Current source with grounded Load and floating power supply
A caveat to this circuit is the current does not flow to ground, which is hard to wrap your head around. Because the circuit is floating and power is not sourced from ground (like it normally is) the current returns back to the source through R3. All of the current through the load goes back through R to return to the source. The vgnd or com node is negative relative to the ground. 

The ground in this circuit merely is a point at which to analyze the circuit. If you wanted to you could also put this node at 1000V and analyze it, and the current would be the same through the load.  



It's much easier to wrap your head around the circuit if you put the 0V node here, as you can easily spot the voltage divider for the load, and the current sense resistor R (or R3 in the pic below):