We consider closed curves in the three regular and eight semiregular grids in the plane, in which each vertex and each edge can be repeated a limited number of times. We define the conditions for such curves to be self-avoiding, and we present a linear-time algorithm to check them. We define the orientation of such curves. We propose a classification of their vertices, and we give a unifying formula relating the number of different types of vertices, valid in the regular and semiregular grids. Our results can be used in the plane tiling applications.

We address the problem of computing discrete geometric moments on 2D binary images encoded in the quadtree data structure. We do this by precomputing central moments of the squares of side length 2k, and using the connection between ordinary and central moments. Compared with the state of the art for images encoded as quadtrees, our method considerably improves the efficiency of moment computation.

We consider paths in the 2D square grid, composed of grid edges, given as a sequence of moves in the four cardinal compass directions, without U-turns, but possibly passing several times through the same vertex or the same edge (if the path is open, it cannot pass twice through its starting vertex). We propose an algorithm which reports a self-crossing if there is one, or otherwise draws the path without self-crossings. The algorithm follows the intuitive idea naturally applied by humans to draw a curve: at each vertex that has already been visited, it tries to insert two new segments in such a way that they do not cross the existing ones. If this is not possible, a self-crossing is reported. This procedure is supported by a data structure combining a doubly-linked circular list and a skip list. The time and space complexity is linear in the length of the path.

We propose a characterization of discrete analytical spheres, planes and lines in the body-centered cubic (BCC) grid, both in the Cartesian and in the recently proposed alternative compact coordinate system, in which each integer triplet addresses some voxel in the grid. We define spheres and planes through double Diophantine inequalities and investigate their relevant topological features, such as functionality or the interrelation between the thickness of the objects and their connectivity and separation properties. We define lines as the intersection of planes. The number of the planes (up to six) is equal to the number of the pairs of faces of a BCC voxel that are parallel to the line.

A new combinatorial 3-coordinate system for cells in the face centered cubic grid is presented, and some of its properties are detailed. Three independent coordinates are used to address the voxels (rhombic dodecahedra), their faces (rhombs), their edges and the points at their corners. The incidence (boundary and co-boundary) and adjacency relations between the cells can easily be captured by these coordinate values. The new coordinate system can effectively by applied in various image processing morphological and topological operations.

We describe a dual graph-based representation for the ascending and descending Morse complexes of a scalar field, and a compact and dimension-independent data structure based on it, which assumes a discrete representation of the field as a simplicial mesh. We present atomic dimension-independent simplification operators on the graph-based representation. Based on such operators, we have developed a simplification algorithm, which allows generalization of the ascending and descending Morse complexes at different levels of resolution. We show here the results of our implementation, discussing the computation times and the size of the resulting simplified graphs, also in comparison with the size of the original full-resolution graph.