1. A computer-implemented method comprising: obtaining a procedural model, the procedural model specified as a hierarchy of two or more modules, each module specifying a sequence of one or more procedural methods, and at least one module specifying a geometry to be drawn by the procedural model according to the procedural methods; and executing the procedural model to draw a graphical structure comprising one or more geometries specified by the two or more modules, said executing the procedural model comprising: executing each of the two or more modules according to the hierarchy, said executing each of the two or more modules comprises comprising: sequentially executing the one or more procedural methods of the respective module, execution of at least one of the procedural methods being controlled by one or more parameters of the respective procedural method, each parameter controlling a specific behavior of a respective procedural method.