| Re: Maximum Likelihood processing time [message #38421] |
Tue, 09 March 2004 08:39  |
btt
Messages: 345
Registered: December 2000
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Senior Member |
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Lorenzo Busetto wrote:
> Hi all,
>
> I need to evaluate the variation in the processing time required to
> perform a maximum likelihood classification with a variable number of
> input bands, so I'm using the ENVI built-in functions "envi stats
> doit" (in order to compute ROI statistics) and "class_doit" (in order
> to classify the image).
>
> My problem is that when I perform the classification for the first
> time I have a high processing time (i.e. 60 seconds), but if I perform
> the same classification a second time, the time required for the
> process is much lower (i.e. 10 seconds). I tried to reset the idl
> session (with the .FULL_RESET_SESSION command), and also to quit and
> restart idl and perform again the classification, but after the first
> classification the time required for the process remains low. The only
> way to have a comparable processing time is to restart my pc.
> This also happens if I increase the number of input bands used: If I
> make a classification with 10 bands, I have a high processing time,
> but if I first make a classification with 5 bands and then a
> classification with 10 bands, the time required for the 10 bands
> classification is lower.
>
> Does anybody know why it happens ? Is IDL (or ENVI) "storing"
> somewhere the informations on previous calculations ?
>
> I don't want to have to restart my computer every time I change the
> number of bands in order to get comparable processing times....
>
Hello,
I think what you are seeing is that when a routine is first called, IDL
has to search for it and (possibly) compile it. Subsequent calls don't
have to be compiled.
You could compile the routines before running the routine (see .compile)
or you could perform your comparisons only after the routine has been
called at least once.
Ben
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