QZone

A QZone item is a 2D region represented by a hierarchical grid of squares that fit together to cover a region. This is a very compact and fast way to store and analyse complex regions. Each square can be divided into four quadrants and each quadrant sub-divided into quadrants repeatedly until they are uniform or the basic resolution of the data is reached. For example:

Note: The Q in the term QZone stands for "Quadtree".

Because the squares that make up the QZone are regularly sized, it is an extremely efficient way for the computer to model a 2D region. Detecting whether a point is inside a large QZone is hundreds of times faster than detecting whether the point is inside an equivalent Polygon item.

A drawback of using QZone items is that their edges are jagged, especially when you zoom in to them. When you create a QZone you can specify the size of the smallest square. By picking a small value you can stop the QZone appearing too jagged.

Note: When defining a cell size for the QZone you are creating, you need to make a compromise between the accuracy you require from the polygon and the speed of the query. Try and match the cell size to the capture scale of the data to obtain as accurate a match as possible.

Also see: Creating Polygon Items - Making large Polygons more efficient: QZones

Properties

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Properties


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