Feature Cell Origin

When you create feature cells, it is important that you take into account the way that these cells are varied when the different parameter sets are applied. This directly affects the location of the cell origin, or placement point.

Take, for example, a feature cell that is based on a slab feature that has a blend and a cut feature added to it. In this cell, the origin (0,0,0) of the base cell is in the lower left corner of the slab. Any parameter sets that change the dimensions of the underlying slab will cause the new dimensions to be calculated relative to the centroid of the underlying slab.

Original cell, with origin at lower left corner of underlying slab.

Thus, if a parameter set reduces the length and width of the underlying slab, the cell origin will be outside the feature cell.

With the underlying slab reduced, the origin falls outside the cell.

Similarly, if a parameter set increases the length and width of the underlying slab, the cell origin will now be located inside the feature cell.

When the underlying slab is enlarged, the origin falls inside the cell.

To avoid this "shifting" of the cell origin you can use a different modeling method to create your feature cells. In the above example, rather than using a primitive for the underlying solid, you could use an extruded dimension driven (DD) profile. When you create the DD profile, you create a fixed point set at the required location for the cell origin. All changes in dimensions then would be relative to this fixed point, which is also the cell origin.

In the previous example, the underlying slab can be created from a rectangular DD profile, which is extruded and then the blend and cut features added. In this case, the fixed point for the profile would be the lower left corner as before. No matter which parameter set is chosen, the origin of the cell remains in the lower left corner of the cell.

In each case, the origin of the feature cell is the lower left corner of the cell.

Typically, the workflow for creating a feature cell of this type is:

Create a dimension driven (DDD) profile with variables for the required dimensions.
Create a feature solid using the profile.
Create a Global Variables/Equations list, which will be used by the feature cell.
Use the Modify Profile tool to assign the global variables to the (dimension driven) profile.
Create the parameter sets.