checking sum of the contact forces was hiding negative forces. Use norm instead (#10)

Author: rubengrandia

xpp_vis/src/rviz_robot_builder.cc

@@ -151,7 +151,7 @@ RvizRobotBuilder::CreateEEForces (const EEForces& ee_forces,
 
  Marker m = CreateForceArrow(f, p);
  m.color = color.red;
- m.color.a = f.sum() > 0.1? 1.0 : 0.0;
+ m.color.a = f.norm() > 0.1 ? 1.0 : 0.0;
  m.ns = "ee_force";
  vec.push_back(m);
  }