Surface Grid Extrusions

Hello,

I just started using grasshopper and Im trying to create a grid on a surface where i would like to extrude only certain blocks of the grid at certain positions.

Anyone knows how i can find the positions of the subdivided surfaces since i used the script for the Surface trigrid from the Primer book but they exploded the surfaces to get the corner points and draw the triangles i just want to find the position of these subdivided surfaces.

Ive attached a picture of what im trying to achieve.