A method for imaging, comprising: receiving a three-dimensional, 3D, image mesh of a tubular structure within a body of a subject, wherein said tubular structure is one of: an inferior vena cava, a superior vena cava, a coronary sinus, a coronary artery, an aorta, a pulmonary vein, a blood vessel and an esophagus; converting the 3D image mesh to a half-edge data structure; and then identifying a plurality of points of the half-edge data structure appearing in the 3D image mesh on a surface of the tubular structure; defining rings, each ring passing through a respective subset of the points of the half-edge data structure on the surface and encircling the tubular structure, wherein defining the rings comprises specifying a starting point, and incorporating in the respective subset for each ring a group of the points that are equidistant from the starting point; and making topological connections between the rings using relations between the half-edges, thus separating the rings that belong to different branches; arranging the branches in a tree structure; identifying the root of the tree structure; defining a new set of rings, each new ring passing through a respective subset of the points of the half-edge data structure on the surface of the tubular structure, wherein defining the new set of rings comprises using the root of the tree structure as the new starting point, and incorporating in the respective subset for each new ring a group of the points that are equidistant from the new starting point; making topological connections between the new rings using relations between the points of the half-edge data structure, thus separating the new rings that belong to different new branches; arranging the new branches in a tree structure; connecting the centers of the new rings to make a first approximation of the center line of the branches at a branch construction step; adjusting the new rings so that they are orthogonal to these center lines at a ring normalization step; and combining the rings to create a 3D geometrical model of the surface of the tubular structure. receiving a three-dimensional, 3D, image mesh of a tubular structure within a body of a subject, wherein said tubular structure is one of: an inferior vena cava, a superior vena cava, a coronary sinus, a coronary artery, an aorta, a pulmonary vein, a blood vessel and an esophagus; converting the 3D image mesh to a half-edge data structure; and then identifying a plurality of points of the half-edge data structure appearing in the 3D image mesh on a surface of the tubular structure; defining rings, each ring passing through a respective subset of the points of the half-edge data structure on the surface and encircling the tubular structure, wherein defining the rings comprises specifying a starting point, and incorporating in the respective subset for each ring a group of the points that are equidistant from the starting point; and making topological connections between the rings using relations between the half-edges, thus separating the rings that belong to different branches; arranging the branches in a tree structure; identifying the root of the tree structure; defining a new set of rings, each new ring passing through a respective subset of the points of the half-edge data structure on the surface of the tubular structure, wherein defining the new set of rings comprises using the root of the tree structure as the new starting point, and incorporating in the respective subset for each new ring a group of the points that are equidistant from the new starting point; making topological connections between the new rings using relations between the points of the half-edge data structure, thus separating the new rings that belong to different new branches; arranging the new branches in a tree structure; connecting the centers of the new rings to make a first approximation of the center line of the branches at a branch construction step; adjusting the new rings so that they are orthogonal to these center lines at a ring normalization step; and combining the rings to create a 3D geometrical model of the surface of the tubular structure.