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Previous: Changing Raster Values by Geographic Feature
In this exercise, you will learn how to simplify linear features by removing unnecessary coordinates using theGeneralizerTransformer in FME - this operation is commonly referred to asweeding.
reducing-unnecessary-coordinates.fmwt
Note: Since you areworking on a public facing database, tables can occasionally be overwritten and/or modified. If your translation produces unexpected results, see theResetting the PostGIS Training Databasearticle.或者,您可以下载提供的文件(s) and replace the PostGIS reader with a reader of the appropriate format.
In this scenario, you want to simplify a bike path network to show the general path rather than every single turn. We will use the Douglas (Generalize) algorithm to reduce the density of coordinates by removing vertices, thus simplifying the line.
The Generalizer transforms or measures geometry features based on a specified algorithm. There are 4 types of algorithms: Generalizing, Smoothing, Measuring, and Fitting. In this exercise, you will use a Generalizing algorithm because you want to reduce the density of coordinates by removing vertices.
Next, specify the Generalization Tolerance. The Generalization Tolerance is a parameter that is used by the generalizing algorithm that is measured in the same units as the feature coordinates. For more technical details, see theGeneralizer Documentation.
You will be using the default algorithm, Douglas (Generalize) because it will remove vertices which causes a deviation of less than the Generalization Tolerance, but the location of remaining vertices are not altered. This algorithm is good at reducing the number of points in a line; however, it is not very good at preserving the shape or the spatial relationship of the line relative to other entities.
Data used in this tutorial originates from open data made available by theCity of Vancouver, British Columbia. It contains information licensed under the Open Government License - Vancouver.
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