1. A method of sight distance analysis comprising: acquiring a scene-graph representation comprising three dimensional entities; acquiring at least one three dimensional object representation within the environment of said scene graph; acquiring a target object representation; selecting at least one camera position; positioning said acquired target object representation in said scene graph representation at a distance from said selected at least one camera position; rendering said target object representation without rendering said at least one three dimensional object representation intervening between said observer and said target object representation; calculating a metric of said target object representation rendered without said intervening at least one three dimensional object representation; rendering said target object representation while rendering said at least one three dimensional object representation intervening between said observer and said target object representation; calculating a metric of said target object representation rendered with said intervening at least one three dimensional object representation; and determining a visibility factor as a function of the difference between said calculated metric of said target object representation rendered without said intervening at least one three dimensional object representation and said calculated metric of said target object representation rendered with said intervening at least one three dimensional object representation.