[Paraview] [EXTERNAL] Delaunay 2D question

[Moreland, Kenneth]

The problem you have is that you have no way to define what the outer boundaries of the shape are. As a human looking at the shape, I can reasonably guess that the space in the middle bottom of the data is supposed to be empty. But even then I'm not totally sure where the boundary is. I don't think there is any reasonable way a filter can predict where there is or isn't supposed to be data. The Delaunay filter makes the reasonable (but often wrong) assumption that mesh should cover the convex hull. However, the convex hull is conservative in that the result will always cover the space that should be covered plus some extra. So perhaps the easiest thing to do is remove the extra. I can think of three possible ways to do this.

First, you mentioned that you have a CFD solver. I presume that means you have a proper mesh for the CFD solver. Bring in that mesh and then run the Resample With Dataset filter with the results of the Delaunay2D as the Input and the CFD mesh as the Source. This will give you the CFD grid with the experimental values interpolated on the points.

The second thing you could try is to remove "bad" triangles. In you image I notice that most if not all of the polygons in the "empty space" region are either unusually large or unusually thin. You can use the Mesh Quality filter to get the area and aspect ratio of the triangles and then use the threshold filter to remove the triangles that are unusually large or thin.

The third thing you could try is to simply use the extract selection filter to get the cells you want. Use the "Select Cells On" tool to select the empty region of the data, then invert the selection, then run the Extract Selection filter.

I hope that helps.

-Ken

From: Neil Ashton <neil.ashton at manchester.ac.uk<mailto:neil.ashton at manchester.ac.uk>>
Date: Wednesday, November 6, 2013 7:24 AM
To: "paraview at paraview.org<mailto:paraview at paraview.org>" <paraview at paraview.org<mailto:paraview at paraview.org>>
Subject: [EXTERNAL] [Paraview] Delaunay 2D question

Hi all,

I have a query regarding the optimal way of visualising some point data from an experiment & CFD.

I have several 2D PIV windows from an experiment which have between 100 and 800 points arranged at several x and y locations. In order to compare these against CFD simulations I output the data from the same points in the CFD solver.

To visualise them I currently use the CSV reader, table to points, and then the Delaunay2D filters to turn this data into 2D slices.

The problem I have is when I have a gap in the data i.e the shape is not a square but has an empty bit in the middle. The Delaunay 2D filter triangulates all the data and it therefore doesn't constrain to the boundaries of the data.

I have attached three files which hopefully illustrate my problem.

I wanted to ask if there is a way to constrain the Delaunay2D filter or use an alternative method to ensure that the shape of the PIV/data window is preserved. I'm sure this type of thing is done fairly regularly but I couldn't figure out how to do this in Paraview.

Many thanks,

Neil

[cid:3D9195D7-F2E8-491F-9DF8-01FCD09C213C at telpol.net.pl][cid:D1DE831F-C375-42C8-A89B-DC7256042F36 at telpol.net.pl][cid:5E61420C-D394-4582-8178-5C4D62B1F8E5 at telpol.net.pl]
Dr Neil Ashton MEng (hons), PhD CEng MIMechE

Research Engineer

Computational Fluid Dynamics Group
School of Mechanical, Aerospace and Civil Engineering
University of Manchester
Manchester
M60 1QD
UK





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