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Re: Beginner Question: PlotS rasterization info? [message #27806 is a reply to message #27800]

Wed, 07 November 2001 09:10

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Ted (sehgal@oasis.rad.upenn.edu) writes:

> When PlotS or Plot rasterizes straight lines between endpoints/vertices,
> what's the best way to get the coordinates of all the points
> interpolated? Surely this information is stored somewhere. Can I get
> these coordinates without actually plotting anything to the screen? I
> tried a Bresenham algorithm, but it doesn't return exactly the same
> interpolated points as PlotS--there appears to be some sort of roundoff
> difference. Any help would be appreciated, since currently I'm
> resorting to the roundabout and no doubt inefficient method of plotting
> to a pixmap, TVRD-ing, and then WHERE-ing the screen-dumped array....

Given the points (x1,y1) and (x2,y2), I think something like
this should work:

nPoints = ABS(x2-x1+1) > ABS(y2-y1+1)
xloc = x1 + (x2 - x1) * Findgen(nPoints) / (nPoints - 1)
yloc = y1 + (y2 - y1) * Findgen(nPoints) / (nPoints - 1)

You might have to ROUND the locations, but this should get
you pretty close, I think.

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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[Message index]

		Re: Beginner Question: PlotS rasterization info? By: David Fanning on Wed, 07 November 2001 15:18
		Re: Beginner Question: PlotS rasterization info? By: sandy on Wed, 07 November 2001 14:20
		Re: Beginner Question: PlotS rasterization info? By: Craig Markwardt on Wed, 07 November 2001 11:03
		Re: Beginner Question: PlotS rasterization info? By: David Fanning on Wed, 07 November 2001 09:10

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