# Issue Using StreamTracer with Calculator

**URL:** https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877
**Category:** Support
**Created:** [May 14, 2024, 5:39am UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877 "2024-05-14T05:39:33Z")
**Posts on this page:** 8
**Page:** 1

<div class="post-metadata">

### Author: ![Ludo](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/l/5f9b8f/32.png) [@Ludo](https://discourse.vtk.org/u/Ludo)
#### Post date: [May 14, 2024, 5:39am UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/1 "2024-05-14T05:39:33Z")

</div>

Hello everyone  
I’m trying to create streamline for both Scalar and Vector array.  
I have no issue when my data array is scalar but I have issue when handling Vector.  
My issue is that for Vector, after getting PolyData from StreamTracer output, the number of array from Point Data return 0.  
Below is the code I’m using.  
Could you please tell me what I’m doing wrong?

```cpp
bool bArrayIsVector = TargetDataArray.GetNumberOfComponents() == 3;

//first run Calculator
string FeatureName = TargetDataArray.GetName();
string Function = "iHat*" + FeatureName + "+jHat*" + FeatureName + "+kHat*" + FeatureName;

vtkArrayCalculator Calculator = vtkArrayCalculator.New();
if(!bArrayIsVector)
{
    Calculator.SetInputData(DataSet);
    Calculator.AddScalarArrayName(FeatureName, 0);
    Calculator.SetFunction(Function);
    Calculator.SetResultArrayName("vector_attr");
    Calculator.Update();
}
else
{
    Calculator.SetInputData(DataSet);
    Calculator.AddVectorArrayName(FeatureName, 0, 1, 2);
    Calculator.SetFunction(Function);
    Calculator.SetResultArrayName("vector_attr");
    Calculator.Update();
}

//set plane source
vtkPlaneSource planeSource = vtkPlaneSource.New();
[...]

//set streamtracer
vtkStreamTracer StreamTracer = vtkStreamTracer.New();
StreamTracer.SetInputConnection(Calculator.GetOutputPort());
StreamTracer.SetSourceConnection(planeSource.GetOutputPort());
StreamTracer.SetIntegratorTypeToRungeKutta45();
StreamTracer.SetIntegrationDirectionToForward();
StreamTracer.SetComputeVorticity(true);
StreamTracer.SetMaximumPropagation(StreamlineLengthPropagation);
StreamTracer.SetInitialIntegrationStep(0.3);
vtkInformationVector inArrayVec = StreamTracer.GetInformation().Get(vtkAlgorithm.INPUT_ARRAYS_TO_PROCESS());
vtkInformation inArrayInfo = inArrayVec.GetInformationObject(0);
inArrayInfo.Set(vtkDataObject.FIELD_NAME(), "vector_attr");
StreamTracer.Update();

//get polydata
vtkPolyData MyData = StreamTracer.GetOutput();
StreamTracer.Update();
MyData.BuildCells();
MyData.BuildLinks(0);
 
vtkPointData PointDatas = MyData.GetPointData();
int NbArray = PointDatas.GetNumberOfArrays(); // ->NbArray is 0 if array is vector

```

below is the error from the OutputWindow

> ```
> ERROR: In C:\Users\Lucas\Projects\Unity\CI\VTK-9.0.1\Common\Misc\vtkFunctionParser.cxx, line 238
> vtkFunctionParser (00000248BDC2C920): multiply expecting either 2 scalars or a scalar and a vector
> 
> ERROR: In C:\Users\Lucas\Projects\Unity\CI\VTK-9.0.1\Common\Misc\vtkFunctionParser.cxx, line 133
> vtkFunctionParser (00000248BDC2C920): Parse: Error deciding between ambiguous operators
> 
> ERROR: In C:\Users\Lucas\Projects\Unity\CI\VTK-9.0.1\Common\Misc\vtkFunctionParser.cxx, line 238
> vtkFunctionParser (00000248BDC2C920): multiply expecting either 2 scalars or a scalar and a vector
> 
> ERROR: In C:\Users\Lucas\Projects\Unity\CI\VTK-9.0.1\Common\Misc\vtkFunctionParser.cxx, line 133
> vtkFunctionParser (00000248BDC2C920): Parse: Error deciding between ambiguous operators
> 
> Warning: In C:\Users\Lucas\Projects\Unity\CI\VTK-9.0.1\Filters\Core\vtkArrayCalculator.cxx, line 348
> vtkArrayCalculator (0000024952EBFBE0): An error occurred when parsing the calculator’s function. See previous errors.
> 
> ```

I really thank you in advance for your help

---

<div class="post-metadata">

### Author: ![Ludo](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/l/5f9b8f/32.png) [@Ludo](https://discourse.vtk.org/u/Ludo)
#### Post date: [May 14, 2024, 6:30am UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/3 "2024-05-14T06:30:09Z")

</div>

For 2 Vectors, correct operator isn’t ‘\*’ but ‘.’ so my function will be  
Function = “iHat.” + FeatureName + “+jHat.” + FeatureName + “+kHat.” + FeatureName;

however when running the application I’ve got the following error lot of time before getting the result

> ERROR: In c:\users\lucas\projects\unity\ci\vtk-9.0.1\common\core\vtkGenericDataArray.txx, line 700  
> vtkDoubleArray (0000024950D55A70): Number of components for input and output do not match.  
> Source: 1  
> Destination: 3

Any idea why this happen?

---

<div class="post-metadata">

### Author: ![Paulo\_Carvalho](https://discourse.vtk.org/user_avatar/discourse.vtk.org/paulo_carvalho/32/370_2.png) [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [May 14, 2024, 10:11pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/4 "2024-05-14T22:11:30Z")

</div>

Hello,

Can you, please, enclose the code between a **```cpp** and a **```**? This will make the code much more readable.

best,

PC

---

<div class="post-metadata">

### Author: ![Ludo](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/l/5f9b8f/32.png) [@Ludo](https://discourse.vtk.org/u/Ludo)
#### Post date: [May 14, 2024, 10:28pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/5 "2024-05-14T22:28:10Z")

</div>

Hello  
Thank you for telling me about ` ``cpp and a ```, I didn’t know this I could use this one.  
I have edited my original post

Best regards

---

<div class="post-metadata">

### Author: ![Paulo\_Carvalho](https://discourse.vtk.org/user_avatar/discourse.vtk.org/paulo_carvalho/32/370_2.png) [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [May 14, 2024, 10:49pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/6 "2024-05-14T22:49:13Z")

</div>

Try to reduce the function to a trivial case:

```auto
string Function = "0.0";

```

See whether this works.

---

<div class="post-metadata">

### Author: ![Ludo](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/l/5f9b8f/32.png) [@Ludo](https://discourse.vtk.org/u/Ludo)
#### Post date: [May 14, 2024, 10:51pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/7 "2024-05-14T22:51:51Z")

</div>

Thank you for your help.  
I’m still getting the following error in the output windows

> ERROR: In c:\users\lucas\projects\unity\ci\vtk-9.0.1\common\core\vtkGenericDataArray.txx, line 700  
> vtkDoubleArray (0000021810CD5DA0): Number of components for input and output do not match.  
> Source: 1  
> Destination: 3

---

<div class="post-metadata">

### Author: ![Paulo\_Carvalho](https://discourse.vtk.org/user_avatar/discourse.vtk.org/paulo_carvalho/32/370_2.png) [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [May 15, 2024, 2:11pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/8 "2024-05-15T14:11:46Z")

</div>

Which line of code triggers the error?

---

<div class="post-metadata">

### Author: ![Ludo](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/l/5f9b8f/32.png) [@Ludo](https://discourse.vtk.org/u/Ludo)
#### Post date: [May 15, 2024, 10:48pm UTC](https://discourse.vtk.org/t/issue-using-streamtracer-with-calculator/13877/9 "2024-05-15T22:48:37Z")

</div>

Hello  
The error was triggered on the following line

```cpp
StreamTracer.Update();

```

I was able to fix the error by addind the following code before calling StreamTracer.Update()

```cpp
if (bArrayIsVector)
{
    inArrayInfo.Set(vtkDataObject.FIELD_NAME(), FeatureName);
}

```

Below is the working solution

```cpp
bool bArrayIsVector = TargetDataArray.GetNumberOfComponents() == 3;

vtkDataSet DataSet = MyReader.GetOutput();

string FeatureName = TargetDataArray.GetName();
string ResultDataArrayName = "vector_attr";
vtkArrayCalculator Calculator = vtkArrayCalculator.New();
if (bArrayIsVector)
{
    string Function = "iHat." + FeatureName + "+jHat." + FeatureName + "+kHat." + FeatureName;
    Calculator.SetInputData(DataSet);
    Calculator.AddVectorArrayName(FeatureName, 0, 1, 2);
    Calculator.SetFunction(Function);
    Calculator.SetResultArrayName(ResultDataArrayName);
    Calculator.Update();
}
else
{
    string Function = "iHat*" + FeatureName + "+jHat*" + FeatureName + "+kHat*" + FeatureName;
    Calculator.SetInputData(DataSet);
    Calculator.AddScalarArrayName(FeatureName, 0);
    Calculator.SetFunction(Function);
    Calculator.SetResultArrayName(ResultDataArrayName);
    Calculator.Update();
}

vtkPlaneSource planeSource = vtkPlaneSource.New();
[...]
planeSource.Update();

vtkStreamTracer StreamTracer = vtkStreamTracer.New();
StreamTracer.SetInputConnection(Calculator.GetOutputPort());
StreamTracer.SetSourceConnection(planeSource.GetOutputPort());
StreamTracer.SetIntegratorTypeToRungeKutta45();

StreamTracer.SetIntegrationDirectionToForward();
StreamTracer.SetComputeVorticity(true);
StreamTracer.SetMaximumPropagation(StreamlineLengthPropagation);
StreamTracer.SetInitialIntegrationStep(0.3);
//WARNING: Set FIELD_NAME() so it can be processed by vtkAlgorithm
vtkInformationVector inArrayVec = StreamTracer.GetInformation().Get(vtkAlgorithm.INPUT_ARRAYS_TO_PROCESS());

vtkInformation inArrayInfo = inArrayVec.GetInformationObject(0);
inArrayInfo.Set(vtkDataObject.FIELD_NAME(), ResultDataArrayName);

if (bArrayIsVector)
{
    inArrayInfo.Set(vtkDataObject.FIELD_NAME(), FeatureName);
}

StreamTracer.Update();

vtkPolyData MyData = StreamTracer.GetOutput();
StreamTracer.Update();
MyData.BuildCells();
MyData.BuildLinks(0);

vtkPointData PointDatas = MyData.GetPointData();

```