# vtkValuePass - Depth Issues

**URL:** https://discourse.vtk.org/t/vtkvaluepass-depth-issues/13071
**Category:** Support
**Tags:** filter, python
**Created:** [January 15, 2024, 8:44am UTC](https://discourse.vtk.org/t/vtkvaluepass-depth-issues/13071 "2024-01-15T08:44:19Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![Kai](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/k/cc9497/32.png) [@Kai](https://discourse.vtk.org/u/Kai)
#### Post date: [January 15, 2024, 8:44am UTC](https://discourse.vtk.org/t/vtkvaluepass-depth-issues/13071/1 "2024-01-15T08:44:19Z")

</div>

Dear VTK Forum,

I am encountering a challenge while working with `vtkValuePass` and have uncertainties regarding the depth value computation. I expect the depth values to behave similarly to the geometric coordinates they correspond to, as they do with a color map. However, objects that should be behind a surface seem to be drawn in front of it.  
I have attached some screenshots for better illustration:

The color map rendering looks like this :  
 ![out1](https://discourse.vtk.org/uploads/default/original/2X/f/fe3944203ae1519934dc7485bef28de868ca06de.png)

The vtkValuePass rendering like this :  
 ![out0](https://discourse.vtk.org/uploads/default/original/2X/f/f1c82110794f4d0f0d2e4c336c7bee5bd8afce3e.jpeg)

The part that looks wrong to me is marked with lightblue :  
 ![Inkedout0_LI](https://discourse.vtk.org/uploads/default/original/2X/0/04de818de2a27c5ab8d13349d5a03fdb152034d3.jpeg)

my code for the value pass is based on the vtk example [RenderScalarToFloatBuffer](https://examples.vtk.org/site/Cxx/Utilities/RenderScalarToFloatBuffer/) , here it is :

```auto
        imgextent = self.image_data.GetExtent()

        renderer = vtk.vtkRenderer()
        renderer.AddActor(self.mesh_actor)
        renderer.SetUseDepthPeeling(True)

        render_window = vtk.vtkRenderWindow()
        render_window.SetMultiSamples(0)
        render_window.SetSize(imgextent[1], imgextent[3])
        render_window.OffScreenRenderingOn()
        render_window.AddRenderer(renderer)

        value_pass = vtk.vtkValuePass()
        value_pass.SetInputArrayToProcess(vtk.VTK_SCALAR_MODE_USE_POINT_FIELD_DATA, "messurment1_dir1")
        value_pass.SetInputComponentToProcess(0)

        render_pass_collection = vtk.vtkRenderPassCollection()
        render_pass_collection.AddItem(value_pass)

        sequence_pass = vtk.vtkSequencePass()
        sequence_pass.SetPasses(render_pass_collection)

        camera_pass = vtk.vtkCameraPass()
        camera_pass.SetDelegatePass(sequence_pass)

        renderer.SetPass(camera_pass)
        renderer.SetActiveCamera(self.renderInterface.GetActiveCamera())
        render_window.Render()

        buffer = value_pass.GetFloatImageDataArray(renderer)

        ext = value_pass.GetFloatImageExtents()
        pointer_hex = int(ext.split('_')[1], 16)
        data_pointer = ctypes.cast(pointer_hex, ctypes.POINTER(ctypes.c_int))
        ext = [data_pointer[0], data_pointer[1], data_pointer[2], data_pointer[3]]
        print(ext)

        width = ext[1]
        height = ext[3]
        f = open('mat.txt', 'w')
        for i in range(width):
            for j in range(height):
                bufferIndex = i*height + j
                value = buffer.GetValue(bufferIndex)
                #print(value)
                f.write(f"{value:9.4e}\n")
            #f.write('\n')
            #print()
        f.close()

        image = vtk.vtkImageData()
        image.SetExtent(ext[0], ext[1], ext[2], ext[3], 0, 0)
        image.GetPointData().SetScalars(buffer)

        lut = vtk.vtkLookupTable()
        lut.SetHueRange(0.6, 0)
        lut.SetSaturationRange(1.0, 0)
        lut.SetValueRange(0.5, 1.0)
        lut.SetTableRange(image.GetScalarRange())

        map_colors = vtk.vtkImageMapToColors()
        map_colors.SetLookupTable(lut)
        map_colors.SetInputDataObject(image)
        map_colors.Update()

        writer = vtk.vtkJPEGWriter()
        writer.SetFileName("out.jpg")
        writer.SetInputData(map_colors.GetOutput())
        writer.Write()

```

I have also tried to use vtkDepthSortPolyData :

```auto
        ...
        self.triangle_polydata = addScalarCellData(self.triangle_polydata, R1, "messurment1_dir1")

        self.depthSortData = vtk.vtkDepthSortPolyData()
        self.depthSortData.SetInputData(self.triangle_polydata)
        self.depthSortData.SetCamera(self.renderInterface.GetActiveCamera())
        self.depthSortData.SortScalarsOn()
        self.depthSortData.SetDirectionToBackToFront()
        #self.depthSortData.SetVector(1, 1, 1)
        self.depthSortData.Update()

        self.mesh_mapper = vtk.vtkPolyDataMapper()
        self.mesh_mapper.SetInputData(self.depthSortData.GetOutput())
        sr = 0.0005
        self.mesh_mapper.SetScalarRange([0., sr])
        self.mesh_mapper.SetLookupTable(self.lut)

        self.mesh_actor = vtk.vtkActor()
        self.mesh_actor.SetMapper(self.mesh_mapper)
        ...

```

Any suggestions would be highly appreciated. 🙂