MAPaint Technical Report:
3D Orientation Feedback

3D Orientation Feedback

The lines of intersection of each plane with respect to the others provides a form of feedback to the relative positions of each viewing plane however because the views are not projections from 3D onto the screen there are no perspective cues to help the user orient the different views. This is not very important for the normal orthogonal sections which presumably will be familiar to most users of the database but for non-standard viewing directions could make easy use of the atlas and recognition of structures more difficult.

As an additional aid to orientation a ``cartoon'' 3D perspective display of the enclosing rectangle plus the various viewing planes is shown in the main window of the paint program. These geometric objects are displayed using OpenGL which is now emerging as the standard 3D graphics API for all Unix/X11 systems and has been adopted as standard within Microsoft Windows systems. In the paint program we are currently using a public domain package ``Mesa'' which provides virtually all of the OpenGL functionality on a raw X11 server unless OpenGl extensions are available for the server. So that the 3D display is reasonably efficient only very simple graphical objects are used - rectangles to represent the viewing planes, boundary displays of the domains which can be toggled on or off. It is important that the 3D display does not dominate the cpu time otherwise the reasonably interactive browsing through the volume data and painting will be lost. Figure 3.5 shows the top-level window of the program MAPaint v1.00 with the boundary cartoon of the 9-day mouse embryo with a number of tissues (domains) displayed.

  

Figure: Top-level window of the computer program MAPaint v1.00 showing the 3D feedback available. The 9-day mouse embryo is shown as a series of outline contours, a number of anatomical domains are similarly depicted (red: neural tissue, blue: somites). Feedback for the position of two section views (not shown) are displayed, in one case as a solid plane, in the other just as the intersection polygon between the section plane and the voxel image 3D bounding box.ues to help the user orient the different views. This is not very important for the normal orthogonal sections which presumably will be familiar to most users of the database but for non-standard viewing directions could make easy use of the atlas and recognition of structures more difficult.