[Radiance-general] Re: rtrace

[Thomas Bleicher]

On Wed, Jul 14, 2010 at 3:33 AM, Jia Hu <hujia06 at gmail.com> wrote:
> In the post
> http://www.rumblestrip.org/interests/light/rtrace-multiprocessing-option-initial-test-results/ and
> the rtrace manual page, both mentioned "-x" and "-n", What is the
> relationship between "-x" and "-n"?

"-n" simply defines how many processes are used for the calculation. I
think it starts a new process for each new input line. Therefore "-n"
should have no effect if you only have a single point to calculate.
Greg, please correct me if I'm wrong here.

"-x" harks back to the origins or Radiance and more or less defines
when rtrace should print out a batch of calculated results. Imagine
you have a grid of 1000 points and you set "-x" to 50 then your output
would be printed to the screen (or a file) in 20 chunks of 50 values.

I once set "-x" to 1 to have each new point printed and save to my
output file as soon as it was calculated (mostly to get feedback on
the calculation progress). However, that seemed to increase my
rendering time so I dumped that very quickly and reverted to feeding
smaller chucks of coordinates to rtrace instead.

I have to speculate about the connection between "-x" and "-n" here
but i think that if you allow more processes (-n) than points in a
scan line (-x) then rtrace simply can't start enough processes. This
would mean that each point creates it's own process. Greg?


Thomas