Learning OpenCV

Sequences

One kind of object that can be stored inside a memory storage is a sequence. Sequences are themselves linked lists of other structures. OpenCV can make sequences out of many different kinds of objects. In this sense you can think of the sequence as something similar to the generic container classes (or container class templates) that exist in various other programming languages. The sequence construct in OpenCV is actually a deque, so it is very fast for random access and for additions and deletions from either end but a little slow for adding and deleting objects in the middle.

The sequence structure itself (see Example 8-1) has some important elements that you should be aware of. The first, and one you will use often, is total. This is the total number of points or objects in the sequence. The next four important elements are pointers to other sequences: h_prev, h_next, v_prev, and v_next. These four pointers are part of what are called CV_TREE_NODE_FIELDS; they are used not to indicate elements inside of the sequence but rather to connect different sequences to one another. Other objects in the OpenCV universe also contain these tree node fields. Any such objects can be assembled, by means of these pointers, into more complicated superstructures such as lists, trees, or other graphs. The variables h_prev and h_next can be used alone to create a simple linked list. The other two, v_prev and v_next, can be used to create more complex topologies that relate nodes to one ...