Problema con jpgraph y postgresql

[Montes28]

hola amigos espero me puedan ayudar, estoy empezando a trabajar con jpgraph y necesito plotear una consulta a una base datos.

tome como referencia el ejemplo que se encuentra en la documentacion.

en el dataset01.inc.php
los datos estan de la siguiente manera

$ydata = array(
0 => 1.0885908919277, 1 =>
0.99034385297982, 2 => 0.97005467188578, 3 =>..............

$xdata = array(

0 => 444348000, 1 => 446853600, 2 =>
449532000, 3 => 452124000, 4 =>..................................

Código PHP:

include('inc/jpgraph.php');
include('inc/jpgraph_line.php');
include('inc/jpgraph_date.php');
include('inc/jpgraph_utils.inc.php');
 
// Get a dataset stored in $xdata and $ydata
include('inc/dataset01.inc.php');
 
 
$dateUtils = new DateScaleUtils();
 
// Setup a basic graph
$width=700; $height=400;
$graph = new Graph($width, $height);
$graph->SetScale('datlin');
$graph->SetMargin(60,20,40,60);
 
// Setup the titles
$graph->title->SetFont(FF_ARIAL,FS_BOLD,12);
$graph->title->Set('Development since 1984');
$graph->subtitle->SetFont(FF_ARIAL,FS_ITALIC,10);
$graph->subtitle->Set('(Example using the builtin date scale)');
 
// Setup the labels to be correctly format on the X-axis
$graph->xaxis->SetFont(FF_ARIAL,FS_NORMAL,8);
$graph->xaxis->SetLabelAngle(30);
 
$lp1 = new LinePlot($ydata,$xdata);
$lp1->SetWeight(0);
$lp1->SetFillColor('[email protected]');
$graph->Add($lp1);
 
// And then add line. We use two plots in order to get a
// more distinct border on the graph
$lp2 = new LinePlot($ydata,$xdata);
$lp2->SetColor('orange');
$graph->Add($lp2);
 
// And send back to the client
$graph->Stroke();
 

los datos devuelos por la consulta son los siguientes

campo 1 campo 2
timestamp with time zone real
"2012-06-27 00:00:46-05" 2
"2012-06-27 00:07:34-05" 5
"2012-06-27 00:13:03-05" 20
"2012-06-27 00:15:19-05" 15
"2012-06-27 00:22:19-05" 10


y mi codigo es el siguiente

Código PHP:

include('inc/jpgraph.php');
include('inc/jpgraph_line.php');
include('inc/jpgraph_date.php');
include('inc/jpgraph_utils.inc.php');
 
$dateUtils = new DateScaleUtils();
 
 
$width=700; $height=400;
$graph = new Graph($width, $height);
$graph->SetScale('datlin');
$graph->SetMargin(60,20,40,60);
 
$graph->title->SetFont(FF_ARIAL,FS_BOLD,12);
$graph->title->Set('Development since 1984');
$graph->subtitle->SetFont(FF_ARIAL,FS_ITALIC,10);
$graph->subtitle->Set('(Example using the builtin date scale)');
 
 
$graph->xaxis->SetFont(FF_ARIAL,FS_NORMAL,8);
$graph->xaxis->SetLabelAngle(30);
 
                $servidor = 'localhost';
        $bd = 'tremor';
        $usuario = 'postgres';
        $contrasenia = '*****';
        $tabla = 'tremor';
        
 
        global $servidor, $bd, $usuario, $contrasenia;
        $db = new PDO('pgsql:host=' . $servidor . ';dbname=' . $bd, $usuario, $contrasenia);
 
        $consulta = $db->prepare("SELECT campo5, campo1 FROM tremor");
        $consulta->execute();
 
        while($fila = $consulta->fetch(PDO::FETCH_ASSOC))
        {
        $xdata[] = $fila['campo5'];
        $ydata[] = $fila['campo1'];
 
        }
 
 
$lp1 = new LinePlot($ydata,$xdata);
$lp1->SetWeight(0);
$lp1->SetFillColor('[email protected]');
$graph->Add($lp1);
 
 
$lp2 = new LinePlot($ydata,$xdata);
$lp2->SetColor('orange');
$graph->Add($lp2);
 
 
$graph->Stroke();
 

el error que obtengo es el siguiente:
cannot use auto scaling since it is impossible to determine a valid min/max value of the y-axis (only null values)