Takes a set of point, linear, polygonal, and/or aggregate features, and calculates the Topfer Index based on user-provided source and destination scales.

The input features may be partitioned into groups based on attribute values using the Group By parameter, and one bounding box feature is output for each group. If the Group By parameter is not specified, then all input features will be processed together and a single bounding box will be output. If a given bounding box has zero area, it will become a line or a point.

To avoid the appearance of overcrowding or sparsity, maps drawn at different scales sometimes require a different level of detail. The Topfer Index is a measure used to predict how many features should be used at a new scale. The formula is given by:

n_dest = n_src * sqrt(M_src / M_dest)


n_dest is the number of features that should be shown at the destination scale, also referred to here as the “Topfer Index.” This is the value that this transformer will compute.

n_src is the number of features shown at the source scale (in this case, the number of features received per group).

M_dest is the denominator of the destination scale (taken from a parameter).

M_src is the denominator of the source scale (taken from a parameter).

Usage Notes

  • To retrieve the bounds of a feature into attributes, use the BoundsExtractor.



Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.

FME Community

The FME Community is the place for demos, how-tos, articles, FAQs, and more. Get answers to your questions, learn from other users, and suggest, vote, and comment on new features.

Search for all results about the TopferIndexCalculator on the FME Community.