filter 'Plot over line' gives nan values


I am working with a 2d Tecplot file with a .plt extension. I want a graph of parameters like velocity along a line. So I used the function “plot over line”, but I got no chart in return. When I look at the spreadsheet view of “plot over line”, there are Nan values for all parameters. Can you help me with this?

Say, I would like to plot U_Uj along a line with Point1 (0,0,0) and Point2 (25,0,0).

Thank you

Hi @Leo0806

Which version of ParaView are you using ? PlotOverLine on 2D data was recently fixed.


I took a look at your data, and it does not appear to be correct. Your data looks like it is supposed to define a volume; it has many of hexahedra. However, the Z component of the coordinates seem to be missing. The entire volume is squashed onto the x-y plane. Because all the hexahedra lie on a plane, they are degenerate and this is fouling up the intersection queries necessary for the Plot Over Line filter. Even if the intersection queries did work, the results could be problematic as at every point you have many flattened cells overlapping each other. Which one should the plotter choose?

The best solution would be to go back and check your data. It does not seem to be generated correctly. If having a volume flattened onto the x-y plane is really want you want (which makes little sense), you can get the Plot Over Line filter to work by running the Extract Surface filter. This will pull out some quadrilateral faces that will intersect with the line correctly.

Sorry for the late reply!

I actually tried opening the Tecplot file in Tecplot 360. It worked well, showing the correct 3D volume mesh. However, when I open it in Paraview, it seems to be mistaken and shows the 2D volume mesh squashed onto the x-y plane.

Is this a problem with Paravire reading the Tecplot file? If yes, is it possible to fix it? Thank you!

Hmm. This could be a problem with the reader.

This Tecplot reader is one of those in the VisitBridge, which means that the reader comes from the VisIt developer team. I just tried loading your data in the most recent version of VisIt (3.3.2) and got the same behavior. So, if it is an issue with the reader, it would at best take a long time for the fix to make it to ParaView. (See for example Issue with tecplot binary cell centered data. for a different problem with the same reader.)

That said, I took another look at your data, and it appears that the coordinates are repeated in the x_D, y_D and z_D fields, and the z_D field is actually correct. So, you can use the Calculator filter to fix the coordinates. Turn on the Coordinate Results checkbox and set the expression to coords + z_D*kHat.

After you fix the coordinates, you may need to change to 3D interaction in the view. Click the 2D in the small toolbar over the render view to change it to 3D.

Here is a state file that enacts this fix: fixed-coordinates.pvsm (299.5 KB)

Dear Kenneth,
Thank you so much! This indeed solves the issue.

Dear Kenneth,

I am very new to ParaView and not familiar with it. I am stuck with plotting on a plane. Say, I want to plot U_Uj * (d U_Uj / d x) on a rectangle, z=0, 1<x<2, 1<y<2. How could I do it?

Thank you!

This is a new question (actually 2 new questions), and that is usually best asked on a whole new thread. But I’ll answer them here.

The first question is how to derive U_Uj * (d U_Uj / d x), Your data has a U_Uj field. You can get the derivative in each direction by using the Gradient filter. You can then use the Calculator filter to multiple U_Uj with the x component of the gradient.

The second question is how to plot on a plane. You can do that in ParaView by using the Slice filter image. Click the Z Normal button and ensure the origin has the z component as 0 to slice along the z=0 plane.

That will give you the slice along the entire domain. You can zoom to the part you want, or you can use the Clip filter image. Change the
Clip Type to Box. Then change Position to 1, 1, -1 and Length to 2, 2, 2 to get the 1<x<2, 1<y<2, z=0 region. You probably also want to turn off Show Box.

Here is the state file I created with your data to do this: plane-plot.pvsm (853.6 KB)