| Re: Solve memory problems [message #64679 is a reply to message #64623] |
Wed, 14 January 2009 06:53   |
Jean H.
Messages: 472
Registered: July 2006
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Senior Member |
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Corinne,
setting var=0 or *ptr_var = 0 will have the same effect on memory.
Now, let's say you have 10 bands, 4000*5000. If you try to create an
array like this data = bytarr(4000,5000,10), you might run out of
memory, or, for the same reason, can not create any other variable (not
enough contiguous space in memory). With this example, you would need
about 8 bits * 4000 * 5000 * 10 = 1 600 000 000 bits of contiguous
memory. Now, if you use points, you can create an array of 10 pointers,
each holding a band.
ptr_data = ptrarr(10)
ptr_data[0] = ptr_new(bytarr(4000,5000)
ptr_data[1] = ptr_new(bytarr(4000,5000)
....
so now, the contiguous memory you need is only 8 bits * 4000 * 5000 =
160 000 000 bits.
If band 2 has a different size, no problem:
ptr_data[2] = ptr_new(bytarr(12,25)
Jean
Corinne wrote:
> hi jean,
>
> i have never used pointers, so my question is: do you use separate
> pointers or whole pointer-arrays for your bands? what do you do, if
> your bands have different sizes due to different spatial resolutions
> (which you might interpolate later in the programme)?
>
> i'm still trying to figure out, what the advantage of pointers is.
>
> example: i have created an float array a with 4000x5000 elements and
> don't need it anymore. so i want to get rid of it. does it make a
> difference, if i put a=0 or if i set the value of the pointer of the
> array to zero?
>
> regards,
> corinne
>
>
>> In my own program, I do all the analysis on a modified version of my
>> original image (a classified land-use map, with the background values
>> removed so the data is a 1D array), then, at the very end, I
>> re-transform it to save and display it. I save a lot of memory!
>> Moreover, all bands are saved in pointers, allowing the program to run
>> on almost any computer, while the original version, which did not use
>> much pointer, was making my work-beast run out of memory fairly quickly!
>>
>> Jean
>
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