Parametric design is a design method where features (such as building elements and engineering components) are shaped according to algorithmic processes, in contrast to being designed directly. In this method, parameters and rules determine the relationship between design intent and design response. The term parametric refers to input parameters fed into the algorithms. While today the term refers to the use of computer algorithms in design, there are precedents in the work of architects. Antoni Gaudí used a mechanical model for architectural design (see analogical model) by attaching weights onto a system of strings to determine shapes for building features, such as arches. Parametric modeling can be divided into two main types: Propagation-based systems, in which algorithms result in final shapes that are unknown based on initial parametric inputs. Constraint systems, in which final constraints are set and algorithms are used to define fundamentals (structures, material use, etc) that satisfy these constraints. So called "form-finding" processes are implemented through propagation-based systems. Form-finding optimizes certain design goals against a set of design constraints, meaning the final form of the designed object is "found" based on these constraints. History (early examples) Analogue parametric design One of the earliest examples of parametric design was the upside down model of churches by Antonio Gaudi. In his design for the Church of Colònia Güell he created a model of strings weighted down with birdshot to create complex vaulted ceilings and arches. By adjusting the position of the weights or the length of the strings he could alter the shape of each arch and also see how this change influenced the arches connected to it. He placed a mirror on the bottom of the model to see how it would look once built right-side-up. Features of Gaudí's method Gaudí's analogue method includes the main features of a computational of a parametric model (input parameters, equation, output): The string length, birdshot weight and anchor point location all form independent input parameters The vertex locations of the points on the strings being the outcomes of the model The outcomes are derived by explicit functions, in this case gravity or Newtons law of motion By modifying individual parameters of these models Gaudí could generate different versions of his model while being certain the resulting structure would stand in pure compression. Instead of having to manually calculate the results of parametric equations he could automatically derive the shape of the