Generating view matrices for multiple glazing apertures in Radiance?

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While it is true that you can only have one sender object per rfluxmtx calculation, you can specify as many "receiver" objects as you like; in this case, all of the windows in a given room. The sender in this case is replaced by your selection of points, as is normal for a view matrix calculation. To include multiple receivers, you need to specify the output file ahead of each window's polygon using the

#@rfluxmtx o=output.mtx

variable as described in the man page https://radiance-online.org/learning/...

The view matrix calculation will also be more efficient if you can avoid running it separately for each window in this way.

While you did not ask, you do need to run rfluxmtx once per elevation (i.e., direction) to calculate the external "daylight" matrices connecting the building exterior to the sky, since the sky (+ground) is in this case the only receiver. Normally, this means running rfluxmtx once per window. A shortcut is possible when there are few nearby obstructions outside the building, and the windows all lie in a plane that you can assemble as a single "source" for that elevation, even though they may be physically separated by mullions or wall sections. Again, it will be more efficient to combine calculations in this way, but it is not required by the method.

The tutorial recommended by JChen remains the authoritative source.

Best, -Greg