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Views
14.2.1 Perspective View
The following picture illustrates how a perspective view is created.
Figure 135: Perspective projection
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The straight projection rays pass through each point in the model and intersect the
projection plane to form the projection contents.
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To facilitate the transformation from the world coordinate onto the view plane, the viewing
coordinate system is based on the viewer.
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Its origin, represented by the View.Origin property, is the viewer position.
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The viewer’s world coordinates are retrieved usng the View3D.EyePosition property.
Therefore, in 3D views, View.Origin is always equal to View3D.EyePosition.
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As described, the viewing coordinate system is determined as follows:
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The X-axis is determined by View.RightDirection.
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The Y-axis is determined by View.UpDirection.
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The Z-axis is determined by View.ViewDirection.
The view direction is from the target point to the viewer in the 3D space, and from the
screen to the viewer in the screen space.
The perspective view crop box is part of a pyramid with the apex at the viewer position. It is the
geometry between the two parallel clip planes. The crop box bounds the portion of the model that
is clipped out and projected onto the view plane.
Revit 2008 API User Manual
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