The Standard Linear Format (SLF) Reader module provides FME with the capability to read SLF files. This chapter assumes familiarity with the SLF format.
Overview
SLF data sets are ASCII format files that use the chain-node—also referred to as link-node or segment-node—data structure. This means that regardless of the number of features a segment might belong to, that segment is stored only once in the data set. By not storing repeated segments, the SLF format simplifies updates and corrections. It also avoids overlap and gap problems, as well as being responsive to thinning and generalization algorithms.
An SLF file logically consists of these four sequential records:
- the Data Set Identifier (DSI) record
- the Segment (SEG) record
- the Feature (FEA) record
- the Text (TXT) record
The DSI, SEG, and FEA records are required for each SLF data set, whereas the TXT record is optional. The contents of the TXT record are product-specific and the only type of TXT record recognized by the SLF reader is when SLF is used to implement Interim Terrain Data (ITD) in two-dimensional (2D) format.
FME accepts any valid SLF file as input, regardless of file name or extension.
This section outlines the features and attributes produced directly by the SLF reader. The slf_point, slf_linear, and slf_areal features produced by the SLF reader only contain references to the segments that make up the feature. By themselves, these features do not contain any coordinates. Through using a sequence of FME factories, specially designed to process the SLF features, FME can re-assemble the sequence of coordinates that make up each feature from the segments. This sequence of factories is described at the end of this chapter, under the heading Features Created by FME Factories.