Databases and Systems

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data and we define two viewing schemes termed the “up-is-up” and “statue” modes.
For “up-is-up” the user defines an up-vector within the 3D reconstruction so that the
projection of that vector onto the selected plane will be parallel to the displayed yaxis.
By default this vector is defined to point up through the head so that a coronal
or sagittal view will be displayed with the head neural tissue at the top of the image.
For this mode the third Eulerian angle zeta is calculated by finding the component of
the up vector u that is perpendicular to the viewing direction v, i.e.
and R is the rotation matrix for = 0). This vector is in the original
coordinate frame and the required angle is determined by transforming w to the
viewing coordinates and calculating the angle with respect to the y’ axis:
The “statue” mode can be understood by considering the voxel image to be a statue
with the user walking around on a horizontal plane i.e. the x-y plane of the image.
The section seen by the user is rotated about its axis of intersection with the
horizontal for display on the screen. For the user the effect is that rotating a section
view around a vertical axis will result in a gradual rotation of the displayed image.
The Euler angles for this viewing mode are = –
Navigation
Locating a specific section within a 3D volume can be quite difficult so, in addition
to the option of panning though to a recognizable position which can then be defined
as the fixed point, a number other navigational aids are provided. The first is the
option of interactively defining a second fixed point which then reduces the number
of degrees of freedom to one, namely rotation around the line joining the two points.
This is termed the torsion, denoted and uniquely defines the viewing direction
n = cos( ) n2 + sin( ) n3,
where the orthonormal vectors n 1 and n 2 are defined by rotating the coordinate frame
so that the z-axis is parallel to the vector joining the two fixed points, namely the
vector