These transformers work with linear referencing data structures on FME features. Some transformers allow you to create and apply measure-related information held in attributes onto the geometry of FME features.
Linear referencing uses measures to associate attributes or events to locations or portions of a linear feature.
FME previously supported writing of measures to Geodatabase, SDE, and Shape files via a special attribute containing a comma-separated list of measure values, corresponding to the coordinates of the feature. However, in order to further support writing of measures, we still had to come up with a set of measures to populate. Rather than pulling the measures from database tables and combining them into a CSV attribute before writing them out (like some applications do) there is a transformer called the MeasureGenerator, which populates an attribute with a comma-separated list of the distances from the start of the line to each point. This can then be sent to the “shape_measures” attribute and it will be written out.
The Snipper transformer performs the following functions:
Shortens the geometry of a line feature by snipping off a specified amount from the ends. The amount to snip from the beginning and end of the line can be specified as either a measurement in ground units or a percentage of the line's entire length, starting from the first coordinate.
Shortens the geometry of a line feature by snipping off vertices from the ends. The vertices from the original line which are to form the first and last vertices of the resulting line are specified as a numeric index, with "0" being the first vertex of the line.
This transformer can transform data that was stored in an “LRS” way into a segmented view (if you have a table of “whole” geometries, and another event table that says where on a particular line things begin and end, you can do a join, and then a snip of some kind, and get out the segments).
The LengthToPointCalculator calculates the length of a feature from its start until the closest spot to a point, and adds it as a new attribute. This can be used to create an LRS view from a segmented view, when combined in a clever way with the ArcFactory (LineJoiner) and ReferenceFactory (FeatureMerger).