Dear all, I have run a 3DH1 simulation and I need to set all Fourier coefficients to zero except those corresponding to a fundamental wavelength and its harmonics (e.g. keep only modes 0, +-5, +-10, etc and set all the rest to zero). I have the intuition that some combination of FieldConvert options can accomplish exactly this, but I am unsure of what is the best (or some) way to proceed. My guess is that the "homplane:wavespace:planeid=?" can be used to extract the individual Fourier modes, but I am unsure as to how the Fourier modes are sorted and which ones must be extracted to recover a chosen fundamental wavelength and its harmonics (both real and imaginary parts, or modulus and argument, or however the Fourier modes are stored). The only one I'm pretty sure of is mode 0 or mean mode. Once I get the individual fld files for each one of the modes, I was intending to use the "addfld:fromfld=mode1.fld:scale=1 mode1.xml mode2.fld newfile.fld" sequentially to build a solution from the chosen modes. The issue here is that the fields extracted with "homplane" seem to be 2D and would therefore need to be recast in 3DH1 form before proceeding to "addfld". How can this be done? Thanks in advance for your help Fer Mellibovksy