I found some SO questions that were useful, but I need a complete reference guide for this api and its url paramters.
Edited
intent = new Intent(Intent.ACTION_VIEW,
Uri.parse("http://maps.google.com/maps?" + "saddr="
+ journey.getSourceGPSX() + ","
+ journey.getSourceGPSY() + "&daddr="
+ journey.getDestinationGPSX() + ","
+ journey.getDestinationGPSY()));
intent.setClassName("com.google.android.apps.maps",
"com.google.android.maps.MapsActivity");