Y-Tick Increment calculation

[Badda]

Hi there,

First of all, THANK YOU for this absolutely great library for generating
reports. It makes my life so much easier :-))

However, Im facing one problem right now:

I believe the standard functionality of calcuating Y-Tick intervals (fixed to
1/10th of the Y data range) is not optimal. Thats why I would like to
implement a new functionality that takes into account:

• Y-ticks should always be anchored on Y=0
• Y-tick increments should be something that adds up to 10,100, etc (like 2, 2.5, 5, 10, 20, 25, 50, 100, ...)
• There should not be more Y-ticks (and Tick Lables if applicable) than can fit on the Y-Axis with a reasonable bottom- and/or top-margin. Eg: If I have a Y-Axis length of 100px, a Y-tick-label height of 8px and a tick bottom margin of 4px, no more than 8 ticks should be printed because 8*(8px+4px)=96px, which is just smaller than 100px.

To be able to accomplish this, I need the following information BEFORE drawing
the plot:

• Y-Axis total lenght (in px)
• Y-Axis total length (in World Coordinates)
• Y-Tick-Label height using the currently selected font

with this information, I can calculate the desired Y-Tick Increment.

Now my question: Is there a way, PHPlot can give me the desitred information?

Answers are highly appreciated :-))

Regards, Sebastian

[lbayuk]

Improvements to the automatic tick interval and range calculations have been
in the works for a long time now. Here are the 2 bug reports on the tracker:
Improve tick interval calculations and Fix automatic Y range calcula
tions.

It turns out to be a much harder problem than it seems. Calculating tick
intervals as K * 10 ^ N, where K is 1, 2, or 5 and N is any integer, is easy
enough, but there are other complications, such as date/time ticks intervals.
I still plan to do this, but it keeps getting pushed aside for other changes.

As for the Y ticks anchored on Y=0, I agree this would have been a better
default. But the ability to anchor the ticks at an X or Y value was only added
in PHPlot-5.4.0, so making SetYTickAnchor(0) the default could have changed
the appearance of many existing plots. I try hard to minimize cases where that
happens.

There isn't currently any capability for limiting tick labels based on
available space. I didn't think this would be a problem (I expected the plot
would become cluttered and hard to read with too many labels well before
running out of space). But this is somthing I need to think about.

[Badda]

Ok, I accomplished what I wanted to do with this code before calling
DrawGraph:

$plot->SetYTickAnchor(0);
$plot->SetCallback("draw_setup", function () use (&$plot) {
    // Y-Tick setup variables
    $k=array(1, 2, 2.5, 5);
    $margin=10; // minimum distance between Y-Tick lables in px

    // Calculate Y-Tick Increment
    $mintickinc=($plot->fonts["y_label"]["height"]+$margin)/$plot->yscale;
    $n=ceil(log10($mintickinc)*count($k));
    $inc=$k[$n%count($k)]*pow(10,floor($n/count($k)));
    $plot->SetYTickIncrement($inc);
});

[lbayuk]

OK, but I have to give you the standard caution about using PHPlot class
internal variables in your script, in this case fonts and yscale. There is a
real risk that your script will break any time you upgrade PHPlot, because
class variables often change, without much regard for compatibility.

(P.S. now I have to go read up on anonymous functions - I haven't seen that
syntax used before, especially the 'use' clause which is very briefly
documented, it seems.)