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Re: Drawing vector fields with New Graphics [message #85080 is a reply to message #85074]

Tue, 02 July 2013 07:31

Phillip Bitzer
Messages: 223
Registered: June 2006

Senior Member

This doesn't help with your immediate problem, but part of the reason v1 appears smaller is your axis scale. See what I mean with these two commands:

IDL> v1.yrange=[-1, 4]
IDL> v1.xrange=[-1, 4]

This is because of what (relative to the vector) the x,y locations refer to. The default is the middle of the arrow. (You could also try v1.data_location=0 / v2.data_location=0 to "see" the same thing.)

This note in the help scares me:
Note: The units for the U and V components are arbitrary, and are not related to the units of the X and Y coordinates. The VECTOR function will compute a default length scale and head size based upon the overall number of vectors and the average magnitude of the vectors. The LENGTH_SCALE and HEAD_SCALE properties may be used to change the default size.

Intuitively (at least to me), this should not be the behavior. Uv, Ux should mean *something* about the magnitude.

From my reading of this note, it looks like you could find the average magnitude of the vectors in v1, which sets the default scale, and then scale the others (v2, etc) accordingly relative to this value.

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[Message index]

		Drawing vector fields with New Graphics By: Gordon Farquharson on Mon, 01 July 2013 14:34
		Re: Drawing vector fields with New Graphics By: Phillip Bitzer on Tue, 02 July 2013 07:31
		Re: Drawing vector fields with New Graphics By: David Fanning on Tue, 02 July 2013 07:38
		Re: Drawing vector fields with New Graphics By: Gordon Farquharson on Tue, 02 July 2013 10:54
		Re: Drawing vector fields with New Graphics By: David Fanning on Tue, 02 July 2013 11:10
		Re: Drawing vector fields with New Graphics By: David Fanning on Tue, 02 July 2013 11:32
		Re: Drawing vector fields with New Graphics By: Phillip Bitzer on Tue, 02 July 2013 11:15
		Re: Drawing vector fields with New Graphics By: David Fanning on Tue, 02 July 2013 11:40
		Re: Drawing vector fields with New Graphics By: Gordon Farquharson on Tue, 02 July 2013 12:08
		Re: Drawing vector fields with New Graphics By: Mark Piper on Thu, 04 July 2013 13:20

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