Distance transforms are a powerful tool for the accomplishment of different tasks in 2D/3D image processing and analysis, computer vision, visualization and graphics [PT92]. 2D fields registering a signed distance to object contours were used to interpolate surfaces of the segmented 3D objects in tomographic data [RU90,HZB92,JM94]. In [SB93] the technique was extended even for unsegmented gray-scale data. Brummer et at in [BMEL93] used the distance fields to estimate a probability of the brain tissue presence in the detection of brain contours in MRI data. The distance fields were further used to create bounding spheres for the collision detection in robotics [GS00], to build a skeletal representation of objects in colonoscopy and angioscopy [ZKT98,ZT99,BSB$^+$00,BKS01], to define a cost function in the registration of volumetric data sets [Bor88] and to flatten complex surfaces (a human colon) by means of a curvilinear ray casting [BWKG01].
Distances and distance fields play a key
role in volume graphics, namely in object representation, object-to-objects
metamorphosis techniques and in acceleration of volume data rendering.