[vtkusers] vtkCubeAxesActor positions text labels incorrectly on axis

[David Lonie]

Hi Michael,

Looking at our change log, it doesn't appear that the vtkCubeAxesActor has
seen many significant changes since 6.1, so I doubt a newer version would
work any differently. I'm not aware of anyone currently working on this
class, but I do know that there is a replacement in development in
ParaView, vtkGridAxes3DActor:

https://github.com/Kitware/ParaView/blob/master/ParaViewCore/VTKExtensions/Default/vtkGridAxes3DActor.h

There's been talk of moving it into VTK, but I'm not aware of any firm
plans at this point.

In the meantime, feel free to file a bug report / feature request for this
so it doesn't get lost.

Dave

On Fri, Jun 24, 2016 at 7:12 AM, Michael Arnold <myk321 at gmail.com> wrote:

> Sorry - my bad:
>     cubeAxesActor->SetXAxisRange(0.0, Labels.size() * 1.0);
> needs to be:
>     cubeAxesActor->SetXAxisRange(1.0, Labels.size() * 1.0);
>
> Michael
>
>
> -----------------------------------------------------------------------------------------
>
> Problem: for axis labels created using vtkCubeAxesActor, if we have more
> than 10 text labels, the labels and the data don't line-up, because the
> labels are positioned incorrectly on the axis.
>
> What are we Getting in more Detail:
> (a) If we have 9 data points (<10) we get 9 label points, with the last
> label at the end of the axis.  So the labels can be 1,2,3,4,5,6,7,8,9,
> which lines-up nicely with the data: all is good in the world.
> (b) If we have 10 data points, we get get 6 labels points with the last
> label one at the end of the axis.  We compute a label skip factor of 2.  We
> start at the beginning of the axis.  We label 1,3,5,7,9,11 <- what category
> is this last label?? We only have 10 data points!  So the last data label
> does not line-up with its data.
> (c) If we have 11 data points, we again get 6 label points with the last
> label positioned a short distance back from the end of the axis.  Again we
> compute a label skip factor of 2.  We begin to label at the beginning of
> the axis.  So we get 1,3,5,7,9,11.  Ok, because we had 11 data-points, but
> now we land-up with the label for the last data element being back from the
> end of the axis i.e. the data label does not line-up with its data.
>
> What we want:
> (a) VTK seems to make a quite reasonable assumption to limit the number of
> labels to less than 10, so lets stick with that.
> (b) VTK works fine with data sets with 9 or fewer elements, so lets focus
> on data-sets with 10 or more data-points.
> (c) We need to handle data-sets with an even count of elements slightly
> differently from data-sets with an odd count of elements.  (For a more
> generic handling this would be if the count of the elements is divisible by
> the skip factor, but for the moment lets stick to a skip factor of 2 and
> thus even or odd element counts).
> (d) For a data-set with an odd count of elements (lets say 11) we can
> easily imagine the handling to be:
> Smallest at the start (e.g. 1)
> Biggest at the end (eg. 11)
> Then fill-in the labels using the skip factor (2 in this case), so we get
> something like 1,3,5,7,9,11
> (e) For a data-set with an even count of elements (lets say 10), we need to
> have a gap between the last label and the end of the axis.  The end of the
> axis seems most logical place for this gap, so the last label point is back
> a bit from the end of the axis.  So:
> Smallest at the start (e.g. 1)
> Then fill in the labels using the skip factor, so something like 1,3,5,7,9
> and we happily land-up with a label of 9 being a bit back from the end of
> the axis.
>
> So what was the difference between what we want and what we are getting?
> The problem is not about the calculation of the number of labels - that is
> fine.
> The problem is the positioning of the labels on the axis - is the last
> label at the end of the axis or bit back from the end?
> Today, for data-sets with an even number of elements, we are getting the
> last label at the end of the axis.  This is incorrect because for an even
> number of elements, we want the last label to be positioned back from the
> end of axis.
> Today, for data-sets with odd number of elements, we are getting the last
> label positioned with a gap before the end of the axis.  Again this is
> incorrect, because the label should be positioned at the end of the axis.
>
> Questions:
> I'm using an old'ish version of VTK 6.1 - has this issue been fixed in a
> newer version?
> Am I misunderstanding something or can I raise a defect for this?
>
> Some Code:
>
> vtkSmartPointer<vtkCubeAxesActor> cubeAxesActor =
> vtkSmartPointer<vtkCubeAxesActor>::New();
> cubeAxesActor->SetBounds(outputPolyData->GetBounds());
> cubeAxesActor->SetCamera(Renderer->GetActiveCamera());
> cubeAxesActor->GetTitleTextProperty(0)->SetColor(1.0, 1.0, 1.0);    //White
> cubeAxesActor->GetLabelTextProperty(0)->SetColor(1.0, 1.0, 1.0);    //White
> cubeAxesActor->SetXTitle("X-Axis");
> cubeAxesActor->GetXAxesGridlinesProperty()->SetColor(1.0, 1.0, 1.0);
> //White
>
> cubeAxesActor->DrawXGridlinesOn();
> cubeAxesActor->SetGridLineLocation(VTK_GRID_LINES_FURTHEST);
> cubeAxesActor->SetFlyModeToOuterEdges();        //Place the axes on the
> outer edges of the cube
>
> //Set the labels on the x-axis
> vtkSmartPointer<vtkStringArray> XAxisLabels =
> vtkSmartPointer<vtkStringArray>::New();
> std::vector<std::string> Labels = ResultsServer->GetXLabels();    //Get a
> list of axis labels
> if (!Labels.empty()) {
>
>     int32_t SkipFactor = (Labels.size() / 10) + 1;
>     int32_t Counter = 0;
>
>     //Evenly divisble
>     for (auto LabelsIt = std::begin(Labels); LabelsIt != std::end(Labels);
> ++LabelsIt)
>         if (Counter++ % SkipFactor == 0)
>             XAxisLabels->InsertNextValue(LabelsIt->c_str());
>
>     cubeAxesActor->SetXAxisRange(0.0, Labels.size() * 1.0);
>     cubeAxesActor->GetLabelTextProperty(0)->SetFontSize(20);
>     cubeAxesActor->GetLabelTextProperty(0)->SetOrientation(90.0);
>     cubeAxesActor->SetAxisLabels(0, XAxisLabels);
>
>     Labels.clear();
> }
>
> Kind regards,
> Michael
>
>
>
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