# Pick and highlight glyphs.
**URL:** https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613
**Category:** Support
**Created:** [August 19, 2019, 12:51pm UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613 "2019-08-19T12:51:44Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Mskovmand](https://discourse.vtk.org/u/Mskovmand)
#### Post date: [August 19, 2019, 12:51pm UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/1 "2019-08-19T12:51:45Z")
Firstly, I’m still fairly new at VTK, I’m doing the best I can 🙂
I have a scene illustrating points as glyphs. I want to be able to pick and highlight each glyph individually.
I have implemented the interactor style highlighting actors, which works perfectly. However, this will select all glyphs at once.
I’m showing the points as glyphs since I normally have more than 10,000 points. And creating an individual actor for each point makes interaction impossible (simple operates to slow).
I looked into a vtkCellPicker, and I’m getting something, but it is definitely not correct, and I was hoping someone could assist me.
What I have:
```
import vtk
import numpy as np
class InteractorStyle(vtk.vtkInteractorStyleTrackballCamera):
def __init__ (self, glyphs, renderer):
self.glyphs = glyphs
self.renderer = renderer
self.AddObserver("LeftButtonPressEvent", self._left_button_press_event)
def _left_button_press_event(self, obj, event):
click_pos = self.GetInteractor().GetEventPosition()
cell_picker = vtk.vtkCellPicker()
cell_picker.Pick(click_pos[0], click_pos[1], 0, self.GetDefaultRenderer())
input_ids = self.glyphs.GetOutput().GetPointData().GetArray("InputPointIds")
if input_ids:
cell = self.glyphs.GetOutput().GetCell(cell_picker.GetCellId())
if cell and cell.GetNumberOfPoints() > 0:
input_id = cell.GetPointId(0)
selected_id = input_ids.GetTuple1(input_id)
if selected_id >= 0:
highlight_sphere = vtk.vtkSphereSource()
highlight_sphere.SetRadius(2)
highlight_sphere.SetThetaResolution(8)
highlight_sphere.SetPhiResolution(8)
highlight_sphere.SetCenter(self.glyphs.GetOutput().GetPoint(int(selected_id)))
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(highlight_sphere.GetOutputPort())
highlight_actor = vtk.vtkActor()
highlight_actor.SetMapper(mapper)
self.renderer.AddActor(highlight_actor)
print("Pick!")
self.OnLeftButtonDown()
return
renderer = vtk.vtkRenderer()
render_window = vtk.vtkRenderWindow()
render_window.AddRenderer(renderer)
interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(render_window)
sphere = vtk.vtkSphereSource()
sphere.SetRadius(1)
sphere.SetThetaResolution(8)
sphere.SetPhiResolution(8)
points = vtk.vtkPoints()
p_data = vtk.vtkPolyData()
for i in range(20):
points.InsertNextPoint(20 * np.random.random(3))
p_data.SetPoints(points)
glyph = vtk.vtkGlyph3D()
glyph.GeneratePointIdsOn()
glyph.SetInputData(p_data)
glyph.SetSourceConnection(sphere.GetOutputPort())
glyph.Update()
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(glyph.GetOutputPort())
actor = vtk.vtkActor()
actor.SetMapper(mapper)
renderer.AddActor(actor)
style = InteractorStyle(glyph, renderer)
style.SetDefaultRenderer(renderer)
interactor.SetInteractorStyle(style)
render_window.Render()
interactor.Start()
```
I add a sphere when something is clicked, at the found coordinates. This shows that the returned coordinates are not those I expected.
So, is this the wrong way to go about this issue?
If the CellPicker is the correct way, how can I extract the glyph and recolor it?
---
### Author:  [@marcomusy](https://discourse.vtk.org/u/marcomusy)
#### Post date: [August 19, 2019, 9:55pm UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/2 "2019-08-19T21:55:15Z")
Hi
just change
`highlight_sphere.SetCenter(self.glyphs.GetOutput().GetPoint(int(selected_id)))`
to
`highlight_sphere.SetCenter(self.glyphs.GetInput().GetPoint(int(selected_id)))`
---
### Author:  [@Mskovmand](https://discourse.vtk.org/u/Mskovmand)
#### Post date: [August 22, 2019, 11:11am UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/3 "2019-08-22T11:11:53Z")
I would like to reply an answer myself, for possible future readers.
I succeeded in picking and highlighting specific glyphs.
It still very basic, and needs refinement, but assuming the glyphs are colored by a scalar, from an array called ‘col’
```
class InteractorStyle(vtk.vtkInteractorStyleTrackballCamera):
def __init__ (self, glyphs, renderer):
self.glyphs = glyphs
self.renderer = renderer
self.AddObserver("LeftButtonPressEvent", self._left_button_press_event)
self._new_glyph_index = None
self._old_glyph_index = None
self._new_glyph_value = None
self._old_glyph_value = None
def _left_button_press_event(self, obj, event):
click_pos = self.GetInteractor().GetEventPosition()
cell_picker = vtk.vtkCellPicker()
cell_picker.Pick(click_pos[0], click_pos[1], 0, self.GetDefaultRenderer())
if self._new_glyph_value:
if self._old_glyph_value:
self.data.GetPointData().GetArray('col').SetValue(self._old_glyph_index, self._old_glyph_value)
self._new_glyph_index = self.glyph_data.GetOutput().GetPointData().GetArray("InputPointIds").GetValue(cell_picker.GetPointId())
self._new_glyph_value = self.data.GetPointData().GetArray('col').GetTuple1(self._new_glyph_index)
self.data.GetPointData().GetArray('col').SetValue(self._new_glyph_index, **number** )
self._old_glyph_index = self._new_glyph_index
self._old_glyph_value = self._new_glyph_value
self.data.Modified()
```
This interactor style did what I needed, The **number** needs to be replaced by a scalar value providing the desired color.
---
### Author:  [@Mskovmand](https://discourse.vtk.org/u/Mskovmand)
#### Post date: [August 22, 2019, 11:12am UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/4 "2019-08-22T11:12:36Z")
It worked, but I found a different approach instead. Thanks for the answer though!
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [February 3, 2020, 9:28am UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/5 "2020-02-03T09:28:14Z")
Hi Martin, can you tell me how were your another approach ? I have to make the same task, but I didn’t succeeded, and I intend to try in another way. Thank you.
---
### Author:  [@Mskovmand](https://discourse.vtk.org/u/Mskovmand)
#### Post date: [February 10, 2020, 6:45am UTC](https://discourse.vtk.org/t/pick-and-highlight-glyphs/1613/7 "2020-02-10T06:45:09Z")
I apologize for the confusion. The “other” approach is the one marked with the solution. It is a different approach than the one suggested by Marcomusy.