| Re: Array Tiling - The IDL Way [message #79572] |
Mon, 12 March 2012 12:32  |
rogass
Messages: 200
Registered: April 2008
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Senior Member |
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On 12 Mrz., 19:54, Michael Galloy <mgal...@gmail.com> wrote:
> On 3/12/12 11:31 AM, Percy Pugwash wrote:
>
>> I have a large array that I'd like to break up into tiles (square tiles of side T). I would like to have those tiles in the form of a stack, such that my array goes from dimensions [Nx*T,Ny*T] to [T,T,Nx*Ny].
>
>> Is there any way I can do this using only functions like REFORM and TRANSPOSE and no for-loops? Ideally I'd like to do it in-place too. I've been racking my brain for a nice IDLesque way to do this, but no luck thus far...
>
>> P
>
> I think this is what you are trying to do:
>
> IDL> a = indgen(10, 10)
> IDL> b = transpose(reform(a, 2, 5, 2, 5), [1, 3, 0, 2])
>
> This will break the image a into 5 tiles of size 2 in each dimension. So
> you can do the following, e.g., to retrieve the tile at (4, 4):
>
> IDL> print, reform(b[4, 4, *, *])
> 88 89
> 98 99
>
> Mike
> --
> Michael Galloywww.michaelgalloy.com
> Modern IDL, A Guide to Learning IDL:http://modernidl.idldev.com
> Research Mathematician
> Tech-X Corporation
Uh, it's a 'little' bit more efficient than my one .... :)
Cheers
CR
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| Re: Array Tiling - The IDL Way [message #79573 is a reply to message #79572] |
Mon, 12 March 2012 12:28  |
rogass
Messages: 200
Registered: April 2008
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Senior Member |
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On 12 Mrz., 18:31, Percy Pugwash <percy.pugw...@gmail.com> wrote:
> I have a large array that I'd like to break up into tiles (square tiles of side T). I would like to have those tiles in the form of a stack, such that my array goes from dimensions [Nx*T,Ny*T] to [T,T,Nx*Ny].
>
> Is there any way I can do this using only functions like REFORM and TRANSPOSE and no for-loops? Ideally I'd like to do it in-place too. I've been racking my brain for a nice IDLesque way to do this, but no luck thus far...
>
> P
Hi,
just have a try with this. Note that your tile size must be an integer
part of the original image.
function cr_tile,im,wx,wy
s = size(im,/dim)
nel = n_elements(im)/(wx*wy)
ind = rebin((lindgen(wx,wy) mod wx) + $
rebin(lindgen(1,wy)*s[0],wx,wy,/sample),wx,wy,nel,/
sample)
ind += rebin(reform((lindgen(s))[0:*:wx,0:*:wy],1,1,nel,/
over),wx,wy,nel)
return,im[temporary(ind)]
end
Cheers
CR
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| Re: Array Tiling - The IDL Way [message #79574 is a reply to message #79573] |
Mon, 12 March 2012 11:54 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On 3/12/12 11:31 AM, Percy Pugwash wrote:
> I have a large array that I'd like to break up into tiles (square tiles of side T). I would like to have those tiles in the form of a stack, such that my array goes from dimensions [Nx*T,Ny*T] to [T,T,Nx*Ny].
>
> Is there any way I can do this using only functions like REFORM and TRANSPOSE and no for-loops? Ideally I'd like to do it in-place too. I've been racking my brain for a nice IDLesque way to do this, but no luck thus far...
>
> P
I think this is what you are trying to do:
IDL> a = indgen(10, 10)
IDL> b = transpose(reform(a, 2, 5, 2, 5), [1, 3, 0, 2])
This will break the image a into 5 tiles of size 2 in each dimension. So
you can do the following, e.g., to retrieve the tile at (4, 4):
IDL> print, reform(b[4, 4, *, *])
88 89
98 99
Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL, A Guide to Learning IDL: http://modernidl.idldev.com
Research Mathematician
Tech-X Corporation
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| Re: Array Tiling - The IDL Way [message #79628 is a reply to message #79574] |
Sat, 17 March 2012 09:13 |
Percy Pugwash
Messages: 12
Registered: January 2012
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Junior Member |
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Thanks for the suggestions.
Unfortunately in this case it seems that the nested for-loop method is actually much faster! I think the reason is that the arrays I'm using are so large (gigabytes in size) that the amount of memory manipulation involved in the TRANSPOSE operation dwarfs the time spend on running a for-loop.
Ah well.
P
On Monday, 12 March 2012 18:54:59 UTC, Mike Galloy wrote:
> On 3/12/12 11:31 AM, Percy Pugwash wrote:
>> I have a large array that I'd like to break up into tiles (square tiles of side T). I would like to have those tiles in the form of a stack, such that my array goes from dimensions [Nx*T,Ny*T] to [T,T,Nx*Ny].
>>
>> Is there any way I can do this using only functions like REFORM and TRANSPOSE and no for-loops? Ideally I'd like to do it in-place too. I've been racking my brain for a nice IDLesque way to do this, but no luck thus far...
>>
>> P
>
> I think this is what you are trying to do:
>
> IDL> a = indgen(10, 10)
> IDL> b = transpose(reform(a, 2, 5, 2, 5), [1, 3, 0, 2])
>
> This will break the image a into 5 tiles of size 2 in each dimension. So
> you can do the following, e.g., to retrieve the tile at (4, 4):
>
> IDL> print, reform(b[4, 4, *, *])
> 88 89
> 98 99
>
> Mike
> --
> Michael Galloy
> www.michaelgalloy.com
> Modern IDL, A Guide to Learning IDL: http://modernidl.idldev.com
> Research Mathematician
> Tech-X Corporation
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