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Re: Interpolation [message #59877 is a reply to message #2184]

Mon, 14 April 2008 08:34

Spon
Messages: 178
Registered: September 2007

Senior Member

On Apr 13, 1:56 am, tarequea...@gmail.com wrote:
> Step one: Real data in a XY frame
> Step two: 'Design a new xy frame, say X'Y' frame, whose values are
> generated from a chosen r_vec and theta_vec.
> Step 3: Now interpolate from XY to X'Y'.
>
> Tareque

Hi Tareque,

I'm guessing you know whereabouts your small frame is, within your big
frame, right?
So, if you take your big normal (x'y') frame, your small frame can be
defined by two points,
bottom-left and top-right - let's call them (b,l) & (t,r) - in terms
of x'y' grid co-oords.

-----
; Once you've worked out where these two points are, you can use
CONGRID on your xy dataset:
tempx = r - l ; How many data points of the x'y' grid does the xy grid
span
tempy = t - b ; in each dimension?

; interpolate to new sub-grid
newdata = congrid(data, tempx, tempy)

; Your x'y' frame co-ordinates for this data are
newx = l + lindgen(tempx)
newy = b + lindgen(tempy)

; (this bit is just array juggling to avoid for loops)
newx = rebin(newx,tempx,tempy)
newy = rebin(reform(newy,1,tempy),tempx,tempy)
newx = reform(newx,n_elements(newx))
newy = reform(newy,n_elements(newy))

; x'y' co-ordinates for ever datapoint in 'newdata'
xycoords = transpose([[newx],[newy]])

; so your new data should be at r/theta co-ordinates defined by:
polarcoords = cv_coord(from_rect = xycoords, /to_polar)
-----

I've assumed that your big circle is centered on the origin.
I've also assumed your small circle is in the upper-right quadrant of
your large circle here,
so I don't have to wrap my mind around minus-signs and the like...

I hope this helps and that I've understood your question
correctly. :-)

Regards,
Chris

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[Message index]

		Interpolation By: jun on Thu, 02 June 1994 10:44
		Re: Interpolation By: stl on Fri, 03 June 1994 01:14
		Re: Interpolation By: tarequeaziz on Mon, 14 April 2008 13:13
		Re: Interpolation By: Spon on Mon, 14 April 2008 11:44
		Re: Interpolation By: Spon on Mon, 14 April 2008 08:34
		Re: Interpolation By: tarequeaziz on Sat, 12 April 2008 17:56
		Re: Interpolation By: ben.bighair on Sat, 12 April 2008 15:26
		Re: Interpolation By: tarequeaziz on Sat, 12 April 2008 13:24
		Re: Interpolation By: ben.bighair on Sat, 12 April 2008 08:57
		Re: interpolation By: Yngvar Larsen on Thu, 08 December 2011 13:24
		Re: interpolation By: Brian Wolven on Thu, 08 December 2011 12:57
		Re: interpolation By: anil on Thu, 08 December 2011 04:15
		Re: interpolation By: anil on Thu, 08 December 2011 04:15
		Re: interpolation By: anil on Thu, 08 December 2011 04:15
		Re: interpolation By: Kenneth P. Bowman on Wed, 07 December 2011 14:25
		Re: interpolation By: Brian Wolven on Wed, 07 December 2011 12:27
		Re: interpolation By: David Fanning on Wed, 07 December 2011 12:13
		Re: interpolation By: Jeremy Bailin on Wed, 07 December 2011 12:07
		Re: interpolation By: anil on Wed, 07 December 2011 09:50
		Re: interpolation By: Russell[1] on Wed, 07 December 2011 08:42
		Re: interpolation By: anil on Wed, 07 December 2011 05:51
		Re: interpolation By: anil on Wed, 07 December 2011 05:48

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