In the centre tapped rectifier:
It seems as if the highlighted ground line would provide a short circuit for any current developed between the top/bottom wires and the centre tap, eliminating any output voltage.
Additionally, in the bridge rectifier:
The current is supposed to flow through D1/D2 or D3/D4, but the presence of the ground makes it seem like the current would get through the resistor and then short to ground. This wouldn't affect the output voltage but it still seems strange to me.
I'm guessing I'm not grasping how grounding actually works, so a simple explanation for these circuits would be appreciated. Thanks.