Legend Question

[Andy Lawton]

I have a graph with two plots and two separate Y axis. If I add a legend to
this plot, the colours for the legend are OK, but the second plot comes out
red, when I am expecting blue.

$leg=array("Gauge Error","Speed");

$plot = new PHPlot; 
$plot = new PHPlot(800, 350);
$plot->SetDataColors(array('red',"blue"));
$plot->SetLegend($leg);
$plot->SetImageBorderType('plain');
$plot->SetPrintImage(False);
$plot->SetPlotType('lines');
$plot->SetDataValues($gerror);
$plot->SetPlotAreaWorld(NULL, -10, NULL, 10);
$plot->SetPlotType('lines');

# Set margins to leave room for plot 2 Y title on the right.
$plot->SetMarginsPixels(50, 50);
//Turn off X axis ticks and labels because they get in the way:
$plot->SetXTickLabelPos('none');

$plot->SetXTickPos('none');

$plot->DrawGraph();

//plot 2

$plot->SetDrawPlotAreaBackground(False); // Cancel background
$plot->SetPlotType('lines');
$plot->SetDrawYGrid(False); // Cancel grid, already drawn
$plot->SetDataValues($spd);
$plot->SetPlotType('lines');
$plot->SetPlotAreaWorld(NULL, 0, NULL, NULL);
$plot->SetYTickPos('plotright');
$plot->SetYTickLabelPos('plotright');
//$plot->SetLegendPosition(0, 0, 'image', 0, 0, 5, 5);
$plot->DrawGraph();

# Now output the graph with both plots:
$plot->PrintImage();

If I then add $plot->SetDataColors('blue'); on the second plot, it does get
plotted with a blue line and the first with a red line, but the legend colours
are blue for both plots.

What am I doing wrong?

[lbayuk]

You haven't shown what your data arrays look like, or exactly what you are
trying to do, so this might not be the right answer. I assume you want the
first plot (with a single data set) to be red, and the second plot (also with
a single data set) to be blue, and a legend to show a red and a blue entry.

Here's how you do it. For the first plot, exactly what you have now:

$plot->SetDataColors(array('red',"blue"));
$plot->SetLegend($leg);

Note that 'blue' is only there for the legend. Your data array has a single
data set and it will plot in red.

For the second plot, include this:

$plot->SetDataColors(array("blue"));
$plot->SetLegend(NULL);

Now your second plot will be in blue, and there will be no legend for this
plot. (If you don't cancel the legend, you get a second one, but since you
don't move it, it overlays the first.)

Does that help?

(FYI, you are creating 2 PHPlot objects - the 2nd replacing the first?)

[Andy Lawton]

Thanks for the reply. Your solution works perfectly for me.

I am plotting two graphs on the same plot, but with different scales. That's
why there's one Y axis on the left and one on the right. I just followed the
example in the documentation. The data looks like this:

$gerror[]=array("",$line[$ifound[1]]);
$spd[]=array("",$line[$ifound[0]]);