______________________________________________
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-- 
Amy Squillacote
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065
Phone: (518) 371-3971 x106