# unexpected behavior when selecting (and "highlighting") cells in trame

**URL:** https://discourse.vtk.org/t/unexpected-behavior-when-selecting-and-highlighting-cells-in-trame/10333
**Category:** Support
**Tags:** python
**Created:** [December 28, 2022, 5:21pm UTC](https://discourse.vtk.org/t/unexpected-behavior-when-selecting-and-highlighting-cells-in-trame/10333 "2022-12-28T17:21:10Z")
**Posts on this page:** 1
**Showing post:** 8

<div class="post-metadata">

### Author: ![Robert\_Collar](https://discourse.vtk.org/user_avatar/discourse.vtk.org/robert_collar/32/6256_2.png) [@Robert\_Collar](https://discourse.vtk.org/u/Robert_Collar)
#### Post date: [January 16, 2023, 1:26am UTC](https://discourse.vtk.org/t/unexpected-behavior-when-selecting-and-highlighting-cells-in-trame/10333/8 "2023-01-16T01:26:44Z")

</div>

Hi all,

I’ve managed to resolve my second question above using the code found at the end of this message. The gist is that I assigned an “ID” to each cell of the `vtkPolyLine` object by attaching a data array to the object. As this array persists through the application of the tube filter, I can then conduct a selection based on this ID array, thus allowing me to grab all cells in the output of the tube filter that correspond to one cell in the `vtkPolyLine` object!

```nohighlight
import vtk
from trame.app import get_server
from trame.widgets import vuetify, vtk as vtk_widgets
from trame.ui.vuetify import SinglePageLayout

from vtkmodules.vtkRenderingCore import (
    vtkActor,
    vtkPolyDataMapper,
    vtkDataSetMapper,
    vtkRenderer,
    vtkRenderWindow,
    vtkRenderWindowInteractor, 

    vtkCellPicker
)
from vtkmodules.numpy_interface import dataset_adapter as dsa
from vtkmodules.vtkFiltersCore import vtkTubeFilter
from vtkmodules.vtkFiltersExtraction import vtkExtractSelection
from vtkmodules.vtkCommonDataModel import vtkSelection, vtkSelectionNode

import vtk.util.numpy_support as vtknumpy
import numpy as np

# -----------------------------------------------------------------------------
# Generate dataset
# -----------------------------------------------------------------------------

points = vtk.vtkPoints()
points.SetNumberOfPoints(4)
line = vtk.vtkLine()
lines = vtk.vtkCellArray()

# create first line segment
points.SetPoint(0, 0, 0, 0)
line.GetPointIds().SetId(0, 0)

points.SetPoint(1, 1, 1, 1)
line.GetPointIds().SetId(1, 1)

lines.InsertNextCell(line)

# create second line segment
points.SetPoint(2, 1, 1, 1)
line.GetPointIds().SetId(0, 2)

points.SetPoint(3, 2, 2, 2)
line.GetPointIds().SetId(1, 3)

lines.InsertNextCell(line)

linesPolyData = vtk.vtkPolyData()
linesPolyData.SetPoints(points)
linesPolyData.SetLines(lines)

vtkfields= vtknumpy.numpy_to_vtk([0,1])
vtkfields.SetName("og_id")
vtkfields.SetNumberOfComponents(1)

og_ids = vtknumpy.numpy_to_vtk([0,1]) # TODO: change to be a function of number of lines
og_ids.SetName("og_id")
og_ids.SetNumberOfComponents(1)
linesPolyData.GetCellData().AddArray(og_ids)

# -----------------------------------------------------------------------------
# Trame initialization
# -----------------------------------------------------------------------------

server = get_server()
state, ctrl = server.state, server.controller

# -----------------------------------------------------------------------------
# Interactions
# -----------------------------------------------------------------------------

def update_selection(pickData, **kwargs): 
    data = pickData
    picker = vtkCellPicker()
    picker.SetTolerance(0.0005) # based on example
    pos = data["position"]
    picker.Pick(pos["x"], pos["y"], pos["z"], renderer)
    idx = picker.GetCellId() 

    if idx != -1: 
            SELECTED_IDX = np.array(tubes_filter.GetOutput().GetCellData().GetArray("og_id"))[idx].tolist()
    else: 
        SELECTED_IDX = []

    sel_node = vtkSelectionNode()
    sel_node.GetProperties().Set(vtkSelectionNode.CONTENT_TYPE(), vtkSelectionNode.VALUES)
    sel_node.GetProperties().Set(vtkSelectionNode.FIELD_TYPE(), vtkSelectionNode.CELL)
    sel_node.GetProperties().Set(vtkSelectionNode.COMPONENT_NUMBER(), 0)

    selected_cells = vtknumpy.numpy_to_vtk(SELECTED_IDX)
    selected_cells.SetName("og_id")
    selected_cells.SetNumberOfComponents(1)
    sel_node.SetSelectionList(selected_cells)

    sel = vtkSelection()
    sel.AddNode(sel_node)

    selection_extract.SetInputConnection(tubes_filter.GetOutputPort())
    selection_extract.SetInputDataObject(1, sel)
    selection_extract.Update()
    selection_actor.SetVisibility(1)

    # Update 3D view
    ctrl.view_update()

# -----------------------------------------------------------------------------
# VTK pipeline
# -----------------------------------------------------------------------------

tubes_filter = vtkTubeFilter()
tubes_filter.SetInputData(linesPolyData)
radius = 2
tubes_filter.SetRadius(radius)
n_of_sides = 3
tubes_filter.SetNumberOfSides(n_of_sides)
tubes_filter.Update()

mapper = vtkPolyDataMapper()
mapper.SetInputConnection(tubes_filter.GetOutputPort())
actor = vtkActor()
actor.SetMapper(mapper)

# Selection
selection_extract = vtkExtractSelection()
selection_mapper = vtkDataSetMapper()
selection_mapper.SetInputConnection(selection_extract.GetOutputPort())
selection_actor = vtkActor()
selection_actor.GetProperty().SetColor(1, 0, 1)
selection_actor.SetMapper(selection_mapper)
selection_actor.SetVisibility(0)
selection_actor.SetPickable(0)

renderer = vtkRenderer()
renderer.SetBackground(1, 1, 1)
render_window = vtkRenderWindow()
render_window.AddRenderer(renderer)

rw_interactor = vtkRenderWindowInteractor()
rw_interactor.SetRenderWindow(render_window)
rw_interactor.GetInteractorStyle().SetCurrentStyleToTrackballCamera()

renderer.AddActor(actor)
renderer.AddActor(selection_actor)
renderer.ResetCamera()

# -----------------------------------------------------------------------------
# GUI layout
# -----------------------------------------------------------------------------

VTK_VIEW_SETTINGS = {
    "interactive_ratio": 1,
    "interactive_quality": 100,
}

with SinglePageLayout(server) as layout:
    layout.icon.click = ctrl.view_reset_camera

    with layout.content:
        with vuetify.VContainer(fluid=True, classes="fill-height pa-0 ma-0"):
            view = vtk_widgets.VtkRemoteView(
                render_window,
                interactor_events=("events", ["LeftButtonPress"]), 
                LeftButtonPress=(update_selection, "[utils.vtk.event($event)]"),
                **VTK_VIEW_SETTINGS,
            )
            ctrl.view_update = view.update
            ctrl.view_reset_camera = view.reset_camera

# -----------------------------------------------------------------------------
# Main
# -----------------------------------------------------------------------------

if __name__ == " __main__":
    server.start(port=0)

```

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