[vtkusers] Fwd: How to generate a surface normal glyph for a triangle cell

[Amy Squillacote]

Hi Elvis,

I'm copying this back to the vtkusers list. Please keep the discussion 
on the list so other people can contribute to it and so it's archived 
for future reference.

- Amy

Elvis Dowson wrote:
> Hi Amy,
>                   Yes, I realized later that I had to turn orient on. 
> I have a very fundamental question, the sample that Miguel pointed me 
> to uses vtkPolyDataNormals to compute the normals of the plane source, 
> and since the plane source has four vertices, four glyphs get generated. 
>
> However, the plane source has a GetNormal() method, which will return 
> the x, y, z coordinates of it's surface normal. I tried to directly 
> create a vktPolyData structure and inserted the plane source normal 
> and try to get it to display the surface normal, but it kept orienting 
> the wrong way, even after I turned orient on for the 3D glyph. 
>
> Any ideas why?  
>
> The source code can be found below.
>
> Best regards,
>
> Elvis Dowson
>
> Begin forwarded message:
>
>> *From: *Elvis Dowson <elvis.dowson at mac.com <mailto:elvis.dowson at mac.com>>
>> *Date: *October 8, 2008 3:49:33 PM GMT+04:00
>> *To: *marf at itccanarias.org <mailto:marf at itccanarias.org>
>> *Cc: *vtkusers at vtk.org <mailto:vtkusers at vtk.org>
>> *Subject: **Re: [vtkusers] How to generate a surface normal glyph for 
>> a triangle cell*
>>
>> Hi Miguel,
>>                      Thanks for the tip. It works when I use 
>> vtkPolyDataMapper as shown below. However, you the plane has a 
>> methods that returns the surface normal, which is a single surface 
>> normal. How can I pipe this surface normal data, directly to be 
>> generated as a single glyph? 
>>
>> The spikeF.tcl example code uses vtkMaskPoints to reduce the number 
>> of sampled points for generating the surface normal.
>>
>> In my specific case of the plane source, the surface normal is 
>> already available to me. I don't need to use vtkPolyDataMapper to 
>> generate the surface normals. How can I use the existing surface 
>> normal information from the plane source to generate a single glyph 
>> that represents the surface normal?
>>
>> If I use vtkPolyDataMapper, it will generate 4 glyphs corresponding 
>> to the surface normals at each of the four vertices of the plane. I 
>> just want to render one glyph corresponding to the surface normal 
>> computed from the central surface of the plane source.
>>
>> Best regards,
>>
>> Elvis Dowson 
>>
>> *Example TCL Code:*
>>
>> # This example shows how to manually construct a plane and display 
>> its surface normal 
>> # using Tcl. 
>> #
>>
>> package require vtk
>> package require vtkinteraction
>>
>> # Create a plane source
>> vtkPlaneSource planeSource
>>
>> vtkPolyDataNormals planeNormals
>>   planeNormals SetInputConnection [planeSource GetOutputPort]
>>  
>> vtkDataSetMapper planeMapper
>>   planeMapper SetInputConnection [planeNormals GetOutputPort]
>>
>> vtkActor planeActor
>>   planeActor SetMapper planeMapper
>>
>> # Create an arrow glyph to represent the surface normal
>> # -----------------------------------------------------
>>
>> # Specify the location of the glyph
>> #vtkPolyData arrowGlyphPolyData
>> #vtkPoints   arrowGlyphPoints
>>   #arrowGlyphPolyData SetPoints arrowGlyphPoints
>>   #arrowGlyphPoints InsertNextPoint 1 1 0
>>   #eval arrowGlyphPoints InsertNextPoint [planeSource GetNormal]
>>
>> # Specify the shape of the glyph
>> vtkArrowSource arrowSource
>>
>> vtkGlyph3D arrowGlyph
>>   arrowGlyph ScalingOn
>>   arrowGlyph SetScaleFactor 0.7
>>   arrowGlyph SetVectorModeToUseNormal
>>   arrowGlyph SetScaleModeToScaleByVector
>>   arrowGlyph OrientOn
>>   arrowGlyph SetSourceConnection [arrowSource GetOutputPort]
>>   arrowGlyph SetInputConnection  [planeNormals GetOutputPort]
>>
>> vtkDataSetMapper arrowGlyphMapper
>>   arrowGlyphMapper SetInputConnection [arrowGlyph GetOutputPort]
>>
>> vtkActor glyphActor
>>   glyphActor SetMapper arrowGlyphMapper
>>
>>
>> # Create the usual rendering stuff.
>> vtkRenderer ren1
>> vtkRenderWindow renWin
>>   renWin AddRenderer ren1
>>   renWin SetSize 300 150
>> vtkRenderWindowInteractor iren
>>   iren SetRenderWindow renWin
>>
>> #ren1 SetBackground .1 .2 .4
>>
>> ren1 AddActor planeActor
>> ren1 AddActor glyphActor
>>
>> ren1 ResetCamera
>> ren1 ResetCameraClippingRange
>>
>> renWin Render
>>
>> # render the image
>> #
>> iren AddObserver UserEvent {wm deiconify .vtkInteract}
>> iren Initialize
>> wm withdraw .
>>
>>
>>

-- 
Amy Squillacote                    Phone: (256) 726-4839
Computer Scientist                 Fax: (256) 726-4806
CFD Research Corporation           Web: http://www.cfdrc.com
215 Wynn Drive, Suite 501
Huntsville, AL  35805