[rrd-users] Re: negative & positive fill

Iain Buchanan iain at pcorp.com.au
Mon Apr 7 06:25:38 MEST 2003

I'm graphing data that has many too elements to display sensibly by
graphing them all.  Therefore I'm shading between min & max, and
graphing the average over the top.  Actually, I'm using AREA to graph
from 0 - max in grey, then another area to graph from 0 - min in white,
but the effect is the same.
There is an example here:

This is fine for data thats positive.  Recently I fixed a bug that
ignored all negative data (after all, its not a number if it doesn't
start with 0-9 right? :) and added some new trends that are legitimately
mostly negative.  The problem being AREA fills between 0 and value... 
It seems that my minimum shade is 'overwriting' the maximum (for
negative values), and I'm getting weird results:


Can anyone suggest a 'simple' way of overcoming this that would work for
data that is both positive and negative? The only way I can think of is
using another CDEF and doing another (shudder) RPN to test the value for
its sign, and then draw max or min first depending on the outcome... 
Maybe I could use AREA.

This is (roughly) the commands that create the graphs:

DEF:d2Fed2Pact=../rrd/test.rrd:Fed2Pact:MAX AREA:d2Fed2Pact#cccccc
DEF:d3Fed2Pact=../rrd/test.rrd:Fed2Pact:MIN AREA:d3Fed2Pact#ffffff

Many many thanks in advance!
Iain Buchanan <iain at nospam.pcorp.com.au>
"You are welcome to your opinion. I've got this great bridge to sell you too."

	- Alan Cox to someone recommending the NVidia drivers

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