# Centerline projection after registration

**URL:** <https://discourse.slicer.org/t/centerline-projection-after-registration/39740>\
**Category:** Development\
**Created:** [October 17, 2024, 5:18am UTC](https://discourse.slicer.org/t/centerline-projection-after-registration/39740 "2024-10-17T05:18:22Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![fqzhice](https://avatars.discourse-cdn.com/v4/letter/f/7bcc69/32.png) [@fqzhice](https://discourse.slicer.org/u/fqzhice)\
**Post date:** [October 17, 2024, 5:18am UTC](https://discourse.slicer.org/t/centerline-projection-after-registration/39740/1 "2024-10-17T05:18:22Z")

</div>

I extract vessel centerline by vmtk with type vtkMRMLModelNode.

Then i want get ijk coord for centerline projection after rigistration.

```auto
line = [] #line projection
centerlineNode = slicer.util.getNode('Centerlinemodel')  
mesh = centerlineNode.GetMesh()  
points = mesh.GetPoints()  
for id in range(points.GetNumberOfPoints()):  
point_Ras = points.GetPoint(id)  
point_ijk = self.ras2ijk(point_Ras, vessel_src_Node)  
point_kji = [point_ijk[2],point_ijk[1],point_ijk[0]]  
print('index:',point_kji) # image coordinate position
...

    def ras2ijk(self, point_Ras, volumeNode):
        transformRasToVolumeRas = vtk.vtkGeneralTransform(
        slicer.vtkMRMLTransformNode.GetTransformBetweenNodes( volumeNode.GetParentTransformNode(),None,
                                                             transformRasToVolumeRas)
        point_VolumeRas = transformRasToVolumeRas.TransformPoint(point_Ras)
        volumeRasToIjk = vtk.vtkMatrix4x4()
        volumeNode.GetRASToIJKMatrix(volumeRasToIjk)
        point_ijk = [0, 0, 0, 1]
        volumeRasToIjk.MultiplyPoint(np.append(point_VolumeRas, 1.0), point_ijk)
        point_ijk = [int(round(c)) for c in point_ijk[0:3]]
       return point_ijk

```

Is that conversion right? point\_kji get some invalid value such as minus value or value out of range.