# how to 3d volume render numpy array
**URL:** https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261
**Category:** Support
**Created:** [September 21, 2020, 8:04am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261 "2020-09-21T08:04:51Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@YolkandWhite](https://discourse.vtk.org/u/YolkandWhite)
#### Post date: [September 21, 2020, 8:04am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/1 "2020-09-21T08:04:51Z")
I’m trying to volume render an 3d numpy array with vtk python.
I used to render it by getting the stack of images,
but I’m trying to volume render with an 3d numpy array instead of stack of images.
this picture below is my first try and it doesn’t look good.
```
data = box # box is 3d array
imdata = vtk.vtkImageData()
depthArray = numpy_support.numpy_to_vtk(data.ravel(), deep=True, array_type=vtk.VTK_DOUBLE)
imdata.GetPointData().SetScalars(depthArray)
volumeMapper.SetInputData(imdata)
```
I think these are something that needs to be fixed.
My input is not Image, It’s an 3d array.
What should I fix it?
---
### Author:  [@Charles\_Gueunet](https://discourse.vtk.org/u/Charles_Gueunet)
#### Post date: [September 21, 2020, 10:02am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/2 "2020-09-21T10:02:02Z")
I am not famiiar with `numpy_support` so someone else may help you better to fix the issue on your code.
However, to pass a numpy array as point data (in 0-copy), I use the following snippet in VTK python:
```auto
floatData = np.array([0, 1, 0.5], 'f') # my numpy array
floatArray = vtk.vtkFloatArray() # the VTK array
floatArray.SetName("My array")
floatArray.SetNumberOfComponents(1)
floatArray.SetArray(floatData, 3, False) # False because we do not take the ownership
mydata.GetPointData().SetScalars(floatArray); # give the array to the dataset
```
Hope that helps
---
### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [September 21, 2020, 7:07pm UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/3 "2020-09-21T19:07:57Z")
You have forgot to set up appropriate transfer functions. Specifying scalar opacity transfer function is a minimum, for nicer rendering you probably also want color transfer function. Check out VTK examples (like [this](https://lorensen.github.io/VTKExamples/site/Python/VolumeRendering/SimpleRayCast/)) and documentation for details. Determining transfer functions using Python scripting is tedious, so I would recommend Paraview’s transfer function editor for general engineering visualization and 3D Slicer’s volume rendering module for medical image visualization.
---
### Author:  [@YolkandWhite](https://discourse.vtk.org/u/YolkandWhite)
#### Post date: [September 22, 2020, 1:08am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/4 "2020-09-22T01:08:58Z")
Yes I did set the color transfer function and opacity.
I haven’t show the whole code yet.
below is my whole code.
```
from vtk.util import numpy_support
import vtk
import numpy as np
box = []
for i in range(1536):
loader = np.loadtxt("/Users/nyh/Documents/RP_lab/XRF/nparray/"+str(i+1)+".npy")
box.append(loader)
box = np.stack(box)
data = box
imdata = vtk.vtkImageData()
depthArray = numpy_support.numpy_to_vtk(data.ravel(), deep=True, array_type=vtk.VTK_DOUBLE)
imdata.SetDimensions(data.shape)
imdata.SetSpacing([1,1,1])
imdata.SetOrigin([0,0,0])
imdata.GetPointData().SetScalars(depthArray)
colorFunc = vtk.vtkColorTransferFunction()
# colorFunc.AddRGBPoint(1, 1, 0.0, 0.0) # Red
colorFunc.AddRGBPoint(2, 0.0, 1, 0.0) # Green
opacity = vtk.vtkPiecewiseFunction()
volumeProperty = vtk.vtkVolumeProperty()
volumeProperty.SetColor(colorFunc)
volumeProperty.SetScalarOpacity(opacity)
volumeProperty.SetInterpolationTypeToLinear()
volumeProperty.SetIndependentComponents(2)
volumeMapper = vtk.vtkOpenGLGPUVolumeRayCastMapper()
volumeMapper.SetInputData(imdata)
volumeMapper.SetBlendModeToMaximumIntensity()
volume = vtk.vtkVolume()
volume.SetMapper(volumeMapper)
volume.SetProperty(volumeProperty)
ren = vtk.vtkRenderer()
ren.AddVolume(volume)
ren.SetBackground(0,0,0)
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
renWin.SetSize(900, 900)
interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(renWin)
interactor.Initialize()
renWin.Render()
interactor.Start()
```
When I visualize the array data with pyvista, it looks like this.
every slice of array has a circular data inside.
but I don’t see any circles with VTK.
---
### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [September 22, 2020, 5:16am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/5 "2020-09-22T05:16:18Z")
It looks like your scalar opacity transfer function is incorrect. It is easier to learn how to create good transfer functions by using a GUI (Paraview, 3D Slicer, etc).
---
### Author:  [@xavArtley](https://discourse.vtk.org/u/xavArtley)
#### Post date: [September 25, 2020, 5:21am UTC](https://discourse.vtk.org/t/how-to-3d-volume-render-numpy-array/4261/6 "2020-09-25T05:21:09Z")
Did you take care about order c or fortran?
Try data.ravel(order=‘F’)