ofMesh vertices: accessing not in serial order

I have several questions related to accessing mesh vertices. I have a Java program developed in the Processing environment which builds a mesh representing a height field or terrain map – z(x,y) – and have converted that much to openFrameworks. Fine. The next step in the program is a convolution operation: basically running a 3x3 mask over the field to derive an array of gradient values. This was conveniently done in Processing viewing z-values as a 2D array because I need to access elements above, below as well as left and right of the cell in q

“Submit” inadvertently hit. Please ignore and see subsequent posting “…accessing the vertex vector”.