# Rotation of camera in 3D view without random tilting
**URL:** https://discourse.slicer.org/t/rotation-of-camera-in-3d-view-without-random-tilting/31842
**Category:** Development
**Created:** [September 22, 2023, 10:20am UTC](https://discourse.slicer.org/t/rotation-of-camera-in-3d-view-without-random-tilting/31842 "2023-09-22T10:20:46Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@moraleda](https://discourse.slicer.org/u/moraleda)
#### Post date: [September 22, 2023, 10:20am UTC](https://discourse.slicer.org/t/rotation-of-camera-in-3d-view-without-random-tilting/31842/1 "2023-09-22T10:20:46Z")
Hi everyone,
as some of you might feel as I do that the camera in 3D view tilts when rotating, I have rewritten the code in `Slicer/Libs/MRML/DisplayableManger/vtkMRMLCameraWidget.cxx` in `vtkMRMLCameraWidget::ProcessRotate` as the following and then built my own Slicer.
```auto
//----------------------------------------------------------------------------
bool vtkMRMLCameraWidget::ProcessRotate(vtkMRMLInteractionEventData* eventData)
{
if (!this->Renderer || !eventData)
{
return false;
}
const int* eventPosition = eventData->GetDisplayPosition();
int dx = eventPosition[0] - this->PreviousEventPosition[0];
int dy = eventPosition[1] - this->PreviousEventPosition[1];
if (dx == 0 && dy == 0)
{
return true;
}
const int *size = this->Renderer->GetRenderWindow()->GetSize();
double delta_elevation = -20.0 / size[1];
double delta_azimuth = -20.0 / size[0];
double rxf = (double)dx * delta_azimuth * this->MotionFactor;
double ryf = (double)dy * delta_elevation * this->MotionFactor;
vtkCamera* camera = this->GetCamera();
if (!camera)
{
return false;
}
bool wasCameraNodeModified = this->CameraModifyStart();
if (this->CameraTiltLocked == true)
{
camera->Azimuth(rxf);
}
else
{
const double* cameraPosition = camera->GetPosition();
const double* cameraFocalPoint = camera->GetFocalPoint();
const double* cameraViewUp = camera->GetViewUp();
bool upside_down = cameraViewUp[2] < 0;
double upside_down_factor = upside_down ? -1.0 : 1.0;
double P[3] = {
cameraPosition[0] - cameraFocalPoint[0],
cameraPosition[1] - cameraFocalPoint[1],
cameraPosition[2] - cameraFocalPoint[2]
};
double H = sqrt(P[0] * P[0] + P[1] * P[1]);
double elev = atan2(P[2], H);
double sin_elev = sin(elev);
double azi;
if (abs(sin_elev) < 0.8) {
azi = atan2(P[1], P[0]);
} else {
if (sin_elev < -0.8) {
azi = atan2(upside_down_factor * cameraViewUp[1], upside_down_factor * cameraViewUp[0]);
} else {
azi = atan2(-upside_down_factor * cameraViewUp[1], -upside_down_factor * cameraViewUp[0]);
}
}
double D = sqrt(P[0] * P[0] + P[1] * P[1] + P[2] * P[2]);
double azi_new = azi + rxf / 60.0;
double elev_new = elev + upside_down_factor * ryf / 60.0;
double Hnew = D * cos(elev_new);
double Pnew[3] = {
Hnew * cos(azi_new),
Hnew * sin(azi_new),
D * sin(elev_new)
};
double up_z = upside_down_factor * cos(elev_new);
double up_h = upside_down_factor * sin(elev_new);
double up_new[3] = {
-up_h * cos(azi_new),
-up_h * sin(azi_new),
up_z
};
double new_pos[3] = {
cameraFocalPoint[0] + Pnew[0],
cameraFocalPoint[1] + Pnew[1],
cameraFocalPoint[2] + Pnew[2]
};
camera->SetViewUp(up_new);
camera->SetPosition(new_pos);
}
camera->OrthogonalizeViewUp();
this->CameraModifyEnd(wasCameraNodeModified, true, true);
this->PreviousEventPosition[0] = eventPosition[0];
this->PreviousEventPosition[1] = eventPosition[1];
return true;
}
```
I particularly changed the code after
```auto
if (this->CameraTiltLocked == true)
{
camera->Azimuth(rxf);
}
else
{ # changes are made here
```
I hope you will find it usefull as well 🙂
The code was rewritten to C++ based on this py-file:
[https://github.com/RubendeBruin/DAVE/blob/d0dec40c9a2e9416f31edabfeaf1f769fb6eca51/src/DAVE/visual\_helpers/vtkBlenderLikeInteractionStyle.py#L4](https://github.com/RubendeBruin/DAVE/blob/d0dec40c9a2e9416f31edabfeaf1f769fb6eca51/src/DAVE/visual_helpers/vtkBlenderLikeInteractionStyle.py#L4)
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [September 22, 2023, 2:33pm UTC](https://discourse.slicer.org/t/rotation-of-camera-in-3d-view-without-random-tilting/31842/2 "2023-09-22T14:33:13Z")
Thank you for raising this and providing an example of an additional method for constraining camera rotation in the 3D view.
The camera’s view-up direction may indeed unintentionally spin as the camera is rotated around. Although it is quite easy to fix it by either moving the mouse in a circle or spinning the view using Ctrl + Click-and-drag, it is even better if it can be avoided in the first place. The “Tilt lock” option was added for exactly this reason, but it may be a bit too restrictive to not let users to change the view-up direction at all.
Your code snippet is nice in that it allows tilting but not spinning of the view-up direction, this allows some more freedom than completely locking the view-up direction, but more controlled than letting anything rotated anywhere. However, the current impmlementation you shared has the patient IS axis hardcoded to be the view-up direction. This is great if you want the patient S direction to point upwards, but extremely annoying when you want to make some other axis to point upwards - for example to show a lateral view of the patient (as lying on the CT table). This view orientation is impossible to achieve with code you proposed:
We cannot remove the current free motion and probably want to keep the “tilt lock” option as well, but we could add a third “Spin lock” option. It would do almost what you implemented, but instead of always keeping the patient IS axis as view-up, it would keep an arbitrarily chosen direction as view-up. The “arbitrarily chosen direction” would actually be the view-up direction at the time when “Spin lock” is activated.
If you can make this improvement we would be happy to add this “Spin lock” option to Slicer core.
---
### Author:  [@moraleda](https://discourse.slicer.org/u/moraleda)
#### Post date: [September 22, 2023, 5:27pm UTC](https://discourse.slicer.org/t/rotation-of-camera-in-3d-view-without-random-tilting/31842/3 "2023-09-22T17:27:36Z")
Hi @lassoan,
yes, you are right that my code is somewhat restricted. I had not noticed before the issue that you addressed. I will try to add the feature you said.
Thanks!