Checking for contours of zero size

Support
1

This is a follow on off vtkContourGrid example - #7 by BlueKnight7 and requires a little background detail first.

I’ve setup my code to have multiple mesh objects using vtkUnstructuredGrid’s. I want to be able to create contours, but I know that some contours will not exist in some vtkUnstructuredGrid objects. Is there a way to check the vtkContourFilter (object) or the resulting vtkPolyDataMapper (object) to determine if there is anything there to display? I couldn’t spot anything in the online documentation for these 2 classes that would give me a size that I could check. It’s possible that I’m not looking at the right place.

With how I have this coded at the moment, I have a bunch of zero-sized contours / mappers that are created but aren’t displayed with the actors that are created from them. By zero-size, I mean that the objects exist, but they don’t contain any information that is displayed.

I’m open to suggestion on how to deal with the situation that I’ve just described.

2

Roger,

You could look at the data object output from the vtkContourFilter and check for the number of cells being greater than 0, eg.

vtkNew<vtkContourFilter> contour;
...
contour->Update();
vtkPolyData* pd = contour->GetOutput();
if (pd->GetNumberOfCells() < 1)
{
  // skip creation of mapper/actor
}

Hope that helps.

3

Cory,

That worked. Although, I would prefer that the vtkContourFilter GenerateValues function return something like a boolean: true is success in generating contours or false for no contours generated.

BK