# Best way to get notified of camera changes - specifically zoom

**URL:** https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477
**Category:** Support
**Created:** [May 11, 2022, 1:26pm UTC](https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477 "2022-05-11T13:26:44Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![bheld](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/b/8491ac/32.png) [@bheld](https://discourse.vtk.org/u/bheld)
#### Post date: [May 11, 2022, 1:26pm UTC](https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477/1 "2022-05-11T13:26:44Z")

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We have various ways we allow users to zoom in our application such as buttons for fit by window, dynamic zoom that works by depressing mouse button and moving the mouse, zoom by window, etc.

I’m looking for the best way to be notified AFTER such an action is complete. I don’t see events for such changes. I found some reference to camera.onModfied ([bind events to camera](https://discourse.vtk.org/t/bind-events-to-camera/3123)) but this doesn’t actually appear to be supported.

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### Author: ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [May 12, 2022, 10:04pm UTC](https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477/2 "2022-05-12T22:04:21Z")

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You can add an observer to the vtkCameraNode. If you want to be notified after the rendering is completed then you can add an observer to the vtkRenderer.

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### Author: ![bheld](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/b/8491ac/32.png) [@bheld](https://discourse.vtk.org/u/bheld)
#### Post date: [May 12, 2022, 11:52pm UTC](https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477/3 "2022-05-12T23:52:30Z")

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Thanks! Unfortunately there is very little documentation on this class and only one seemingly irrelevant example.

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### Author: ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [May 13, 2022, 12:02am UTC](https://discourse.vtk.org/t/best-way-to-get-notified-of-camera-changes-specifically-zoom/8477/4 "2022-05-13T00:02:25Z")

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You can find all information you need in `vtkCamera.cxx`. Search for `InvokeEvent` to see what events are invoked and when.