The gnomon is a control used to adjust position and orientation of coordinate frames and to transform objects in the viewport.
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Moving the gnomon on the YZ plane:
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3D
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translation
Move the entire gnomon freely along the view plane in 3D by clicking the origin and moving the cursor.An example of moving
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Moving the gnomon origin:
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2D rotations
pt 1: move
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Rotation about an axis
Click the rotate axis control to rotate the gnomon about an axis.
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Rotation about the Y axis:
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Rotation about axis to align another axis
Click an arrow at the end of the rotate axis control to rotate the gnomon about an axis and align another axis.
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Example rotating about the Y axis and aligning the X axis:
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3D rotation to align axis
Click the sphere on an axis and then another point to align the axis in 3D.
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Rotating so that the Y axis aligns with a point:
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Cancel action when using the gnomon
Right-clicking when using the gnomon will cancel any moves.