### Author:  [@cnkhanh](https://discourse.itk.org/u/cnkhanh)
#### Post date: [September 20, 2022, 5:21am UTC](https://discourse.itk.org/t/how-to-fix-itkmatrixd33-object-does-not-support-indexing-itk-binarymask3dmeshsource/5347/1 "2022-09-20T05:21:31Z")
The below is the code in C++
> typename ImageType::DirectionType imageDirection=inputImage-\>GetDirection();
> //… mesh generated using itk::BinaryMask3DMeshSource
> typename MeshType::Pointer mesh = meshSource-\>GetOutput();
> typename PointsContainer::Pointer points = mesh-\>GetPoints();
> PointsContainer::Iterator PointIterator = points-\>Begin();
>
> while(PointIterator !=points-\>End() )
> {
> PointType p=(PointIterator).Value();
> PointType p2;
> p2.Fill(0.0);
>
> ```
> for(unsigned int iPointDim=0; iPointDim< Dimension; iPointDim++)
> {
> for(unsigned int iDim=0; iDim {
> p2[iPointDim] += imageDirection[iPointDim][iDim]*p[iDim];
> }
> }
>
> ```
>
> }
* * *
I tried to do the same thing in Python
1. I read the (.hdr) image from file, getDirection() of this image.
2. I generated a mesh using itk.BinaryMask3DMeshSource
3. The while loop (from C++), I wrote as below:
```auto
for i in range(points.Size()):
p = points.ElementAt(i)
PixelType = itk.F
p2 = itk.Point[PixelType, Dimension]()
p2.Fill(0.0)
for iPointDim in range(0, Dimension):
for iDim in range(0, Dimension):
p2[iPointDim] += imageDirection_itk[iPointDim][iDim]*p[iDim];
```
==\> But I received an error (TypeError: ‘itkMatrixD33’ object does not support indexing) at line “p2[iPointDim] += imageDirection\_itk[iPointDim][iDim]\*p[iDim];”
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [September 20, 2022, 11:59am UTC](https://discourse.itk.org/t/how-to-fix-itkmatrixd33-object-does-not-support-indexing-itk-binarymask3dmeshsource/5347/2 "2022-09-20T11:59:12Z")
Try `imageDirection_itk(iPointDim, iDim)` and `imageDirection_itk.GetElement(iPointDim, iDim)`. Take a look at [this post](https://discourse.itk.org/t/set-image-direction-from-numpy-array/844/11) and the rest of that thread.
---
### Author:  [@cnkhanh](https://discourse.itk.org/u/cnkhanh)
#### Post date: [September 21, 2022, 12:38am UTC](https://discourse.itk.org/t/how-to-fix-itkmatrixd33-object-does-not-support-indexing-itk-binarymask3dmeshsource/5347/3 "2022-09-21T00:38:31Z")
Thank you. It works.
The next thing in C++ is,
```auto
(PointIterator).Value()=p2;
PointIterator++;
// End while PointIterator
```
I though that this line “(PointIterator).Value()=p2” used to set value for the current point in while loop.
And I try to do like this in Python by the following
```auto
points.ElementAt(i) = p2
```
And I received the error “SyntaxError: can’t assign to function call”
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [September 21, 2022, 1:27am UTC](https://discourse.itk.org/t/how-to-fix-itkmatrixd33-object-does-not-support-indexing-itk-binarymask3dmeshsource/5347/4 "2022-09-21T01:27:52Z")
Have you tried `points.SetElement(i, p2)`?
@Pranjal_Sahu might be more up to date on syntax for this.
---
### Author:  [@cnkhanh](https://discourse.itk.org/u/cnkhanh)
#### Post date: [September 21, 2022, 1:53am UTC](https://discourse.itk.org/t/how-to-fix-itkmatrixd33-object-does-not-support-indexing-itk-binarymask3dmeshsource/5347/5 "2022-09-21T01:53:39Z")
> [@dzenanz](#):
>
> SetElement(i, p2)
Yes, It work. Thank you so much