Hello,
Something like (on windows)
mumax3-convert -vtk="ascii" filename.ovf
should work.
As Arindam mentioned, that error message is a path error. For example, if your mumax3-convert is located in C:\Mumax3\, but your data is in C:\Mumax3\Data, if you try to run the command while inside the Data folder, Windows won't be able to find the exe, and will give that error. You would need to be in the Mumax3 folder, and run it as
mumax3-convert -vtk="ascii" C:\Mumax3\Data\filename.ovf
Where, since we're in the Mumax3 folder, I am giving it the full path to the ovf (you can also do just \Data\filanename.ovf, since it's a subfolder of Mumax3). You can also give the full mumax3-convert path. So
C:\Mumax3\mumax3-convert -vtk="ascii" C:\Mumax3\Data\filename.ovf
This version should work regardless of what folders anything is in, because it's giving the full absolute paths to everything.
Or add mumax3-convert to the path variable. When adding to the path variable, make sure you add the folder, not the executable itself. So for example, if the full executable is C:\Mumax3\mumax3-convert.exe, you want to add just "C:\Mumax3" to the path. This will tell windows to look in "C:\Mumax3\" for the mumax3-convert executable, regardless of what folder you are currently in. (Also note, when adding it in windows, there are 2 PATHs- one under user variables, another under system variables. In case that matters)
Usually the .exe part is not needed, but you can also add that. So it'd be
C:\Mumax3\mumax3-convert.exe -vtk="ascii" C:\Mumax3\Data\filename.ovf
It shouldn't matter, but it doesn't hurt to have it
Best regards,
Josh L.