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Rounding errors and the New Graphics image routine [message #86040]

Wed, 25 September 2013 12:42

Gordon Farquharson
Messages: 48
Registered: December 2010

Member

Hi All

I'm posting this message as a reference, primarily for myself, in case I ever again find myself beating my head against the wall for several hours.

IDL> a = findgen(350,332)
IDL> x = 2000. * findgen(350) / 350.
IDL> y = 2000. * findgen(332) / 332.
IDL> p = image(a, x, y, AXIS_STYLE=2)
% Loaded DLM: PNG.

Everything is fine in IDL land so far...

IDL> x = 2000. * findgen(350) / 350. + 2.8e5
IDL> y = 2000. * findgen(332) / 332. + 3.8e6
IDL> p = image(a, x, y, AXIS_STYLE=2)
% Loaded DLM: QHULL.
% QHULL: Vector must have 350 elements: YIN
% Execution halted at: $MAIN$

WTF!

Several hours later (and many more expletives):

IDL> x = 2000. * findgen(350) / 350. + 2.8D5
IDL> y = 2000. * findgen(332) / 332. + 3.8D6
IDL> p = image(a, x, y, AXIS_STYLE=2)
IDL> p = image(a, x/1000., y/1000., AXIS_STYLE=2)

I guess I should have realized sooner that the problem would be due to a rounding error. Maybe this post will help somebody else out.

Gordon

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[Message index]

		Rounding errors and the New Graphics image routine By: Gordon Farquharson on Wed, 25 September 2013 12:42
		Re: Rounding errors and the New Graphics image routine By: robseigel on Thu, 28 November 2013 05:22

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