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Re: What is like CONGRID, but averages on reduction? [message #5174 is a reply to message #5108]

Mon, 16 October 1995 00:00

thompson
Messages: 584
Registered: August 1991

Senior Member

grunes@news.nrl.navy.mil (Mitchell R Grunes) writes:

> In article <45gk07$ahc@post.gsfc.nasa.gov> thompson@orpheus.nascom.nasa.gov (William Thompson) writes:
>> ...I think this should do what you want...

> No. Your procedure truncates the edges. E.G., try
> a=intarr(9,9)
> a(8,8)=10
> print,reduce(a,2,2)

> You will get all 0's.

You are correct. However, the following counterexample will not produce all
zeros.

IDL> A=intarr(8,8)
IDL> A(7,7)=10
IDL> print,reduce(A,2)
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 2

(If A had been a floating point array, instead of an integer one, the nonzero
pixel would have been 2.5 instead of 2.)

The routine works by trimming off just enough of the edge so that the array
dimensions are then multiples of the reduction factor. For example, if one
wants to reduce a 1000x1000 array by three, then the first step is to trim off
the edge to make it a 999x999 array. I've always found this acceptable for
what I wanted to do, but I can understand if you do not.

Bill Thompson

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[Message index]

		What is like CONGRID, but averages on reduction? By: grunes on Tue, 10 October 1995 00:00
		Re: What is like CONGRID, but averages on reduction? By: thompson on Mon, 16 October 1995 00:00
		Re: What is like CONGRID, but averages on reduction? By: grunes on Thu, 12 October 1995 00:00
		Re: What is like CONGRID, but averages on reduction? By: thompson on Wed, 11 October 1995 00:00

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