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PR Quadtree

PR Quadtree. Geographical Data Structure. Background. The structure of a BST is determined by the order of the data Depending on the order we can get either very balanced or very unbalanced trees. This is not a good way to build a tree

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PR Quadtree

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  1. PR Quadtree Geographical Data Structure

  2. Background • The structure of a BST is determined by the order of the data • Depending on the order we can get either very balanced or very unbalanced trees. • This is not a good way to build a tree • A PR Quadtree is a way to handle particular data that can be mapped to a “world”

  3. Quadtrees • Quadtrees are a whole family of trees. • They are all based on the use of recursive decomposition • They can be differentiated by two ways: • The type of data they represent • The principle guiding the decomposition process • The resolution (variable or not)

  4. PR Quadtree • Data is stored in leaves only. • Internal nodes have four pointers. • Pointers are labeled as NW, NE, SE, SW • If during insertion a leaf node is found and the coordinates of the leaf node’s data differ from the data that is trying to be insert, then a new internal node is created and both pieces of data are inserted

  5. Node Considerations • This is a natural case where internal nodes and leaf nodes are different. • A natural choice here would be to use inheritance. • However most of the functions would be very different; so polymorphism might not really be all that helpful • If you use inheritance about the only common method might be isLeaf() • You will then have to cast the node as either an internal or leaf node

  6. Insertion • As you build a PR Quadtree, you will need to create both internal and leaf nodes • The process is recursive • You could put an insert method in the node class. • What would happen here is a little different from how you may have done insertion in the past

  7. Node’s handling Insertion • You could polymorphically call insertion on a node and it would “know” which insertion to call • The internal node would ask the data its coordinates and determine where it goes. • In order to do this, the method needs to know some additional information • It needs to know the corner of the world and the width of the world.

  8. Leaf Insertion • The leaf node insertion would have to do some more work • First it would need to check to make sure that the data that is trying to be inserted isn’t already in the tree • If not, then it needs to create a new internal node • Then ask the new node to insert both the data that is already in the tree and the data that is trying to be inserted

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