A sightline, sight line or visual axis, is a normally unobstructed line-of-sight between an intended observer (or spectator) and a stage, arena, or monument, for example. Sightlines are a particularly important consideration in theatre and stadium design, road junction layout and urban planning. In cities such as London, construction within sightlines is restricted to protect the key views of famous landmarks.[1]

http://en.wikipedia.org/wiki/Sightline

The Origins of the Sightline Calculation

Seating tiers in modern stadia, arena and theatres are defined the following formula:
C = D ((N+R)/D+T) - R
The origin of this formula appears to dates back to a concept of iseidomal or is acoustic curves in lecture halls (equal seeing or equal hearing curves) first presented byJohn Scott Russell on the 16th of May 1838 in a presentation to the Society of Arts for Scotland.
The first building this theory was used to design seems to be the Auditorium Building in Chicago by Adler and Sullivan 1889.
As part of Populous’ ongoing Research and Development program we are currently developing 3rd Generation sightline evaluation with some of the world leading experts in the field.

http://populous.com/posts/the-origins-of-the-sightline-calcu...

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Note added at 30 mins (2013-11-04 23:09:43 GMT)
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ISOPTICA
Para el diseño del auditorio se requiere hacer el estudio y trazo de la isoptica, para tener una mejor visión como espectador

http://lorenajijon.blogspot.com.es/2010/11/elementos-constru...

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Note added at 39 mins (2013-11-04 23:19:19 GMT)
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INTRODUCCIÓN:
La isóptica es uno de los elementos importantes en cualquier espectáculo, (cines, teatros, templos, estadios, salas de reunión, etc.) tanto ó mas importante que el sonido, la proyección, la acústica, y aun mismo las butacas, etc. Pues puede haber deficiencia en cualquiera de ellos, pero si no existe buena visibilidad, el espectáculo puede ser nulo si no existe la visual.

http://www.industriasideal.com/isoptica/