# How to draw a line by clicking some scattered points
**URL:** https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225
**Category:** Development
**Created:** [March 2, 2018, 5:51am UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225 "2018-03-02T05:51:39Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@spring](https://discourse.slicer.org/u/spring)
#### Post date: [March 2, 2018, 5:51am UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/1 "2018-03-02T05:51:39Z")
Hi All,
I want to draw a line by connecting some scattered points which I have clicked in the view.
I can get each points RAS position, but it seems can not display the final line in Slicer, below is my code for drawing line, could someone share some guidance?
```auto
#coding----
def drawPolyLine(points):
#points is the list which contains each points pos,likes [(0.0,1.0),(1.0,2.0)],just one slice in the view.
polyLine = vtk.vtkPolyLineSource()
for i, (x, y) in enumerate(points):
polyLine.SetPoint(i, x, y, 0)
polyLine.SetNumberOfPoints(len(points))
polyLine.SetClosed(True)
polyLine.Update()
polyData = polyLine.GetOutput()
return showPolyData(polyData)
def showPolyData(polyData):
model = slicer.vtkMRMLModelNode()
if isinstance(polyData, vtk.vtkAlgorithmOutput):
model.SetPolyDataConnection(polyData)
elif isinstance(polyData, vtk.vtkPolyData):
# print("type and polyData={},{}".format(type(polyData),polyData))
model.SetAndObservePolyData(polyData)
else:
raise Exception('input error!')
model.SetScene(slicer.mrmlScene)
modelDisplay = slicer.vtkMRMLModelDisplayNode()
modelDisplay.SetOpacity(1.0)
modelDisplay.SetColor([1, 1, 0])
modelDisplay.SetSliceIntersectionVisibility(True) # Show in slice view
modelDisplay.SetVisibility(True) # Hide in 3D view
modelDisplay.SetScene(slicer.mrmlScene)
slicer.mrmlScene.AddNode(modelDisplay)
slicer.mrmlScene.AddNode(model)
transform = slicer.vtkMRMLLinearTransformNode()
slicer.mrmlScene.AddNode(transform)
model.SetAndObserveDisplayNodeID(modelDisplay.GetID())
model.SetAndObserveTransformNodeID(transform.GetID())
return model
```
Thanks in advance!
Chunbo
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [March 2, 2018, 12:48pm UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/2 "2018-03-02T12:48:49Z")
You can use MarkupsToModel extension to create curves from markup fiducial or model points. It supports linear and various smooth interpolating and approximating methods.
---
### Author:  [@spring](https://discourse.slicer.org/u/spring)
#### Post date: [March 5, 2018, 7:19am UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/3 "2018-03-05T07:19:16Z")
@lassoan Thanks for your answer.
I have tried MarkupsToModel,it really can draw the straight line by clicking scattered pointes.
Just have one issue:if I want to delete the total polydata,I should switch to Models then select corresponding model to delete it,correct?
I have implemented a simple module,which can draw some scattered points,then connect neighboring points with a straight line, used a polydata to show these lines at last,likes below screenshot:
Since I want to setAndobserve this polydata in Slicer,the issue: this Polydata can not be displayed,since the area is 0,likes below screenshot:
Not sure if some parameters are incorrect? Or if there is some examples which can create a polydata and can be set and observed in Slicer?
Best，
Chunbo
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [March 5, 2018, 1:40pm UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/4 "2018-03-05T13:40:17Z")
If you set the output to be a closed surface instead of a line then you’ll get the surface area. Both sides of the surface will be included in the computation, so you probably want to divide the reported surface area by 2.
---
### Author:  [@spring](https://discourse.slicer.org/u/spring)
#### Post date: [March 5, 2018, 2:54pm UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/5 "2018-03-05T14:54:14Z")
Thanks,Lasson.
I will try the method.
Btw,I have solved my issue from this post:[Display model in slice viewer](https://discourse.slicer.org/t/display-model-in-slice-viewer/208/2).
Best,
Chunbo
---
### Author:  [@spring](https://discourse.slicer.org/u/spring)
#### Post date: [March 6, 2018, 8:34am UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/6 "2018-03-06T08:34:55Z")
Hi lassoan,
I used the following codes :
inputMarkups = getNode(‘F’)
outputModel = slicer.mrmlScene.AddNode(slicer.vtkMRMLModelNode())
outputModel.CreateDefaultDisplayNodes()
outputModel.GetDisplayNode().SetSliceIntersectionVisibility(True)
outputModel.GetDisplayNode().SetColor(1,0,0)
markupsToModel = slicer.mrmlScene.AddNode(slicer.vtkMRMLMarkupsToModelNode())
markupsToModel.SetAutoUpdateOutput(True)
markupsToModel.SetAndObserveModelNodeID(outputModel.GetID())
markupsToModel.SetAndObserveMarkupsNodeID(inputMarkups.GetID())
* * *
It can create curves with clicking points,one issue is:the curve is convex hull,can we change it to false?
since we found some points can not be seen,pls see below screenshots:
Thanks,
Chunbo
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [March 10, 2018, 2:06pm UTC](https://discourse.slicer.org/t/how-to-draw-a-line-by-clicking-some-scattered-points/2225/7 "2018-03-10T14:06:48Z")
Do you need a line/curve connecting points? If yes, then set ModelType to Curve and probably enable TubeLoop as well.
If you want to reconstruct a surface from a sparse set of points then Delaunay triangulation is used. You can tune DelaunayAlpha parameter to control how much concavity is allowed in the reconstructed surface (if alpha is set to 0 then the result will be a convex hull).