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Fuzzy Tolerance |
What is Fuzzy tolerance? Fuzzy tolerance is an extremely small distance insignificant for the precision of your dataset. It represents the minimum distance between vertices. If vertices are found closer to each other than the Fuzzy Tolerance they are snapped together.
Why do we need to use it? There is a limitation in the precision with which we can represent the numbers, so in many cases the numbers need to be rounded in order to be used in the calculations. Imagine that we want to split two intersecting polylines and create a node in the intersection. We find the intersection point (the coordinates are rounded), then we split each polyline with the intersection point found. The coordinates of the split point for each polyline are rounded again. As a result the two split points might not coincide exactly. The fuzzy tolerance is used to snap these two points together in order to ensure correct topological relationships between the two (after the splitting - four) polylines.
What Fuzzy tolerance should I use? The default Fuzzy tolerance in ET GeoTools is calculated from the extents of the layer using the formulae (W + H) / 2000000 where W and H are the with and height of the extent envelope. The larger values of the Fuzzy tolerance used the more the original shapes are approximated in order to snap to each other. If the fuzzy tolerance is too small, some of the problems of the data might not be fixed. The best option is to use Fuzzy tolerance close to the default and then clean the remaining problems with the tools available.| Copyright © Ianko Tchoukanski |