# Far-field projections using data not from monitor

Hi,

I am working on a problem where I use a method similar to this: https://kb.lumerical.com/en/ref_sim_obj_tfsf_custom.html (i.e. the differential method)

Using this method I can get E, H, P, etc for any frequency-domain monitor I like, where the field from the source is eliminated. However, I would like to use this data to generate a far-field projection (farfield3d or similar).

farfield3d only seems to work for actual monitors, preventing me from using the data sets acquired through the differential method for far-field projection.

Is there a way to generate a far-field projection using the field components E, H?

Thanks,
Tom

Dear @tom.siday.15

Farfield3d and similar commands require monitor name for far field projections. In your case, since you want the far field data for scattered light, you need to obtain far field data in two cases (with and without scatter) and then subtract them. Please take a look at the Tips box in the link you provided:

2: far field projection: Some times users want to get the far field properties using the custom TFSF method. If this is the case, users must add a proper analysis group such as the "scat_ff" in Mie scattering 3D . At the same time, the script inside the analysis group should be modified in order to output the fields instead of the intensity. Then in the script file usr_source_CTFSF_NA.lsf users can add scripts to get the far field projection in the reference simulation and the scatter simulation. Their difference is the scattered far fields and can be easily plotted as intensity.

Thanks

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Thank you. I must have missed that box!

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