# points not showing after aplying rotation/translation
**URL:** https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621
**Category:** Support
**Created:** [November 10, 2020, 2:59pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621 "2020-11-10T14:59:12Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 2:59pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/1 "2020-11-10T14:59:12Z")
Hello!
I am trying to rotate some points in space, but when I try plotting them, they do not show. I am not sure why as I put markers in my code before and after the displaying line and it looks like the program executes the line, but for some reason it is not showing…
My code is as follows (similar to [https://lorensen.github.io/VTKExamples/site/Python/Filtering/AppendFilter/](https://lorensen.github.io/VTKExamples/site/Python/Filtering/AppendFilter/))
points = vtk.vtkPoints()
points.InsertNextPoint(…)
points.InsertNextPoint(…)
points.InsertNextPoint(…)
ug = vtk.vtkUnstructuredGrid()
ug.SetPoints(points)
appendFilter = vtk.vtkAppendFilter()
appendFilter.AddInputData(ug)
appendFilter.Update()
mapper = vtk.vtkDataSetMapper()
mapper.SetInputConnection(appendFilter.GetOutputPort())
actor = vtk.vtkActor()
actor.SetMapper(mapper)
actor.GetProperty().SetColor(0.0, 0.0, 1.0)
actor.GetProperty().SetPointSize(10)
ren.AddActor(actor)
I have also tried the following: which it works, but the moment I apply a rotation to them, they disappear and I am not sure why either…
```
points = vtk.vtkPoints()
points.InsertNextPoint(.....)
points.InsertNextPoint(.....)
points.InsertNextPoint(.....)
pointsPolyData = vtk.vtkPolyData()
pointsPolyData.SetPoints(points)
vertexFilter = vtk.vtkVertexGlyphFilter()
vertexFilter.SetInputData(pointsPolyData)
vertexFilter.Update()
mapper= vtk.vtkPolyDataMapper()
mapper.SetInputData(vertexFilter.GetOutput())
actor = vtk.vtkActor()
actor.SetMapper(mapper)
actor.GetProperty().SetColor(0.0, 0.0, 1.0)
actor.GetProperty().SetPointSize(10)
ren.AddActor(actor)
```
For rotating/translating I can apply the vtkTransformPolyDataFilter() and set its input to the vertex/append Filters’s output. Or at least this is how I see what I should do. But the problem is, once I do this, they stop displaying altogether. I tried printing messages during the execution to see if it stops somewhere but as far as that goes, everything goes well. So I am not sure where it stops working.
Any help is appreciated!
-Diana
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 3:19pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/2 "2020-11-10T15:19:45Z")
Hi
You didn’t assign a transform to vtkTransformPolyDataFilter(), so you see nothing in the output.
From the code you posted:
1. No usage of `vtkTransformPolyDataFilter()`.
2. Neither a [`vtkAbstractTransform`](https://vtk.org/doc/nightly/html/classvtkAbstractTransform.html) derived object like [`vtkTransform`](https://vtk.org/doc/nightly/html/classvtkTransform.html) is initialized.
3. Nor is there a call to [`SetTransform`](https://vtk.org/doc/nightly/html/classvtkTransformPolyDataFilter.html#ac7d4167fea7c109577a59a35ec3b9666) on the transformation filter.
Are you sure you did not see any error messages? A lack of `vtkAbstractTransform` should print this [error message](https://github.com/Kitware/VTK/blob/master/Filters/General/vtkTransformPolyDataFilter.cxx#L68) in the logs, since `Transform` is `nullptr`
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 3:25pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/3 "2020-11-10T15:25:45Z")
Yes, sorry. I only posted the first part of the code because in my first code the points would not even show so I thought maybe the problem is there.
This is the rest of the code. (I only posted the part after the calculation of the rotation matrix)
```
rot_obj = vtk.vtkTransform()
rot_obj.Identity()
tr_obj = vtk.vtkMatrix4x4()
for i in range(0,4):
for j in range(0,4):
tr_obj.SetElement(i,j,Total_Transform[i][j])
rot_obj.SetMatrix(tr_obj)
transformFilter=vtk.vtkTransformPolyDataFilter()
transformFilter.SetInputConnection(obj.GetOutputPort())
transformFilter.SetTransform(rot_obj)
transformFilter.Update()
NewMapper = vtk.vtkPolyDataMapper()
NewMapper.SetInputConnection(transformFilter.GetOutputPort())
actorRotated = vtk.vtkActor()
actorRotated.SetMapper(NewMapper)
actorRotated.GetProperty().SetOpacity(0.4)
ren.AddActor(actorRotated)
```
with obj being the object being passed in the function, in my case the vertexFilter or appendFilter.
Yes, I have checked many times and I have no errors…
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 3:37pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/4 "2020-11-10T15:37:46Z")
The pipeline looks alright.
Is anything rendered when you avoid this section of code?
```auto
rot_obj.Identity()
tr_obj = vtk.vtkMatrix4x4()
for i in range(0,4):
for j in range(0,4):
tr_obj.SetElement(i,j,Total_Transform[i][j])
rot_obj.SetMatrix(tr_obj)
```
If you see stuff rendered, then the problem lies in `Total_Transform` and not in the pipeline.
Did you try [this](https://vtk.org/doc/nightly/html/classvtkTransform.html#a9a6bcc6b824fb0a9ee3a9048aa6b262c) instead of directly changing the underlying matrix?
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 3:57pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/5 "2020-11-10T15:57:29Z")
Yes, the render shows my objects with the position before the rotation matrix is applied.
I am not sure why there would be a problem with the transformation matrix because, if I just pass it an actor (random object) it rotates and translates it as it should, but the moment I pass it the points, then they don’t get displayed.
I need to apply this transformation to both points and objects, and it works perfect for objects, but not with points. Is there a difference between a transformation matrix between an object and a point? In my opinion they should be the same, but I might be wrong. I used the Euler-Rodrigues rotation matrix and pre multiplied with the translation matrix and post multiply with the inverse of the translation matrix, so it should be ok.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 4:12pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/6 "2020-11-10T16:12:41Z")
`vtkTransformPolyDataFilter` directly copies over any `Verts` present in its input. So does the generic `vtkTransformFilter`. The transform filters work only on points and do not change the cells.
Is `transformFilter.GetOutput().GetNumberOfPoints()` \> 0 after the update? Also, is `obj.GetOutput().GetNumberOfCells() > 0` after the update?
Edit: fix GetNumberOfPoints()
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 4:19pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/7 "2020-11-10T16:19:52Z")
Just to clarify, the appendFilter does not display anything, and the vertexFilter displays the points. I have wrote wrong before (my apologies), they do display, but not rotated/translated in any way.
For the `transformFilter.GetNumberOfPoints()` I have the following error: `AttributeError: 'vtkmodules.vtkFiltersGeneral.vtkTransformPolyDataF' object has no attribute 'GetNumberOfPoints'`.
And for the `obj.GetOutput().GetNumberOfCells()`, yes both the object and points are \> 0.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 4:21pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/8 "2020-11-10T16:21:32Z")
Edited previous reply to fix error
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 4:22pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/9 "2020-11-10T16:22:54Z")
Yes, they are both \> 0
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 4:24pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/10 "2020-11-10T16:24:27Z")
Can you post the full code with the input point set?
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 4:35pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/11 "2020-11-10T16:35:54Z")
yes of course!
```
ap1 = [np.array([-37.2736, -159.66, -810.009]),
np.array([-32.5138, -164.127, -809.214]),
np.array([-23.6534, -167.229, -808.477])]
ap2 = [np.array([14.8481, -143.84, -831.03]),
np.array([12.861, -146.207, -832.029]),
np.array([17.2145, -139.715, -831.64])]
lig_points = vtk.vtkPoints()
points.InsertNextPoint(ap1[0][0], ap1[0][1], ap1[0][2])
points.InsertNextPoint(ap1[1][0], ap1[1][1], ap1[1][2])
points.InsertNextPoint(ap1[2][0], ap1[2][1], ap1[2][2])
points.InsertNextPoint(ap2[0][0], ap2[0][1], ap2[0][2])
points.InsertNextPoint(ap2[1][0], ap2[1][1], ap2[1][2])
points.InsertNextPoint(ap2[2][0], ap2[2][1], ap2[2][2])
pointsPolyData = vtk.vtkPolyData()
pointsPolyData.SetPoints(points)
vertexFilter = vtk.vtkVertexGlyphFilter()
vertexFilter.SetInputData(pointsPolyData)
vertexFilter.Update()
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputData(vertexFilter.GetOutput())
actor = vtk.vtkActor()
actor.SetMapper(mapper_ligaments)
actor.GetProperty().SetColor(0.0, 0.0, 1.0)
actor.GetProperty().SetPointSize(10)
ren.AddActor(actor)
def rotate(angle, axis, axis_point, obj):
"""Rotate around an arbitrary `axis` passing through `axis_point`."""
axis = axis/np.linalg.norm(axis)
anglerad = np.deg2rad(angle) # transform angle to radians
a = np.cos(anglerad / 2)
b = -axis[0] * np.sin(anglerad / 2)
c = -axis[1] * np.sin(anglerad / 2)
d = -axis[2] * np.sin(anglerad / 2)
size = (a **2 + b** 2 + c **2 + d** 2)**0.5
print("size: ", size)
a, b, c, d = a/size, b/size, c/size, d/size
aa, bb, cc, dd = a * a, b * b, c * c, d * d
bc, ad, ac, ab, bd, cd = b * c, a * d, a * c, a * b, b * d, c * d
Transform_R = np.array(
[
[aa + bb - cc - dd, 2 * (bc + ad), 2 * (bd - ac),0],
[2 * (bc - ad), aa + cc - bb - dd, 2 * (cd + ab),0],
[2 * (bd + ac), 2 * (cd - ab), aa + dd - bb - cc,0],
[0,0,0,1]
]
)
Transform_Neg_Translation = np.array(
[
[1, 0, 0,-axis_point[0]],
[0, 1, 0,-axis_point[1]],
[0, 0, 1,-axis_point[2]],
[0,0,0,1]
]
)
Transform_Pos_Translation = np.array(
[
[1, 0, 0,axis_point[0]],
[0, 1, 0,axis_point[1]],
[0, 0, 1,axis_point[2]],
[0,0,0,1]
]
)
Total_Transform = np.matmul(Transform_Pos_Translation,np.matmul(Transform_R,Transform_Neg_Translation))
rot_obj = vtk.vtkTransform()
rot_obj.Identity()
tr_obj = vtk.vtkMatrix4x4()
for i in range(0,4):
for j in range(0,4):
tr_obj.SetElement(i,j,Total_Transform[i][j])
rot_obj.SetMatrix(tr_obj)
transformFilter=vtk.vtkTransformPolyDataFilter()
transformFilter.SetInputConnection(obj.GetOutputPort())
transformFilter.SetTransform(rot_obj)
transformFilter.Update()
print("Transform get number of points = ", transformFilter.GetOutput().GetNumberOfPoints())
print("Object get number of cells = ", obj.GetOutput().GetNumberOfCells())
NewMapper = vtk.vtkPolyDataMapper()
NewMapper.SetInputConnection(transformFilter.GetOutputPort())
actorRotated = vtk.vtkActor()
actorRotated.SetMapper(NewMapper)
ren.AddActor(actorRotated)
##### data of the line and point the translation is needed
lineStart = [16.8879, -106.476, -782.449]
lineFinish = [-17.827, -92.2757, lineStart[2]]
lineMiddle = [(lineStart[0]+lineFinish[0])/2, (lineStart[1]+lineFinish[1])/2, lineStartPosterior[2]]
line = (np.array(lineFinish) - np.array(lineStart))
rotate(-45, line, lineMiddle, vertexFilter)
```
Also, I forgot to answer your question (sorry!) about me trying [this](https://vtk.org/doc/nightly/html/classvtkTransform.html#a9a6bcc6b824fb0a9ee3a9048aa6b262c). I did try at first with that, but it would rotate about the global coordinate system and not the local one, so that is why I applied the transformation matrix.
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 10, 2020, 4:50pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/12 "2020-11-10T16:50:45Z")
> [@azk](#):
>
> I did try at first with that, but it would rotate about the global coordinate system and not the local one, so that is why I applied the transformation matrix.
Ahh, to fix that, call `rot_obj.PostMultiply()`, by default it is set to `PreMultiply`
Also, you’re not setting up a pipeline here. So changes to `vertexFilter`’s output do not make it to the actor. Use `SetInputConnection` in place of `SetInputData` and `GetOutputPort` in place of `GetOutput` to establish a pipeline.
> mapper.SetInputData(vertexFilter.GetOutput())
---
### Author:  [@azk](https://discourse.vtk.org/u/azk)
#### Post date: [November 10, 2020, 5:38pm UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/13 "2020-11-10T17:38:45Z")
Oh, sorry. I did not realize that!
I did make the changes, but it is the same result…
I still do not understand why the points are showing but then they are not shifting when called in the function, but the object is shifting 🤔
{EDIT} IT FINALLY WORKED!!! It was as you said in the previous answer. I did not set-up the pipeline properly. The reason I was not seeing them shifting was that I did not give a colour and size so the points appeared shifted, but really small and the same colour as my object, so they were basically belnding in perfectly… I only realized this when I turned off the display for my object.
Thank you so much for your help!!! I highly appreciate it!
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [November 11, 2020, 2:41am UTC](https://discourse.vtk.org/t/points-not-showing-after-aplying-rotation-translation/4621/14 "2020-11-11T02:41:07Z")
Glad you got it to work. 👍