Re: Color PolyData based on VolumeData

Thanks a lot!
The solution from Andaharoo was what I was looking for.

pon., 3 gru 2018 o 07:50 Andras Lasso <[email protected]> napisał(a):

> You can copy voxel values from a volume to a polydata using vtkProbeFilter.
>
> However, this won't help you if you obtained your polydata using a
> vtkContourFilter, because the contour filter generates isosurface, which
> means all extracted points have the same intensity value in the input
> volume. No matter what transfer function you apply, you'll always end up
> with a solid colored surface.
>
> It is a common desire to replace volume rendering by displaying a colored
> surface, but this is not feasible (
> https://discourse.slicer.org/t/save-volume-rendering-as-stl-file/524/20).
>
> If your goal is 3D printing then you may use voxel printing technique,
> which allows printing directly from volume rendering, without segmenting
> any surfaces (
> https://discourse.slicer.org/t/printing-volume-renderings-in-plastic/3017
> ).
>
> If your goal is volume-rendering-like display (for example, you want to
> show "volume rendering" in Unity) then you need to use an actual volume
> renderer.
>
> Andras
>
>
> -----Original Message-----
> From: vtkusers <[email protected]> On Behalf Of
> Andaharoo
> Sent: Sunday, December 2, 2018 11:27 PM
> To: [email protected]
> Subject: Re: [vtkusers] Color PolyData based on VolumeData
>
> So, if I understand right, you want to color the scalar/whatever field
> onto the poly? Just provide vtkPolyData with scalars and set the polyData's
> mapper scalar visibility to on.
>
> If you give it 1 component scalars you can give the mapper a color
> function to map them. If you give it 3 component uchar it should just
> display them as color (as long as scalar visibility is on). Like so:
>
>
> // Create the scalars array
> vtkDoubleArray* scalars = vtkDoubleArray::New();
> scalars->SetName("Scalars");
> // For every point in the poly
> for (vtkIdType i = 0; i < outputPoly->GetNumberOfPoints(); i++) {
>         double pt[3];
>         outputPoly->GetPoint(i, pt);
>
>         scalars->InsertTuple1(i, trilinearSamplePoint(inputImage, pt[0],
> pt[1], pt[2], 1, 0)); } // Add the scalar data to the poly data
> outputPoly->GetPointData()->AddArray(scalars);
> outputPoly->GetPointData()->SetActiveScalars("Scalars");
>
>
> This just goes through all the points in the polygon and gets the color
> from the image. Getting the color at a point in an image can be done by
> simply using the nearest color from the image (nearest neighbor) or better
> would be to use trilinear interpolation of the 8 nearest colors which I
> used in my example. Also note my code expects float image input:
> static const int calcIndex(int x, int y, int z, int width, int height) {
> return x + width * (y + height * z); }
>
> static float trilinearSamplePoint(vtkImageData* imageData, float x, float
> y, float z, int numComps, int comp) {
>         float* imagePtr =
> static_cast<float*>(imageData->GetScalarPointer());
>         double* spacing = imageData->GetSpacing();
>         double* origin = imageData->GetOrigin();
>         int* dim = imageData->GetDimensions();
>
>         // We assume point x, y, z is in the image
>         int xi = (x - origin[0]) / spacing[0];
>         int yi = (y - origin[1]) / spacing[1];
>         int zi = (z - origin[2]) / spacing[2];
>
>         // Get the intensities at the 8 nearest neighbors
>         float i000 = imagePtr[calcIndex(xi, yi, zi, dim[0], dim[1]) *
> numComps + comp];
>         float i100 = imagePtr[calcIndex(xi + 1, yi, zi, dim[0], dim[1]) *
> numComps
> + comp];
>         float i110 = imagePtr[calcIndex(xi + 1, yi + 1, zi, dim[0], dim[1]
> * numComps + comp)];
>         float i010 = imagePtr[calcIndex(xi, yi + 1, zi, dim[0], dim[1]) *
> numComps
> + comp];
>
>         float i001 = imagePtr[calcIndex(xi, yi, zi + 1, dim[0], dim[1]) *
> numComps
> + comp];
>         float i101 = imagePtr[calcIndex(xi + 1, yi, zi + 1, dim[0],
> dim[1]) * numComps + comp];
>         float i111 = imagePtr[calcIndex(xi + 1, yi + 1, zi + 1, dim[0],
> dim[1]) * numComps + comp];
>         float i011 = imagePtr[calcIndex(xi, yi + 1, zi + 1, dim[0],
> dim[1]) * numComps + comp];
>
>         // Get the fractional/unit distance from nearest neighbor 000
>         float rx = xi * spacing[0] + origin[0]; // Position of node
>         rx = (x - rx) / spacing[0]; // (Node - actual point position) /
> voxel width
>         float ry = yi * spacing[1] + origin[1];
>         ry = (y - ry) / spacing[1];
>         float rz = zi * spacing[2] + origin[2];
>         rz = (z - rz) / spacing[2];
>
>         // Now we do the trilinear interpolation
>         float ax = i000 + (i100 - i000) * rx;
>         float bx = i010 + (i110 - i010) * rx;
>         float cy = ax + (bx - ax) * ry;
>
>         float dx = i001 + (i101 - i001) * rx;
>         float ex = i011 + (i111 - i011) * rx;
>         float fy = dx + (ex - dx) * ry;
>
>         float gz = cy + (fy - cy) * rz;
>         return gz;
> }
>
>
>
>
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