What does 'Compute additional best fit' do?

[[Ti...]]

When you do a pre-alignment, there is a box that is checked by default that says 'Computer additional best fit'

 

I thought a pre-alignment is doing a best fit, so what exactly does doing an 'additional' best fit do. If you turn it off and on, I only see a very small difference?

 

I'm playing around with Short-Normal-Long as some of our programs take a long time to calculate a pre-alignment in the long setting. I feel a normal or short does just as good of a job, and sometimes it orients a symmetrical part with one clocking feature better on short than long.

 

Thanks

[[Be...]]

Hi Tim,

the 'Prealignment' is an alignment function which contains internally two steps: 'Guessing' a starting transformation  from an arbitrary data constellation and validating this guess via a kind of fast (but not so accurate) 'Bestfit' approach. Usually you can improve your result if you add a 'Local Bestfit' afterwards (with the checkbox), which runs for you really a 'Local Bestfit' with estimated 'Maximum search distance'. Nevertheless, if you are going to add a further main alignment (e.g. RPS or Geometric alignment or ...)  and you are already satisfied with the 'pure' Prealignment result as starting alignment you can reduce the computation time via disabling the 'Local Bestfit' checkbox.

Regards,

Bernd