Angular nvd3 not showing - angularjs

Question

I am trying to display a real-time line-graph using angular.js nvd3 [1]. It should plot altitude vs. time.
The problem I am having is with getting the x-axis to show the time data array correctly. This is what it looks like:
http://i.imgur.com/PQeskpf.png
and this is the data that I am trying to show:
$scope.chart1data = [
{
"key": "Altitude",
"values": [{x:"2013-03-04_12:00:00",y:50},{x:'2013-03-04_13:00:00',y:1000}]
}
];
chart options:
$scope.chart1options = {
chart: {
type: 'lineChart',
height: 350,
x: function(d){ return d.x; },
y: function(d){ return d.y; },
useInteractiveGuideline: true,
dispatch: {
stateChange: function(e){ console.log("stateChange"); },
changeState: function(e){ console.log("changeState"); },
tooltipShow: function(e){ console.log("tooltipShow"); },
tooltipHide: function(e){ console.log("tooltipHide"); }
},
xAxis: {
axisLabel: 'Time',
tickformat: function(d) {
return d3.time.format('%Y-%m-%d_%H:%M:%S')(new Date(d))
}
},
yAxis: {
axisLabel: 'Altitude (m)',
tickFormat: function(d){
return d3.format('.02f')(d);
},
axisLabelDistance: 100
}
}
};
If anyone knows how to get the x axis to show month/date-hour:minute for each data point, and have it scaled by time I could really use some help!
[1] http://krispo.github.io/angular-nvd3/#/quickstart