| Re: ROI Scaling [message #55041] |
Tue, 31 July 2007 09:49  |
Dick Jackson
Messages: 347
Registered: August 1998
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Senior Member |
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"Erik" <janssen.e@gmail.com> wrote in message
news:1185887600.007960.156080@o61g2000hsh.googlegroups.com.. .
> Hi folks,
>
> I run into a small problem when scaling a IDLgrROI object. I want the
> ROI to stretch out so that it's slightly bigger. I'm using the SCALE
> function to achieve this:
>
> oRoi->Scale, [1.5,1.5]
>
> The scale function does what it promised; the ROI grows bigger.
> Unfortunately the position of the ROI gets messed up and the ROI moves
> upwards or even out of screen. Does someone know what causes this? I
> can't find more info or parameters in IDL's helpfile ;-)
The help file says "The IDLanROI::Scale procedure method modifies the vertices
for the region by applying a scale." To be more clear, that means that all your
X and Y values are scaled by simple multiplication. If your ROI were centered
around [0,0] it would work as (I think) you expect, and it would stay "in place"
and change in size.
To scale in place, try something like this:
;; Find 'centre' for scaling
oROI->GetProperty, ROI_XRange=xr, ROI_YRange=yr
midX = Mean(xr)
midY = Mean(yr)
;; Shift ROI to surround [0,0]
oROI->Translate, -midX, -midY
;; Scale ROI
oRoi->Scale, [1.5,1.5]
;; Shift ROI back
oROI->Translate, midX, midY
Hope this helps!
--
Cheers,
-Dick
--
Dick Jackson Software Consulting http://www.d-jackson.com
Victoria, BC, Canada +1-250-220-6117 dick@d-jackson.com
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