In an example, object model data representing at least a portion of an object defining an initial object geometry is received, wherein the object is to be generated by an additive manufacturing apparatus by fusing build material using a radiant heater. Based on a non-uniform radiant heating distribution of the additive manufacturing apparatus, a modified object geometry may be determined, wherein a local modification of the object geometry is determined based on a local radiant heating parameter determined from the non-uniform radiant heating distribution.