In an example, a method includes receiving object model data representing at least a portion of an object that is to be generated by an additive manufacturing apparatus by fusing build material within a fabrication chamber. At least one of a number of different geometrical compensation models to be applied to the object model data may be selected, where the geometrical compensation models are to determine geometrical compensations to compensate for object deformation in additive manufacturing. An object generation operation based on a modification of the object model data using the or each selected geometrical compensation mode may be simulated and predicted attributes of the object when generated based on the or each simulation may be displayed.