Hi Emmanuel, thank you for this new version! I have added it to the Plugin manager too.

A small bug (at least on Windows): when using the Alt and Shift keys to toggle the options, the checkbox is toggled on musedown, but it is toggled again on mouseup. Holding the key does not work (the checkbox blinks crazly).

Few suggestion for future improvements:

• Add incremental mode, i.e. add a value (instead of override) to the current elevation while moving the mouse over the grid. (It should be allowed to set negative values too to dig the terrain).
• Add smooth tool, would be helpful in conjunction with the new closed space function.