[vtkusers] Access to Cells in VTK.js

[Sebastien Jourdain]

point picker or cell picker won't give you the same ijk since one will be
the point ijk vs the cell one.

On Fri, Jan 18, 2019 at 11:42 AM Andrzej Marciniak <
marciniak.andrzej.zg at gmail.com> wrote:

> Hi Sebastien,
>
> Thank you for the tip - it works for me. Now, I have only a problem with
> precision in finding IJK.
> Should I better use vtkPicker or vtkMappers to get IJK position of selected
> voxel? I have made a simple experiment with both ways to calculate IJK and
> I
> got different results.
>
>  renderWindow.getInteractor().onRightButtonPress((callData) => {
>             if (renderer !== callData.pokedRenderer) {
>                 return;
>             }
>             const pos = callData.position;
>             const point = [pos.x, pos.y, 0.0];
>             picker.pick(point, renderer);
>             const worldPos = picker.getPickedPositions()[0];
> //I have only one Actor in renderer but 3 mappers set on different planes
>             let slices = null;
>             try {
>                 slices = mappers.map((el) => {
>                     return el.getSliceAtPosition(worldPos) // this is how I
> get I,J,K with ImageMapper API
>                 });
>             }
>             catch (err) {  alert("You cannot pick a point outside MRI
> volume");
>                 return;
>             }
>             const pointIndex = slices[0] + slices[1] * dims[0] + slices[2]
> *
> dims[0] * dims[1];
>             const pointIndex2 = picker.getCellIJK()[0]
>                                + picker.getCellIJK()[1] * dims[0]
>                                + picker.getCellIJK()[2] * dims[0] *
> dims[1];
>             if (pointIndex===pointIndex2)
> inputData.getPointData().getScalars().getData()[pointIndex]=1983;
>
>             else {
>
> inputData.getPointData().getScalars().getData()[pointIndex]=1700;
>
> inputData.getPointData().getScalars().getData()[pointIndex2]
> = 1500;
>             }
>         });
> <http://vtk.1045678.n5.nabble.com/file/t342677/pickerProblem.png>
> As a result I have different voxels marked (please see image).  White voxel
> is when they agree, light- and dark-grey when they don't. The results are
> different when the selected point on canvas is close to the border of voxel
> (points 1 and 3).
> Which way is better?  Can be direction of the vtkDataImage problem here
> (its
> not aligned with xyz coordinates)?
> Thank you again
> Andrzej
>
>
>
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