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Old   July 9, 2012, 08:10
Question subtracting data from different slices
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Lydia Schulze
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Hello paraviewers!

For finding out the pressure difference in different heights in my model I would like to subtract the data of different slices from each other in my geometry. The slices have slightly different shapes.

Can anyone give my a hint how I can do that with paraview?
Your help is much appreciated !

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Old   July 5, 2016, 09:32
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Marc Vogel
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Hey paraviewers! Hey Lydia!
I would like to do something similar, but different models at same slice position.
Do you or anybody else knows the answer?

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Old   July 15, 2016, 13:15
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Hi Marc and Lydia,

This can be achieved in a couple of different ways, depending of what result you are looking for to compute. You can compute a visual scalar difference on the slice with a delta value, or just compute a number of the pressure difference that you are searching.

The later is more simple and if I understand you right is this what you are looking for. Below i give a brief explanation on the setup.

Start with making the two slices that you want to compare (e.g. inlet outlet).

Now you need to compute the average pressure on the slice. As far as I know is there at the moment no good function for this, but you can combine the following filters to achieve this (remember to use good naming of the calculator results to be able to distinguish them from each other).
1. Apply a calculator filter on the slice and compute the quantity of interest.
2. Add a "Integrate Variables" filter to the calculator (this value is integrated over area and needs to be divided by the area to gain the average).
3. Add a "CellDataToPointData" filter to the "Integrate Variables" filter (tic the "Pass Cell Data" box, this will enable you to divide the calculated value with the Area of the surface).
4. Add a Calculator filter where you can find your values of interest under "Scalars" and divide the two with each other to get the average quantity.

Perform the same routine for the second slice to get the second average value for the delta calculation.

Now you can group your last two calculators with the quantities that you want to use in the delta calculation by selecting them and adding the "Group Dataset" filter.

On this "Group Dataset" filter you can add the last calculator filter to compute the delta with your scalars.

Hope that this will work for you!

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difference, slices, subtraction

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