The `Fit surface' item on the `Segmentation' menu allows you to interpolate a smooth, continuous surface through the segmentation contours and visualise a surface rendering of it. When the `Surface' window pops up, you can set the resolution of the reconstruction using the `Resolution' slider. Expect high resolution interpolation to take some time, though the rest of Stradx will continue working during the calculation, albeit a little slowly. Note that the `Resolution' slider is quantised to a multiple of the B-scan pixel size.
When you have set the resolution, click the `Start' button. The progress of the interpolation is displayed at the bottom of the window. When the interpolation is completed, the interpolated surface is displayed in the drawing area in the middle of the window. You can move the viewpoint using the mouse and sliders in exactly the same manner as in the `Outline' window. By default, the surface is displayed as an opaque, triangulated mesh. Here's a surface interpolated through a segmentation of the hepatic veins.
If your segmentation includes multiple objects, these will be displayed simultaneously in the colours specified in the object selection panel. If you'd like to hide one or more of the objects, simply set the corresponding alpha value to zero.
No attempt is made to guess how the surface continues beyond the contours at the ends of the sweep: by default, these are left open, so you can look through them at the innards of the surface. If you would rather cap the holes with planar patches, select the appropriate object in the object selection panel and click the `Closed' toggle button.
By clicking on the `Vertices' toggle button, you can view the surface as a semi-transparent cloud of points (only the vertices of the triangulation are displayed, shaded according to the local surface normal). At high resolution, this is sometimes a useful way to view the surface, particularly when the surface is animated by changing the viewpoint.
The `Surface' window also displays the volume of the interpolated surface. Our studies have shown this volume estimate to be slightly less accurate than the estimate calculated using planimetry in the `Outline' window. Our advice is to trust the planimetry estimate, but only if the surface displayed in the `Surface' window looks plausible and the two volume estimates are similar.
The `Save PPM' button enables a snapshot of the surface to be saved to a ppm file. Alternatively, you can save the triangular mesh in a standard Geomview format by clicking the `Save GMV' button. The gmv file can then be loaded into Geomview for further visualisation and analysis. The mesh vertices are written to the gmv file in centimeters.
The displayed surface can also be used to mask the renderings in the `Reslice' and `Manifold' windows. This is especially useful for volume renderings. Click here for further details.
By clicking the `Landmarks' button, you can toggle on and off the display of any point landmarks which might be defined. When the `Landmarks' button is selected, point landmarks can also be placed relative to the displayed surfaces. You simply type the number of the landmark, which is then positioned below the mouse pointer. If the surface is fully opaque, the landmark is placed on the front surface; if it is semi-transparent, the landmark is placed midway between the front and back surfaces. You can change the opacity of the surface using the `Object Selection' panel. If you hold down the 'Control' key while placing the landmark, it will be positioned at the centroid of the first object under the mouse pointer. See the documentation for the `Measurements' window for further information about landmarks.
Click here to view a QuickTime movie (7 MBytes) showing Stradx being used to estimate the volume of a human bladder, using both the `Outline' and `Surface' windows.
When you have finished with the `Surface' window, or wish to interpolate a new surface, click on the `Done' button.