# Building an annotation software using VTK's interactor - issue with coordinate skipping

**URL:** https://discourse.vtk.org/t/building-an-annotation-software-using-vtks-interactor-issue-with-coordinate-skipping/12794
**Category:** Support
**Tags:** python, code
**Created:** [November 27, 2023, 10:50am UTC](https://discourse.vtk.org/t/building-an-annotation-software-using-vtks-interactor-issue-with-coordinate-skipping/12794 "2023-11-27T10:50:36Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![zemmyang](https://discourse.vtk.org/user_avatar/discourse.vtk.org/zemmyang/32/8068_2.png) [@zemmyang](https://discourse.vtk.org/u/zemmyang)
#### Post date: [November 27, 2023, 10:50am UTC](https://discourse.vtk.org/t/building-an-annotation-software-using-vtks-interactor-issue-with-coordinate-skipping/12794/1 "2023-11-27T10:50:36Z")

</div>

Here’s what I’m talking about:

![Animation](https://discourse.vtk.org/uploads/default/original/2X/1/10caeacc29bcc1f9efb837c1945e4be585bb8ed1.gif)

The third one is potentially very problematic - what I do after the points have been dragged is to connect the coordinates and use that to create a region of interest. If the coordinates don’t save correctly (and they don’t if the visualization looks like this), then my ROI is wrong.

I’m using VTK 9.3.0. MWE follows

```auto
from vtkmodules.all import *
colors = vtkNamedColors()

class AnnotatorView:
    def __init__ (self) -> None:
        self.renderer = vtkRenderer()
        self.render_window = vtkRenderWindow()
        self.render_window.AddRenderer(self.renderer)
        self.render_window.SetWindowName('Annotator')
        self.render_window.SetSize(800, 800)

        self.interactor = vtkRenderWindowInteractor()
        self.interactor.SetRenderWindow(self.render_window)

        self.create_background()

    def create_background(self, width=800, height=800):
        image_data = vtkImageData()
        image_data.SetDimensions(width, height, 1)
        image_data.AllocateScalars(VTK_UNSIGNED_CHAR, 1)

        for y in range(height):
            for x in range(width):
                gradient = y / 800.0
                image_data.SetScalarComponentFromFloat(x, y, 0, 0, gradient * 255)

        actor = vtkImageActor()
        actor.GetMapper().SetInputData(image_data)
        self.renderer.AddActor(actor)

    def add_point_actor(self, image_coordinates, point_size=2):
        """ Add a sphere at the given image coordinates """
        source = vtkSphereSource()
        source.SetCenter(image_coordinates[0], image_coordinates[1], 0)
        source.SetRadius(point_size)

        mapper = vtkPolyDataMapper()
        mapper.SetInputConnection(source.GetOutputPort())

        # Create an panel_actor
        actor = vtkActor()
        actor.SetMapper(mapper)
        actor.GetProperty().SetColor(colors.GetColor3d("Red"))
        actor.GetProperty().SetDiffuse(1)
        actor.GetProperty().SetSpecular(1)
        self.renderer.AddActor(actor)
        return actor   

class AnnotatorInteractorStyle(vtkInteractorStyleImage):
    def __init__ (self, view, parent=None):
        self.is_dragging = False
        self.is_annotating = False
        self.dragged_points = []
        self.view = view

        self.AddObserver('LeftButtonPressEvent', self.left_button_press_event)
        self.AddObserver('KeyPressEvent', self.key_press_event)
        self.AddObserver('LeftButtonReleaseEvent', self.left_button_release_event)
        self.AddObserver("MouseMoveEvent", self.on_mouse_move_event)

    def key_press_event(self, obj, event):
        key = self.view.interactor.GetKeySym()
        if key == "a":
            self.is_annotating = True
        if key == "s":
            self.is_annotating = False

    def left_button_press_event(self, obj, event):
        if self.is_annotating:
            self.is_dragging = True

    def left_button_release_event(self, obj, event):
        if self.is_annotating:
            self.is_dragging = False

    def on_mouse_move_event(self, obj, event):
        if self.is_dragging:
            (mouseX, mouseY) = self.GetInteractor().GetEventPosition()
            # print(f'event position: {mouseX} , {mouseY}', flush=True)
            picker = vtkPointPicker()
            picker.Pick(mouseX, mouseY, 0.0, self.view.renderer)
            coords = picker.GetPickPosition()
            # print(f"image coords: {coords}")

            self.dragged_points.append(coords)
            self.view.add_point_actor(coords)
            self.view.render_window.Render()

if __name__ == " __main__":
    print("START")
    view = AnnotatorView()

    interactor_style = AnnotatorInteractorStyle(view)
    view.interactor.SetInteractorStyle(interactor_style)

    view.renderer.ResetCamera()
    view.render_window.Render()
    view.interactor.Initialize()
    view.interactor.Start()

    print("DONE")

```

Is this a VTK issue or is my code just not optimized?

(Our typical background images are 800\*600 or smaller)