The Coordinate System can be reviewed or modified using the Coordinate System form.
All locations in the model are ultimately defined with respect to a single global coordinate system. This is a three-dimensional, right-handed, rectangular (Cartesian) coordinate system. The three axes X, Y, and Z are mutually perpendicular, and satisfy the right-hand rule.
By default, the top of all slabs and beams lie on the XY (horizontal) model datum plane. Columns, braces, walls and ramps extend below or above this horizontal plane in the Z direction. Point loads/displacements and restraints/springs may be oriented along any of the three principal axes, while line and area loads and springs are typically defined in the gravity or vertical direction. Vertical deflections are associated with the Z-axis.
To draw objects easily, the graphical user interface allows multiple grid systems of both Cartesian and cylindrical grid lines to be defined. Those grid lines are basic construction lines and are intended to make it easy to draw objects. Do not confuse the grid system grid lines with the finite element mesh, which is generated by the program and used in the analysis.
Snap options are available that will cause the cursor to snap to grid lines and grid line intersections (see the Draw menu > Snap Options command).
Coordinate System Definition Form