Imitating GNUPlot's "Impulse" format?

[Irv Thomae]

For plotting data points (one per minute) which have a high degree of random variation, I'd like to use what GNUplot calls "impulse" presentation. Instead of connecting successive points to form a line graph, each point would have a purely vertical line reaching up to it from the x-axis.

In a mathematical sense at least, this sounds like a limiting case of a time-series bar graph, as the bar width approaches one pixel. Is that the most practical way to accomplish it, or could it be done more efficiently by extending StandardXYItemRenderer's current {LINES, SHAPES, IMAGES,DISCONTINUOUS} set of options?

Thanks,
Irv Thomae

[Dave Gilbert]

Hi Irv,

I would just create a new implementation of the XYItemRenderer, because I think the StandardXYItemRenderer is already overloaded. It's easy enough to switch from one renderer to another, so there's not really a need for one renderer to have lots of different options the way that StandardXYItemRenderer does now.

I'm about to check into CVS a new renderer (XYDotRenderer) that just draws dots at each x,y point, instead of trying to draw a shape or line or anything fancy. It would be pretty easy to copy and modify that class to draw a vertical line as you suggest.

Regards,

DG.

[Kishore]

Hi,
Is it possible to draw a Trend Line using This JFreeChart.
thanks,
Kishore.

[Irv Thomae]

Hi Dave,
Just today I found time to implement the suggestion yo made a week ago: namely, to extend XYDotRenderer.
I "wrote" a new class called "XYImpulseRenderer", which is an almost exact copy of XYDotRenderer, with just one change:
Within drawItem( lots of parameters), the XYDotRenderer class has

double transX = domainAxis.translateValueToJava2D(x, dataArea);
double transY = rangeAxis.translateValueToJava2D(y, dataArea);

g2.drawRect( (int)transX, (int)transY, 1,1);

Seeing that this draws the point as a 1 x 1 "rectangle", I simply substituted

g2.drawRect( (int)transX, (int)transY, 1,(int)transY);

to draw a "Rectangle" 1 unit wide but as high as the point's position.
And it works - mostly. However, some of the vertical lines thus created are broken up into 2 or more "pieces", with substantial amounts of white space between their successive parts. Visually, these breaks don't show much of a pattern - they look quite random, _not_ (for example) as if a constant-width band of white had been drawn across them. Taller lines are affected much more than shorter ones, but that's the only generalization I can make.

Can you shed any light on this mystery?

Thanks,
Irv

[Tom Carden]

Irv,

I'm not sure, but I think your problem could be artifacts due to antialiasing. If you turn off antialiasing do they change/disappear?

Tom.

[Irv Thomae]

Tom,
Thanks for the suggestion. I just tried this:


// .... immediately after JFreeChart chart = ChartFactory.createXXX() :
chart.setAntiAlias(false);

Unfortunately, it seems to make no difference.

AFAIK, nobody has ever reported gaps in a vertical axis, although thta of course is drwn as a line. Apparently it's a bad idea to draw these vertical lines as "rectangles", though I can't see why that should be true....

[Dave Gilbert]

Hi Irv,

You could probably use a Line2D or g2.drawLine(...) and see if that makes the problem go away.

Regards,

DG

[Irv Thomae]

Hi David,
Yes, Line2D(..) does make the problem go away, as does g2.drawLine(..), and the latter seems to be about 10% faster.

To save anybody else the same frustration, I'll confess that the first time I tried to use either g2.drawLine or g2.draw(new Line2D.Double(...) , I wrote the arguments as (transX, transY, transX, 0) - and couldn't understand why the entire plot was filled in. Of course, I had overlooked the need to translate my 0 to Java2D coordinates.

XYDotRenderer is a nice clean substitute for XYItemRenderer, but it does lack the latter's ability to use a logarithmic vertical axis. Do you expect to extend it in that way any time soon?

Thanks,
Irv