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    Hello Cory,<br>
    I was able to use your suggestion and got some code to work, as
    follows:<br>
    <br>
        virtual void Execute(vtkObject *caller, unsigned long, void*)<br>
        {<br>
            static int callCount = 0;<br>
            static double lastAngle = 0;<br>
            static double lastVec[3] = {0,0,0};<br>
            vtkSmartPointer<vtkTransform> t =   
    vtkSmartPointer<vtkTransform>::New();<br>
            static vtkSmartPointer<vtkTransform> lastTransform =
    vtkSmartPointer<vtkTransform>::New();<br>
            vtkBoxWidget *widget =
    reinterpret_cast<vtkBoxWidget*>(caller);<br>
            widget->GetTransform(t);<br>
    <br>
            double* wxyz = t->GetOrientationWXYZ();<br>
            double* lastWXYZ = lastTransform->GetOrientationWXYZ();<br>
    <br>
            if(anActor)<br>
            {<br>
                cout<<"CallCount:
    "<<callCount<<"Current Angle "<<wxyz[0]<<"
    Effective angle:"<< wxyz[0] - lastAngle<<endl;<br>
    <br>
                //Transform 'back'<br>
                anActor->RotateWXYZ(-lastAngle, lastWXYZ[1],
    lastWXYZ[2], lastWXYZ[3]);<br>
                anActor->RotateWXYZ(wxyz[0], wxyz[1], wxyz[2],
    wxyz[3]);<br>
            }<br>
    <br>
            //Save transform data<br>
            lastAngle = wxyz[0] ;<br>
            lastVec[0] =wxyz[1];<br>
            lastVec[1] =wxyz[2];<br>
            lastVec[2] =wxyz[3];<br>
    <br>
            lastTransform = t;<br>
            callCount++;<br>
        }<br>
    <br>
    In the above code, two transformations of the actor are done, in
    order to follow the orientation of the widget. 1) to rotate the
    actor to its initial position, and 2), applying current
    transformation.<br>
    <br>
    Although the above code works, is there a way to get the
    'incremental' transform somehow? I'm a novice about these things so
    sorry if asking something obvious...<br>
    <br>
    tk<br>
    <br>
    <br>
    <div class="moz-cite-prefix">On 8/6/2015 7:40 AM, Cory Quammen
      wrote:<br>
    </div>
    <blockquote
cite="mid:CAB5Fpx7g=JksY4oYX50S8-W2LndGX=KrrHs7xnQ_2uDLW21CsA@mail.gmail.com"
      type="cite">
      <div dir="ltr">TK,
        <div><br>
        </div>
        <div>You can get the orientation in angle-axis representation
          with</div>
        <div><br>
        </div>
        <div>double wxyz[4];</div>
        <div>t->GetOrientationWXYZ(wxyz);</div>
        <div><br>
        </div>
        <div>From the docs [1]:</div>
        <div><br>
        </div>
        <div><span
style="color:rgb(0,0,0);font-family:Roboto,sans-serif;font-size:14px;line-height:22px">The
            angle (w) is in degrees and the axis (xyz) is a unit vector.</span><br>
        </div>
        <div><br>
        </div>
        <div>You should be able to apply this rotation to your molecule
          model's RotateAboutVector function.</div>
        <div><br>
        </div>
        <div>HTH,</div>
        <div>Cory</div>
        <div><span
style="color:rgb(0,0,0);font-family:Roboto,sans-serif;font-size:14px;line-height:22px"><br>
          </span></div>
        <div><span
style="color:rgb(0,0,0);font-family:Roboto,sans-serif;font-size:14px;line-height:22px">[1] </span><font
            color="#000000" face="Roboto, sans-serif"><span
              style="font-size:14px;line-height:22px"><a
                moz-do-not-send="true"
href="http://www.vtk.org/doc/nightly/html/classvtkTransform.html#aa8244cbab95a2dbb20e94af6e7f16b7f"><a class="moz-txt-link-freetext" href="http://www.vtk.org/doc/nightly/html/classvtkTransform.html#aa8244cbab95a2dbb20e94af6e7f16b7f">http://www.vtk.org/doc/nightly/html/classvtkTransform.html#aa8244cbab95a2dbb20e94af6e7f16b7f</a></a></span></font></div>
        <div><br>
        </div>
      </div>
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Wed, Aug 5, 2015 at 8:54 PM, Totte
          Karlsson <span dir="ltr"><<a moz-do-not-send="true"
              href="mailto:totte@dunescientific.com" target="_blank">totte@dunescientific.com</a>></span>
          wrote:<br>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello,<br>
            I'm using vtk to visualize 3D models of molecules.<br>
            The actual molecular model is decoupled from vtk code, and
            visualization is implemented using a model-view kind of
            design.<br>
            <br>
            Currently I have the following challenge. If a user wants to
            manipulate the absolute orientation of the molecule, it is
            done by manipulating the underlying model using rotation
            functions, like RotateX, RotateY, RotateAboutVector, and
            translation functions TranslateX, Y etc.<br>
            <br>
            For now 3D rotations are simply done using two scrollbars,
            one horizontal and one vertical, causing the underlying
            model being rotated about the vtk viewUP vector and the vtk
            cameraPlane normal respectively.  This works fine, but is
            not so intuitive for the user.<br>
            <br>
            Instead I believe allowing interaction with something like a
            box widget that encapsulates the molecule view, (with
            disabled handles), would be better.<br>
            <br>
            The challenge is how to figure out how to capture the
            boxwidgets orientation in a callback, and using this
            information in order to manipulate the underlying molecular
            model.<br>
            <br>
            For example, a boxwidget callback (from boxwidget example at
            <a moz-do-not-send="true"
              href="http://www.vtk.org/Wiki/VTK/Examples/Cxx/Widgets/BoxWidget"
              rel="noreferrer" target="_blank">http://www.vtk.org/Wiki/VTK/Examples/Cxx/Widgets/BoxWidget</a>):<br>
            <br>
            class vtkMyCallback : public vtkCommand<br>
            {<br>
                public:<br>
                    static vtkMyCallback *New()       {           
            return new vtkMyCallback;    }<br>
            <br>
                virtual void Execute(vtkObject *caller, unsigned long,
            void*)<br>
                {<br>
                    vtkSmartPointer<vtkTransform> t =
            vtkSmartPointer<vtkTransform>::New();<br>
                    vtkBoxWidget *widget =
            reinterpret_cast<vtkBoxWidget*>(caller);<br>
                    widget->GetTransform(t);<br>
            <br>
                    double* angles?? = t->GetOrientation();<br>
                    if(aMoleculeModel)<br>
                    {<br>
                        //Use some secret(!) code to manipulate
            orientation of a molecule to 'rotate' it together with the
            boxWidget<br>
                        aMoleculeModel->RotateZ(??);<br>
                        aMoleculeModel->RotateY(??);<br>
                        aMoleculeModel->RotateZ(??);<br>
                    }<br>
                }<br>
                Molecule* aMoleculeModel;<br>
            <br>
            Anyone seeing how to do this or have some pointers?<br>
            <br>
            Cheers,<br>
            tk<br>
            <br>
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        </div>
        <br>
        <br clear="all">
        <div><br>
        </div>
        -- <br>
        <div class="gmail_signature">Cory Quammen<br>
          R&D Engineer<br>
          Kitware, Inc.</div>
      </div>
    </blockquote>
    <br>
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              <div style="font-size:10px;color:#666666"> Totte Karlsson:
                <a moz-do-not-send="true"
                  href="mailto:totte@dunescientific.com" target="_blank">totte@dunescientific.com</a>
                or <a moz-do-not-send="true"
                  href="tel:%20425%20%20780-9648" value="+14257809648"
                  target="_blank">(425) 780-9648</a><br>
                <a moz-do-not-send="true"
                  href="http://www.dunescientific.com/" target="_blank">http://www.dunescientific.com/</a>
                <br>
                © 2015 Dune Scientific, LLC. All rights reserved. </div>
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