Eliminate gap on the x-axis for lineplot

[Christoph Marbach]

Hi everybody, I am relatively new with jpgraph but quite desperate with the following problem: 

I draw an altitude chart from data in a gpx file. I store the altitude-data in an array $elevations for the y-axis and distance-data in $abs_distances for the x-axis. The graph plots correctly, but I can not get rid of the gap between the last value in the array and the right margin of the graph. The gap is variable dependent on the data in $abs_distances. 

The graph looks as follows: 

This is my jpgraph code: 

//-------------------- start jpgraph section -----------------
//Include der JPGraph library
require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_line.php');

// create new JpGraph-Diagram
$width=800;
$height=450;
 
// Create the graph and set a scale.
$graph = new Graph($width,$height);
 
// Setup the graph
$graph->SetMargin(80,20,0,20);
$graph->title->Set($tourentitel);
$graph->title->SetFont( FF_VERDANA , FS_BOLD , 16);
$graph->subtitle->Set($tourendatum);
$graph->SetScale('linlin');

$graph->xaxis->title->Set('Distanz (km)');
$graph->xaxis->SetColor('blue');
$graph->xaxis->title->SetFont( FF_VERDANA , FS_BOLD , 10);

$graph->yaxis->title->Set('Höhe (m)');
$graph->yaxis->SetColor('blue');
$graph->yaxis->title->SetMargin(25);
$graph->yaxis->title->SetFont( FF_VERDANA , FS_BOLD , 10);

// Create the linear plot
$lineplot=new LinePlot($elevations,$abs_distances);
$lineplot->SetColor("blue");
$lineplot->SetWeight(0);
$lineplot->SetFillGradient('#739560:1.8','darkblue'); //color setting from turqoise to darkblue

// Add the plot to the graph
$graph->Add($lineplot);

// draw and save the jpgraph Diagram as jpg image
$graph->Stroke($altprofiledir.'/tbaltprofile_'.$tourendatum.'.jpg');
//-------------------- end jpgraph section -----------------

Any ideas to solve this? I have tried a lot of different approaches (setting manual ticks, define right margin etc.), but no success. Thanks for any hints. - Chris

[w1djm...@gmail.com]

Does your distance array contain values going out to 18 as shown on the graph?

[Jon Taylor]

The code looks ok. It looks to me like you have some rogue data values in your file with the distance out to 18km.

[Christoph Marbach]

There are no rogue data values in the array. I checked it's content with print_r. The array $abs_distances contains calculated distances between track points. It always start with 0 ands end with something between 5.00 and 150 km. 

I also changed $graph->SetScale('linlin'); to $graph->SetScale('linint');  -> no change

Setting the ticks manually to 0,2,4,6,8,10,12,14 does not help either. 

[Scott Evans]

Have you confirmed you have the same number of entries in both  your $elevations and $abs_distances tables?  I believe (though please correct me if I'm wrong) that the two arrays are used to create x/y coordinates of each graph point, so if you don't have the same number in each array, you'll possibly get incomplete graphs. 

Scott

[w1djm...@gmail.com]

Would you be able to post, as plain text files or inline, a sample of data for both the X and Y axis so we can test things to try and help you further?

[Christoph Marbach]

Thanks for the help and thoughts so far. Yes, I have the same number of entries in both arrays. I have attached a csv file with full data. No problem to play around with it -> not critical. 

These exact arrays produce the problem (x-axis gap) which is shown in my first entry. 

[w1djm...@gmail.com]

I don't think you are going to be able to remove it based on the documentation and some testing. You are using INTeger for the X axis which implies that your values are integers but they are, in fact, not integers. Your largest value is 16.364 which is why the last X value is 17. Where the X axis ends is where 16.364 would be (the scale is too large to actually see that).

I tried changing all of the X axis values to integers but the graph ends up choppy and has steps up and down each side because the values on the X axis have very small differences. If you use the optional values on SetScale to end the X axis at 16 the chart spills off of the right side of the graph (as expected). It does remove the extra space but I think it looks bad/broken like that (see first image below). For that I used $graph->SetScale('intint',0,0,0,16);

You could still use that and increase the right margin slight so the X axis wouldn't run off of the right side as shown in the 2nd image below. For that I used $graph->SetMargin(80,25,0,20);

Bottom line is that JPGraph is doing exactly what it should be doing given the values you are asking it to graph.

[Christoph Marbach]

Thnx for testing. I also tried linear scale setting for both the x- and y-axis. Same result. I am able to determine the max-value=end-value of $abs_distances with something like $maxval=max($abs_distances); Then use $maxval to calculate the end of the lineplot. I can also determine the last tick which in my example data would be 16 (and omitting 17). Even if ticks are manually set: the gap remains.