# Re: I need some clarification on vectors resources

From: David Brown <dbrown_at_nyahnyahspammersnyahnyah>
Date: Mon Nov 07 2011 - 15:35:39 MST

Hi Ugo,
I am not quite sure I understand your question, but vcRefLengthF is not the "mean" of anything. Perhaps you are trying to say "what is its meaning?". By default, it is set, based on the density of the vectors, to the length in NDC coordinate space of the maximum magnitude vector. Other vectors are drawn proportionally to this length. In the default situation, the reference length is set to a small enough value that vectors do not overlap. If you have a dense vector field this means that the vectors become very tiny. You can increase this length by setting vcRefLengthF to a larger value. It is possible to find out the current length used in a plot using a "getvalues" call, which you can read about if you are interested. Basically it looks like:

getvalues plot ; "plot" is the id of a plot object such as returned by the gsn_vector function
"vcRefLengthF" : ref_len
end getvalues
print("ref len is " + ref_len)

By default, as I said above, vcRefLengthF specifies the length of the maximum magnitude vector, and vcRefMagnitudeF will have the maximum magnitude as its value. However, you can set another magnitude as the reference magnitude. If you set the reference magnitude resource, then it becomes the magnitude that is drawn using the reference length. It could be a value larger than any magnitude in the field. If you set it to a small value relative to the maximum magnitude in the field, vectors larger than the reference magnitude can become very long. You can discover the current reference magnitude using the same "getvalues" call as you use to find the reference length.

Hope this helps,
-dave

On Nov 5, 2011, at 1:55 PM, ugo merlini wrote:

> Hi,
>
> As the subjects I need some clarification on vectors resources
>
> vcRefLengthF is the lenght reference of the vetcor but vcRefLengthF is the mean of what? I use vectors to plot U e V component
>
> Also is for me not clear vcRefMagnitudeF resources
>
> Regards
>
> Ugo
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Received on Mon Nov 7 15:35:45 2011

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