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Re: Fractional SHIFT [message #28352 is a reply to message #28348]

Mon, 03 December 2001 13:10

Ralf Flicker
Messages: 19
Registered: October 2001

Junior Member

trouble wrote:
>
> Hi,
>
> Does anyone have a method for doing non-integer shifts ? Interpolate
> doesn't wrap in the way SHIFT does and my hack (based on MOD) is a bit
> dodgy.
>
> To shift orig by 1.5 pixels:
>
> orig = FINDGEN(10)
>
> index = FINDGEN(10)
> delta = 1.5
> index2 = (index+delta) MOD 10
>
> new = INTERPOLATE(orig,index2,/GRID)
>
> PRINT,new
>
> 1.50000 2.50000 3.50000 4.50000 5.50000
> 6.50000
> 7.50000 8.50000 9.00000 0.500000
>
> The 2nd last element of new is wrong (should be 9.5).
>
> Does anyone know a robust way ?

If you had periodic arrays you could FFT, multiply by a complex
exponential, and FFT back. In your example above, I guess you
could make orig periodic by mirroring it across the origin. No
idea if this will work for you, but I sometimes use the FFT +
complex exponential rather than interpolating for shifting
arrays non-integer steps.

cheers
ralf

--
Ralf Flicker UIN : 65334076
Gemini Observatory http://www.gemini.edu/
670 N. A'Ohoku Pl. Tel : (808) 974-2569
Hilo 96720, HI, USA Fax : (808) 935-9235

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[Message index]

		Re: Fractional SHIFT By: the_cacc on Tue, 04 December 2001 05:34
		Re: Fractional SHIFT By: Mark Rivers on Mon, 03 December 2001 19:55
		Re: Fractional SHIFT By: tam on Mon, 03 December 2001 13:34
		Re: Fractional SHIFT By: Ralf Flicker on Mon, 03 December 2001 13:10

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