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Re: Image warping in IDL [message #51529 is a reply to message #51188]

Wed, 22 November 2006 00:21

Wox
Messages: 184
Registered: August 2006

Senior Member

On Tue, 21 Nov 2006 10:10:57 -0700, JD Smith <jdsmith@as.arizona.edu>
wrote:

> Interesting method. What I was specificially referring to is that you
> have no "sign" term for dx or dy, so I'm not sure how you know which
> quadrant relative to the target pixel your 4 output pixels occupy (UL,
> UR, LL, LR). It seems you're always hitting a single quadrant.

It's because I use [0,0] instead of [0.5, 0.5] as center of the first
pixel. floor(xy) gives then the lower-left pixel. So UR, UL, LR and LL
are given by:
floor(x)+offx[1,0,1,0]
floor(y)+offy[1,1,0,0]

As a consequence:
dxy=xy-floor(xy)
i.e. without the 0.5, so never negative.

The result will be shifted [0.5,0.5] with your "first-pixel"
definition. I guess if one keeps this definition in further
pixel-coordinate related operations, this isn't a problem.

> For the
> final fsum eq 0. test for empty pix, a simple where(fsum eq 0.) should
> suffice.

I got carried away by the histograms there ;-).

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[Message index]

		Image warping in IDL By: Wox on Wed, 08 November 2006 04:53
		Re: Image warping in IDL By: David Fanning on Fri, 10 November 2006 15:11
		Re: Image warping in IDL By: JD Smith on Fri, 10 November 2006 14:51
		Re: Image warping in IDL By: Wox on Tue, 14 November 2006 02:20
		Re: Image warping in IDL By: JD Smith on Mon, 20 November 2006 12:17
		Re: Image warping in IDL By: James Kuyper on Fri, 10 November 2006 08:38
		Re: Image warping in IDL By: Wox on Fri, 10 November 2006 01:12
		Re: Image warping in IDL By: Wox on Fri, 10 November 2006 01:05
		Re: Image warping in IDL By: JD Smith on Thu, 09 November 2006 11:50
		Re: Image warping in IDL By: Wox on Wed, 15 November 2006 04:18
		Re: Image warping in IDL By: Wox on Tue, 14 November 2006 08:20
		Re: Image warping in IDL By: Wox on Tue, 21 November 2006 01:18
		Re: Image warping in IDL By: JD Smith on Tue, 21 November 2006 09:10
		Re: Image warping in IDL By: Jeff Hester on Mon, 20 November 2006 09:00
		Re: Image warping in IDL By: Wox on Mon, 20 November 2006 01:18
		Re: Image warping in IDL By: JD Smith on Wed, 22 November 2006 08:22
		Re: Image warping in IDL By: Wox on Wed, 22 November 2006 00:21

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