Re: [Gnuplot-info] logscale and autoscale improvement (was logscale and manual range setting?)

[James R. V. Z. <jr...@co...>]

Hans-Bernhard Broeker <br...@ph...> wrote:
>> How hard do you think it would be to start/end the axis
>> on a minitic rather than a major tic if too large a
>> fraction of the range is wasted?
> 
> Starting the axis on a minitic is IMHO not the right solution.
> Lifting the limitation that in log axes only at integer powers of
> the base can currently be major tics is what really needs tackling.
> While at it, other axis re-mappings than pow()/log() should be made
> possible.
> 
> Unfortunately, that'd end up in having to essentially re-write the
> entire autoticking stuff from scratch.  James Van Zandt made a
> proposal for that a long time ago, but it never made it into serious
> discussion, let alone the CVS code.

I worked out a pretty good algorithm for selecting major and minor tic
locations for axes transformed by any continuous and either strictly
increasing or strictly decreasing function, such that:
 - tic labels are "simple"
 - tic labels do not overlap
 - the distances between tics are roughly equal
 - the numeric value corresponding to any minitic is unambiguous
 - the distances between minitics are roughly equal, and small enough
   that the numeric value of any point can be estimated by eye.

You can find standalone demo code and a couple of example plots at
http://jrv.oddones.org.

I need help integrating this into gnuplot - e.g. 
 - choosing command syntax for declaring a transformed axis
 - command parsing
 - evaluating the transformation function for chosen points
 - displaying both major and minor tics at arbitrary locations
(I found the user could choose locations for major tics but not minor
tics)
 - maintaining the current log axis algorithm in parallel, and
allowing the user to choose either for now.  

It's been two years since I worked on this.

	  - Jim Van Zandt