Jon,

The relevant parameters are 'scale_units' (not 'units') and 'scale'. I

think the docstring entry for 'scale_units' will clarify the situation:

scale_units : [ 'width' | 'height' | 'dots' | 'inches' | 'x' | 'y' |

'xy' ], \

None, optional

If the *scale* kwarg is *None*, the arrow length unit. Default is

*None*.

e.g. *scale_units* is 'inches', *scale* is 2.0, and

``(u,v) = (1,0)``, then the vector will be 0.5 inches long.

If *scale_units* is 'width'/'height', then the vector will be half the

width/height of the axes.

If *scale_units* is 'x' then the vector will be 0.5 x-axis

units. To plot vectors in the x-y plane, with u and v having

the same units as x and y, use

``angles='xy', scale_units='xy', scale=1``.

In other words,

data_value * scale_units / scale = size in scale_units

I suspect it would have been less confusing if scale had been defined as

the reciprocal of what it is--but we are stuck with it as-is.

Eric

On 2018/03/01 10:53 AM, Slavin, Jonathan wrote:

> Hi,

>

> I'm making a plot in which I plot a bunch of velocity vectors that show

> the deviation of the material from it's average velocity. I use

> quiverkey to show the size scale of the vectors, but I'd also like to

> show the mean velocity vector on the plot.

> So, what I need is the meaning of the scale value. I'm using

> units='dots' and have set the scale value by trial and error to 0.75 to

> get a good looking plot. Given these, can someone tell me how to

> translate some value from a magnitude for a vector to a length on my

> plot? I've looked at the code for quiver and quiverkey and it's a bit

> opaque to me, at least without spending significant time studying it.

>

> Regards,

> Jon

>

> --

> ________________________________________________________

> Jonathan D. Slavin Harvard-Smithsonian CfA

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