How to retrieve data from NSDD operand

  • 2 December 2021
  • 2 replies

Hello! I am trying to retrieve the standard deviation value from a detector viewer via the use of a NSDD operand #Pix -4 . How might I do so? 



Best answer by David.Nguyen 2 December 2021, 12:54

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Hi Kai,


The Help File about NSDD can be found under The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Merit Function Editor (automatic optimization group) > Optimization Operands by Category > Non-sequential Ray Tracing and Detector Operands.

In short, prior to calling any subsequent NSDD operand, you need a call to a NSDD which clears all detectors. Since all detectors need to be cleared, you also need to run a raytrace. In your Merit Function you should have:

  1. NSDD to clear all detectors
  2. NSTR to run a raytrace
  3. NSDD to retrive detector values/metrics

I’ve shown an example in the screenshot below:

For the standard deviation you need to specify the Det#, 2 in my case, the Pix#, -4 as you mentioned, and the Data is 0 for flux, 1 for flux/area, 2 for flux/solid angle pixel, 3 for normalized flux, 4 for absorbed flux, and 5 for absorbed flux/area.

Does that make sense?

Take care,



Hello David, thanks for helping me out once again!