Creating referenced objects

Hi 

I have purchased Draftsight to do simple site plans for creating manufacturing drawings. For example I have a floor plan of the Hospital loading dock that is 4metres long and 3.5 metres deep. So I draw a square of that size. no problems.

There is a support column of 600mm Diameter that is 1.5 Metres out from the end of the loading bay and the centre of this column is 1 metre back from the side wall of the loading dock. How do I find the centre point of this column in relation to the loading dock I have drawn as a square.

this is a very simple one, some of this sites have trees, posts, grids, grates etc and I need to have them in pretty much the right spot so as not to block, damage of have access issues when the waste truck comes to pick up the waste unit.