Automatically Centering Camera on Data After Loading in Python Plugin

ParaView Support
1

I’ve recently updated how I load data in my ParaView using a Python plugin and encountered a camera behavior issue. Initially, the workflow was straightforward:

  1. The user selects the location of the data.
  2. Pressing “Apply” loads the data, and the camera would automatically center on it.

However, after making changes to add more functionality, the workflow now looks like this:

  1. The user selects the location of the data.
  2. Pressing “Apply” loads the metadata.
  3. The user selects a subset of the data to load that was retrieved from the metadata.
  4. Pressing “Apply” loads the selected subset of data.

After implementing these steps, I’ve noticed that the camera no longer automatically centers on the loaded data after the 4th step. Instead, I need to manually use the “Zoom To Data” option to adjust the view.

Is there a way to trigger the “Zoom To Data” functionality within my plugin script, perhaps at the end of RequestData, to ensure the camera automatically centers on the data after it is loaded?

Thanks!

2

Alas, there is not a way to trigger ParaView application-level behavior from a Python plugin, which operates in the VTK layer and is not at all aware of ParaView.

3

Thanks for your reply Cory! I ended up doing something along these lines to manually point the camera in the direction of my object, and it seems to work fine for the data I tried it for:

from paraview.simple import GetActiveCamera

def center_camera_on_object(self, obj):
    # Retrieve bounds of the VTK object
    bounds = [0, 0, 0, 0, 0, 0]
    obj.GetBounds(bounds)
    center_x = (bounds[0] + bounds[1]) / 2
    center_y = (bounds[2] + bounds[3]) / 2
    center_z = (bounds[4] + bounds[5]) / 2

    # Calculate width and height of the object
    size_x = bounds[1] - bounds[0]
    size_z = bounds[5] - bounds[4]
    max_size = max(size_x, size_z)

    # Calculate the required distance to fit the object in the view
    camera = GetActiveCamera()
    camera.SetFocalPoint(center_x, center_y, center_z)
    view_angle = camera.GetViewAngle() * 0.95
    half_angle_rad = math.radians(view_angle / 2)
    distance = (max_size / 2) / math.tan(half_angle_rad)

    # Position the camera at the calculated distance along the Y-axis
    camera.SetPosition(center_x, bounds[3] - distance, center_z)
    camera.SetViewUp(0, 0, 1)

def RequestData(self, request, inInfo, outInfo):
    obj = vtkPartitionedDataSetCollection.GetData(outInfo)
    # load data
    self.center_camera_on_object(obj)
    return 1
4

While that might work in this case where you maybe are using the built-in server mode, it is not good practice to mix VTK-level and ParaView-scripting level code. We specifically warn against doing this in the ParaView documentation: 5. Programmable Filter — ParaView Documentation 5.12.0 documentation (see the Common Errors section, which apply also to Python algorithm-based plugins).