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Re: Speed penalty using START and COUNT with HDF_SD_GETDATA [message #26537 is a reply to message #26494]

Sat, 08 September 2001 08:29

Bob Fugate
Messages: 18
Registered: March 2001

Junior Member

> One strategy you might consider is
>
> data = fltarr(32,32,8000)
> for i=0,7999 do begin
> hdf_sd_getdata,arrayid, frame, start=[0,0,i], count=[128,128,1]
> data[*,*,i] = frame[46:77,43:74,0]
> endfor
>
> The motivation for this is that reading data along the final dimension is
> slow in any case (for reasons explained by Reimar) so the loop won't hurt
> you too much. By reading a full frame of data on each step you are reading
> contiguous data, which is fast. And by looping you avoid having to store
> large amounts of unneeded data.
>
> But test it for yourself!
>
> ---
> Mark Hadfield
> m.hadfield@niwa.cri.nz http://katipo.niwa.cri.nz/~hadfield
> National Institute for Water and Atmospheric Research

Thanks to Mark and Reimar for the suggestions. The SDS's are definitely
dimensioned, so I am not sub-sampling an array having dimensions=[0]. I
have settled on reading the entire 128x128 array and then extracting the
part I need. It turns out that I have enough RAM to read the entire 8000
frames without using a loop as you suggest above, Mark, so the whole
operation is fast.
Thanks again for your help.

Bob

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[Message index]

		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: Mark Hadfield on Wed, 05 September 2001 17:29
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: Mark Hadfield on Wed, 05 September 2001 17:19
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: R.Bauer on Wed, 05 September 2001 08:44
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: Bob Fugate on Wed, 05 September 2001 04:13
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: R.Bauer on Wed, 05 September 2001 00:35
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: Mark Hadfield on Tue, 04 September 2001 22:52
		Re: Speed penalty using START and COUNT with HDF_SD_GETDATA By: Bob Fugate on Sat, 08 September 2001 08:29

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