GNU mesh plot Q & A

[DanBrox]

Q: Trying to follow the SPECFEM2D user guide to visualize the mesh created by xmeshfem2D. On page 13, the user guide suggests:

within gnuplot, type ‘plot "OUTPUT_FILES/gridfile.gnu" w l’

but there is no gridfile.gnu file in the OUTPUT_FILES directory created by executing the ./bin/xmeshfem2D command, just a Database00000.bin file. Possible to instruct on how the mesh specified by Database00000.bin can be visualized?

A:the gridfile gets produced when you turn on this setting in Par_file:
..
output_grid_Gnuplot = .true. # generate a GNUPLOT file containing the grid, and a script to plot it
..

and the xmeshfem2D tool only is able to create the file if the mesh is not coming from external mesh files (read_external_mesh = .false.).

if the above won’t work for you, a quick way of looking at the mesh is also to turn on the postscript output and run a simulation to produce a few snapshots:
..
output_postscript_snapshot = .true. # output Postscript snapshot of the results every NTSTEP_BETWEEN_OUTPUT_IMAGES time steps or not
..
meshvect = .true. # display mesh on PostScript plots or not
..

btw, the Database***.bin files are storing everything for the solver, not just mesh infos, but all kinds of additional variables, so it is usually tricky to get something specific like a mesh or velocity model out of there. more often, we use the SAVE_MODEL = gll setting to store the model velocities in a binary format and then visualize those, e.g., with a script like utils/Visualization/plot_model_from_gll_or_binary_file.py. that’s helpful when doing FWI and updating model velocities.