[rrd-users] Re: Y-axis values in CDEF?

Alex van den Bogaerdt alex at ergens.op.het.net
Wed Oct 5 12:09:36 MEST 2005

On Wed, Oct 05, 2005 at 09:42:00AM +0200, Frederik Teerlinck wrote:
> I'm making an RRDgraph and I'd like to have a stacked area from a fixed
> amount of pixels (in fact I have an invisible area with a fixed
> size stack area on top wich gives me a kind of figure with blocks).
> The problem is that I'm using the same script for different kind of
> RRDs and the range of the values is of a completely different
>  magnitude. Now as far as I know you can't give a fixed amount of
> pixels, only a fixed value, but of course if I have a fixed size of
> eg. 10, the size of the blocks will be totally different in a graph with
>  values around 1000 compared to a graph with values around 10. So then my idea
> was to use the min and max values of the Y axis and use this in a CDEF or VDEF
>  calculation (maxY-minY/50 will result in the same size for any kind
>  of RRD). A long explanation to finally come to my question: is it
> possible to use the min and max Y axis values in a CDEF? and if so, how?

No, not yet.  But you can have MIN and MAX from the data, almost as good.
If you are setting upper-limit or lower-limit, you could have a CDEF doing
some maths (if max(data) > upper_limit then use max(data) else upper-limit).

Doing more complex calculations is not yet possible in VDEFs so you will
need to use a CDEF for that.  If you do not want data from a DEF in your
CDEF, use POP to get rid of it.

Alex van den Bogaerdt

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