[vtkusers] Getting the scalar value from vtkCell

[Mark Kobine]

Hi Dominik,

My geometry is arranged into a number of STL "solid" sections each of
which is comprised of many triangles. When the user clicks on the
geometry I want to "highlight" the whole "solid" section, not just the
individual triangle. The one thing that all the triangles in the same
section have in common is their scalar value. So I thought that I
may be able to use that.

Hope that helps to explain my thinking.

Many thanks,
Mark

Dominik Szczerba wrote:
> Hi Mark,
> I am not sure what you are after. Why do you need to have cells with the
> same scalar? I thought you just wanted to highlight a picked cell (or
> cells). In any case, you can get the scalar value by
> dataset->GetCellData()-> ... and getting you array by name for example.
> But I dont see why you would want that. You can extract the selected
> cell's edges and color their actor to your liking.
> - Dominik
> 
> Mark Kobine wrote:
>> Hi Dominik,
>>
>> Thanks for that - vtkExtractEdges looks like the way to go.
>>
>> What I think I need to do next is to get the set of cells that share the
>> same scalar value (as allocated by vtkSTLReader with ScalarTagsOn())
>> when the STL file was read in. I can get the cell the user clicked
>> easily with vtkCellPicker but I haven't been able to find anything that
>> will give me that cell's scalar value or the rest of the cells with the
>> same scalar.
>>
>> Or am I approaching this the wrong way?
>>
>> Many thanks,
>> Mark
>>
>> Dominik Szczerba wrote:
>>> Hi Mark,
>>> Please make cc's to the mailing list.
>>> The easiest thing to set up (not necessarily the fastest to perform)
>>> would be to extract the picked selection and use the vtkExtractEdges
>>> filter on it. Then set linewidth to 2 or 3 and color to red in a
>>> corresponding actor.
>>> bye, Dominik
>>>
>>> Mark Kobine wrote:
>>>> Hi Dominik,
>>>>
>>>> Many thanks for the advice.
>>>>
>>>> If I were to go about plotting the edges of the selected geometry, as
>>>> you suggest, how would I go about this?
>>>>
>>>> Many thanks,
>>>> Mark
>>>>
>>>> Dominik Szczerba wrote:
>>>>> This has been frequently asked here. There is no way to change a cell
>>>>> color other than to change its scalar value. This is not elegant as you
>>>>> have to write to your original dataset, supposedly writing down the
>>>>> overwritten value temporarily and taking care it is written back when
>>>>> you un-pick. Then, you have to remember that the modified scalar has
>>>>> still go through a color lookup table to be seen and having it always
>>>>> e.g. red may not always be that trivial and robust.
>>>>> I would recommend a different way without modifying the actual data,
>>>>> like shrinking the element, plotting it edges, or annotating it's
>>>>> nodes etc.
>>>>> - Dominik
>>>>>
>>>>> Mark Kobine wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I have some geometry read in from an STL file that contains several
>>>>>> "solid" sections. These sections are currently coloured automatically
>>>>>> by vtk based on the scalar value assigned to each section as it is
>>>>>> read in. I want to change the appearance of one of these sections if
>>>>>> the user clicks on it in the renderer window.
>>>>>>
>>>>>> I'm using vtkCellPicker and from that I can get the selected vtkCell.
>>>>>> From there is there a way to get the scalar value for that cell?
>>>>>>
>>>>>> My approach is to use that scalar to somehow change the appearance of
>>>>>> all cells with the same scalar value.
>>>>>>
>>>>>> Can any one help? Is this a sensible approach?
>>>>>>
>>>>>> Many thanks,
>>>>>> Mark
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>