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E.7 Post-processing module

  1. How do I compute a section of a plot?

    Use ‘Tools->Plugins->Cut Plane’.

  2. Can I save an isosurface to a file?

    Yes: first run ‘Tools->Plugins->Cut Map’ to extract the isosurface, then use ‘View->Save As’ to save the new view.

  3. Can Gmsh generate isovolumes?

    Yes, with the CutMap plugin (set the ExtractVolume option to -1 or 1 to extract the negative or positive levelset).

  4. How do I animate my plots?

    If the views contain multiple time steps, you can press the ‘play’ button at the bottom of the graphic window, or change the time step by hand in the view option panel. You can also use the left and right arrow keys on your keyboard to change the time step in all visible views in real time.

    If you want to loop through different views instead of time steps, you can use the ‘Loop through views instead of time steps’ option in the view option panel, or use the up and down arrow keys on your keyboard.

  5. How do I visualize a deformed mesh?

    Load a vector view containing the displacement field, and set ‘Vector display’ to ‘Displacement’ in ‘View->Options->Aspect’. If the displacement is too small (or too large), you can scale it with the ‘Displacement factor’ option. (Remember that you can drag the mouse in all numeric input fields to slide the value!)

    Another option is to use the ‘General transformation expressions’ (in View->Options->Offset) on a scalar view, with the displacement map selected as the data source.

  6. Can I visualize a field on a deformed mesh?

    Yes, there are several ways to do that.

    The easiest is to load two views: the first one containing a displacement field (a vector view that will be used to deform the mesh), and the second one containing the field you want to display (this view has to contain the same number of elements as the displacement view). You should then set ‘Vector display’ to ‘Displacement’ in the first view, as well as set ‘Data source’ to point to the second view. (You might want to make the second view invisible, too. If you want to amplify or decrease the amount of deformation, just modify the ‘Displacement factor’ option.)

    Another solution is to use the ‘General transformation expressions’ (in ‘View->Options->Offset’) on the field you want to display, with the displacement map selected as the data source.

    And yet another solution is to use the Warp plugin.

  7. Can I color the arrows representing a vector field with data from a scalar field?

    Yes: load both the vector and the scalar fields (the two views must have the same number of elements) and, in the vector field options, select the scalar view in ‘Data source’.

  8. Can I color isovalue surfaces with data from another scalar view?

    Yes, using either the CutMap plugin (with the ‘dView’ option) or the Evaluate plugin.

  9. Is there a way to save animations?

    You can save simple MPEG animations directly from the ‘File->Save As’ menu. For other formats you should write a script. Have a look at ‘tutorial/t8.geo’ or ‘demos/anim.script’ for some examples.

  10. Is there a way to visualize only certain components of vector/tensor fields?

    Yes, by using either the “Force field” options in ‘Tools->Options->View->Visibility’, or by using ‘Tools->Plugins->MathEval’.

  11. Can I do arithmetic operations on a view? Can I perform operations involving different views?

    Yes, with the Evaluate plugin.

  12. Some plugins seem to create empty views. What’s wrong?

    There can be several reasons:

    • the plugin might be written for specific element types only (for example, only for scalar triangles or tetrahedra). In that case, you should transform your view before running the plugin (you can use Plugin(DecomposeinSimplex) to transform all quads, hexas, prisms and pyramids into triangles and tetrahedra).
    • the plugin might expect a mesh while all you provide is a point cloud. In 2D, you can use Plugin(Triangulate) to transform a point cloud into a triangulated surface. In 3D you can use Plugin(Tetrahedralize).
    • the input parameters are out of range.

    In any case, you can automatically remove all empty views with ‘View->Remove->Empty Views’ in the GUI, or with Delete Empty Views; in a script.

  13. How can I see “inside” a complicated post-processing view?

    Use ‘Tools->Clipping Planes’.

    When viewing 3D scalar fields, you can also modify the colormap (‘Tools->Options->View->Map’) to make the iso-surfaces “transparent”: either by holding ‘Ctrl’ while dragging the mouse to draw the alpha channel by hand, or by using the ‘a’, ‘Ctrl+a’, ‘p’ and ‘Ctrl+p’ keyboard shortcuts.

    Yet another (destructive) option is to use the ExtractVolume option in the CutSphere or CutPlane plugins.

  14. I am loading a valid 3D scalar view but Gmsh does not display anything!

    If your dataset is constant per element make sure you don’t use the ‘Iso-values’ interval type in ‘Tools->Options->View->Range’.

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