input2;
input2->DeepCopy(image);
imageAppend->SetInputData(image);
imageAppend->AddInputData(input2);
imageAppend->SetAppendAxis(0);
imageAppend->Update();
output->ShallowCopy(imageAppend->GetOutput());
return 0;
}
```
In this snippet, I try to append the same ImageData twice. However, when executing with Paraview, if I look at the results in the spreadsheet view, I can clearly see that the data does not grow, and there are as many points after my filter as before, when the number of points should double.
I feel like I am missing a step, but I can’t seem to figure out what.
Is there some additional things to do to ensure the data is indeed created and passed down the pipeline?
Thanks for any help
---
### Author:  [@eve-le-guillou](https://discourse.paraview.org/u/eve-le-guillou)
#### Post date: [April 14, 2023, 3:58pm UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/2 "2023-04-14T15:58:27Z")
Hi all,
I have managed to eventually to append the data and show it in Paraview. What was missing was a new RequestInformation method like this:
```auto
int ttkperiodiqueGhostsGeneration::RequestInformation(
vtkInformation *ttkNotUsed(request),
vtkInformationVector **inputVectors,
vtkInformationVector *outputVector) {
vtkImageData* image = vtkImageData::GetData(inputVectors[0]);
vtkImageData *output = vtkImageData::GetData(outputVector);
int newExtent[6];
int* extent = image->GetExtent();
newExtent[0] = extent[0];
newExtent[1] = extent[1]+(extent[1]-extent[0]);
newExtent[2] = extent[2];
newExtent[3] = extent[3];
newExtent[4] = extent[4];
newExtent[5] = extent[5];
vtkInformation *outInfo = outputVector->GetInformationObject(0);
outInfo->Set(vtkStreamingDemandDrivenPipeline::UNRESTRICTED_UPDATE_EXTENT(), 1);
outInfo->Set(
vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT(), newExtent, 6);
return 1;
}
```
However, I still have an error message from Paraview:
```auto
( 14.760s) [paraview]vtkStreamingDemandDrive:867 ERR| vtkPVPostFilterExecutive (0x55890232eee0): The update extent specified in the information for output port 0 on algorithm vtkPVPostFilter (0x55890232be90) is -10 30 -10 10 -10 10, which is outside the whole extent -10 10 -10 10 -10 10.
```
I am doing something wrong?
Is there a way to move the code inside `RequestInformation` to `RequestData`?
Thanks for any help.
---
### Author:  [@nicolas.vuaille](https://discourse.paraview.org/u/nicolas.vuaille)
#### Post date: [April 17, 2023, 7:46am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/3 "2023-04-17T07:46:59Z")
@Charles_Gueunet maybe ?
---
### Author:  [@Charles\_Gueunet](https://discourse.paraview.org/u/Charles_Gueunet)
#### Post date: [April 17, 2023, 8:49am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/4 "2023-04-17T08:49:41Z")
I think you would need to be able to use the `vtkImageAppend::RequestInformation` on your own `RequestInformation`.
The easiest way to do so would be to set the `vtkImageAppend` filter as an internal field in your class so you can call its `RequestInformation` directly inside your own. You would also need to provide the `AppendAxis` directly in your constructor as it needs to be set before the pipeline call these methods.
---
### Author:  [@eve-le-guillou](https://discourse.paraview.org/u/eve-le-guillou)
#### Post date: [April 18, 2023, 9:18am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/5 "2023-04-18T09:18:24Z")
Hi,
Thanks for the reply. I will try this and get back to you if I have any problems.
---
### Author:  [@eve-le-guillou](https://discourse.paraview.org/u/eve-le-guillou)
#### Post date: [April 24, 2023, 10:30am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/6 "2023-04-24T10:30:51Z")
Hi,
Unfortunately, as the `RequestInformation` method in `vtkImageAppend` is protected, I can’t call it from my own filter.
Furthermore, my end goal is to use several `vtkImageAppend` filters, for which some of the data is not available before the execution of the filter, and some computation is also necessary to know how many `vtkAppendImage` filters are necessary and what their append axis are.
Is there a way to solve the problem showed by the error message from my filter’s `RequestData`?
Thanks for any help.
---
### Author:  [@Charles\_Gueunet](https://discourse.paraview.org/u/Charles_Gueunet)
#### Post date: [April 26, 2023, 9:09am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/7 "2023-04-26T09:09:13Z")
> Unfortunately, as the `RequestInformation` method in `vtkImageAppend` is protected, I can’t call it from my own filter.
I do not like when a filter does this… You have two ways to overcome this small issue:
1. The clean one, when you call `UpdateInformation()` of the `vtkImageAppend` filter then retrieve the Keys you need on your own `RequestInformation` (using `GetInformation`).
2. The easy one, when you create a dumb intermediate class, that inherits from `vtkImageAppend` and override the `Request*` methods in its `public` area.
> Furthermore, my end goal is to use several `vtkImageAppend` filters, for which some of the data is not available before the execution of the filter, and some computation is also necessary to know how many `vtkAppendImage` filters are necessary and what their append axis are.
From my understanding, as long as you are directly outputting `vtkImageData` you need to have a correct `WHOLE_EXTENT` at the end of the `RequestInformation`. As this is also true for the filters used in the input, I am not sure to get which information you would miss during this step to compute a valid one, as all your input ImageData should have their extent available.
> Is there a way to solve the problem showed by the error message from my filter’s `RequestData`?
The workaround I would see would be to output a `vtkPartitionnedDataSet` (or another composite) instead of an image data if you cannot fulfill the Whole extent constraint. This approach has some drawbacks of course as the input is now inside a composite.
---
### Author:  [@eve-le-guillou](https://discourse.paraview.org/u/eve-le-guillou)
#### Post date: [April 28, 2023, 9:38am UTC](https://discourse.paraview.org/t/create-filter-that-uses-vtkimageappend/11857/8 "2023-04-28T09:38:42Z")
Thank you for the reply.
I eventually created my own function for merging vtkImageData objects that corresponded to my needs better.
The error message mentioned earlier was due to my implementation missing the `RequestUpdateExtent` function, similarly to what is described [here](https://discourse.paraview.org/t/adding-new-points-in-programmable-filter/9383/3).
Everything seems to work well now.
Thanks for all the help!