Chapter 6

The Efficiency of Algorithms

6.1 How Is Algorithm Efficiency Measured?

We have seen that an important part of designing GIS algorithms is to make them run as quickly as possible. In the case of the simple point in a polygon test, for example, testing the point against the minimum bounding rectangle of the polygon could save a lot of unnecessary line intersection tests. A lot of things can affect how quickly an algorithm will run such as the speed of the computer and how many other tasks are running on it at the same time. However, many of these will be difficult to measure; so, in assessing how efficient an algorithm is, computer scientists concentrate on what is called algorithm complexity – how the performance of the algorithm is ...

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