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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.〔http://www.london.gov.uk/priorities/planning/vision/supplementary-planning-guidance/view-management London View Management Framework (LVMF) 2009.〕 Objects that have a direct line of sight with one another are said to be ''intervisible''. ==C-Value== Good sightlines allow spectators to see all areas of a venue stage or field of play. To ensure this designers utilize the C-Value. The vertical distance from a spectator's eyes to sightline of the spectator directly behind is called a ''C-value''. The C-value is a value that helps produce a rake. The stadium bowl rake if based on consistent C-Values will follow half of a parabola in section. The curvature will be greatest closest to the pitch and will become an increasingly flatter curve as it moves to the upper rows. As a general rule the rake or curve of the seating bowl will flatten as the first row of seats move away from the side-line for a constant C-Value. It is impractical to make different step heights for every single row. In practice the riser height is the same for a set of 4 or 5 rows at the bottom of the bowl with the number of rows in each same height set increasing for higher up rows. The uppermost tier could have only 2 or even 1 different step heights. *D = the horizontal distance from the eye to the point of focus *N = the riser height *R = the vertical height to the point of focus *T = the seating row depth It is the lowest rows of seats that are the most sensitive to the impact of the C-Value because of the very flat view angle to the touch line. The higher seats can have a reduced C-Value without impacting as seriously on the clear view of the field of play. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sightline」の詳細全文を読む スポンサード リンク
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