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Jeff Letendre jeff at bedrockdata.com
Wed Oct 19 14:13:41 CEST 2016 

On Oct 19, 2016 6:00 AM, <rrd-users-request at lists.oetiker.ch> wrote:

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> Today's Topics:
>
>    1. Re: rrdgraph: Negative values with --logarithmic (Christian Garbs)
>    2. Re: Confusion about VDEF total and graph values (humke)
>    3. Re: Confusion about VDEF total and graph values (humke)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 17 Oct 2016 20:25:37 +0200
> From: Christian Garbs <mitch at cgarbs.de>
> To: Alex van den Bogaerdt <alex at vandenbogaerdt.nl>
> Subject: Re: [rrd-users] rrdgraph: Negative values with --logarithmic
> Message-ID: <20161017182537.GA30035 at cgarbs.de>
> Content-Type: text/plain; charset=utf-8
>
> On Mon, Oct 17, 2016 at 03:01:11AM +0200, Alex van den Bogaerdt wrote:
> > > What I want to achieve (and what I think those other proponents also
> > > had in mind) is that I essentially have some of my data mirrored at
> > > the x-axis for better readability (don't draw two values on top of
> > > each other).
> > >
> > > For example I plot outgoing packets on my network as a positive values
> > > while I plot the incoming packets via CDEF:output=0,outputx,- as
> > > negative values.  So the outgoing rate is shown above the x-axis and
> > > the incoming rate below the x-axis.
> >
> > So, what you want to show is the outcome of a normal logaritmic function,
> > but mirrored. Instead of a new function...
>
> Basically, yes, but because of the y axis I think I need some special
> logic in rrdgraph (see below).
>
> > > To tame network spikes somewhat I want to change the graph mode to
> > > logarithmic.  This works for the positive values, but the negative
> > > values simply vanish.  I just want the same transormation that happens
> > > to the positive values applied 'mirrored' the the negative values.
> > >
> > > Think of something like a "display-logarithm" function defined like
> > > this:
> > >
> > >
> > > double disp_log(double y)
> > > {
> > >     if (y == 0) {
> > >             return 0;
> > >     } else if (y > 0) {
> > >             return log(y);
> > >     } else {
> > >             return -log(-y);
> > >     }
> > > }
> > >
> > >
> > > While "-log(-y)" might look weird in a mathematical context I think
> that
> > > it makes sense in describing "do the same as for positive values, only
> > > in the other direction".
> >
> > ... can't you just use CDEF:mirrored=logresult,-1,* ?
> > Or am I missing something ?
>
> This would indeed give me the correct results and would draw a correct
> graph, but the y axis grid would not be logarithmic:
>
> If I put the values "1000" and "-1000" into a CDEF using normal and
> 'mirrored' LOG, I'll graph the values "3" and "-3".  The y grid will
> propably autoscale to "-10 ? 10" and show my values as "3" and "-3"
> instead of "1000" and "-1000".
>
> When I use --logarithmic, the positive values are also LOGed, but the y
> axis will be scaled logarithmic as well, so the y axis will show
> "1000" (or "10e3" or "1k") next to the graph value.
>
> If I could get a logarithmic y axis without using --logarithmic (for
> both positive and negative values), using LOG in a CDEF would indeed
> be a solution.
>
> Regards
> Christian
> --
> ....Christian.Garbs....................................https
> ://www.cgarbs.de
>
> "Die Ber?hmtheit mancher Zeitgenossen h?ngt mit der Bl?dheit
>  der Bewunderer zusammen."                -- Heiner Geissler
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 19 Oct 2016 00:44:54 -0700 (MST)
> From: humke <arjan.hummel at gmail.com>
> To: rrd-users at lists.oetiker.ch
> Subject: Re: [rrd-users] Confusion about VDEF total and graph values
> Message-ID: <1476863094342-7583447.post at n2.nabble.com>
> Content-Type: text/plain; charset=us-ascii
>
> Alex van den Bogaerdt-5 wrote
> >> Alex van den Bogaerdt-5 wrote
> >>> You mean you want to see the same bars, only reduced in width? In other
> >>> words, get smaller bars with gaps inbetween?
> >>
> >> That would also work visually, but what I had in mind was not to reduce
> >> the
> >> width, but create the bars by separating them with vertical lines of the
> >> correct height.
> >
> > I have difficulty understanding what you describe here.
>
> This piece of paint art shows best what I mean. Just smaller bars as per
> your suggestion would also work. I understand we will still be showing
> rates, but if the graph visually looks different (more like a histogram)
> when we CDEF'd a rate, that would be a nice visual cue that we did
> something
> to the original data (* 3600 in my case). Of course, title and comment
> strings could also be used to inform the viewer.
>
> <http://rrd-mailinglists.937164.n2.nabble.com/file/
> n7583447/gas_withlines.gif>
>
> Arjan
>
>
>
>
> --
> View this message in context: http://rrd-mailinglists.
> 937164.n2.nabble.com/Confusion-about-VDEF-total-and-graph-values-
> tp7583425p7583447.html
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>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 19 Oct 2016 00:54:29 -0700 (MST)
> From: humke <arjan.hummel at gmail.com>
> To: rrd-users at lists.oetiker.ch
> Subject: Re: [rrd-users] Confusion about VDEF total and graph values
> Message-ID: <1476863669285-7583448.post at n2.nabble.com>
> Content-Type: text/plain; charset=us-ascii
>
> Simon Hobson-2 wrote
> > I interpret him as : think about drawing each column in the graph as a
> box
> > with a thin (I guess 1 pixel is the minimum) outline round it in a
> > contrasting colour - but don't draw the top or bottom lines. You've now
> > got vertical lines separating the filled area.
> >
> > It's slightly more subtle, you actually want to only draw a line on
> either
> > the right, or the left, of each column - otherwise the side lines from
> two
> > adjacent columns combine to form a 2 pixel wide line.
> >
> > It also won't work if the columns are only 1 pixel wide.
>
> Almost... See my other post of today for a picture of what I mean.
>
> RRDgraph allows us to draw with pixels < 1 in size (I actually use 0.8 in
> my
> graphs). There's no such thing as half (or <1) a pixel in reality, but the
> rendering process uses the number to do some special 'smoothing' (there's a
> better term that won't pop up in my head) to make it visually look like a
> thinner line. I am not sure if it would help to give the desired effect in
> this case. If we could even generate the vertical lines that is which I so
> much desire ;)
>
>
>
>
>
> --
> View this message in context: http://rrd-mailinglists.
> 937164.n2.nabble.com/Confusion-about-VDEF-total-and-graph-values-
> tp7583425p7583448.html
> Sent from the RRDtool Users Mailinglist mailing list archive at Nabble.com.
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