Representing an object in terms of sub-volumes

A method comprising:

• receiving, at a processor, data representing a three dimensional object;
• determining, using the processor, a modified data representation of the three dimensional object wherein, in the modified data representation, the three dimensional object is represented in terms of homogenous sub-volumes wherein:
• each homogenous sub-volume is homogenous with respect to a predetermined attribute;
• and
• each homogenous sub-volume contains locations which are within a common object boundary distance band of plurality of object boundary distance bands, wherein at least two object boundary distance bands partially overlap;
• and
• the homogenous sub-volumes are defined by merging locations into each homogenous sub-volume when a predetermined number of neighbouring locations are homogenous with respect to the predetermined attribute and are within a common object boundary distance band of the plurality of object boundary distance bands.