Two options :  <br>
- None :  the line-by-line calculation will not be convolved. The transmission in this case has the initial (maximal) resolution and the two other parameters:
"sampling ratio" and  "resolution power" have no effect,<br>
- Gaussian : the line-by-line calculation will be convolved by a gaussian profile, which FWHM (Full Width Half Maximum) is defined by a
user-provided desired spectral resolution power, and the transmission is provided according to the required sampling (see below).