TopferIndexCalculator

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)

where:

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.

Configuration

Parameters

Group Processing

Group By

One Topfer Index will be computed for each group. It will be output on each feature.

Complete Groups

Select the point in processing at which groups are processed:

When All Features Received	This is the default behavior. Processing will only occur in this transformer once all input is present.
When Group Changes (Advanced)	This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Editing Transformer Parameters

Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click beside the applicable parameter.

How to Set Parameter Values

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.

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters	Create your own editable parameters.

Dialog Options - Tables

Table Tools

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

Row Reordering

Enabled once you have clicked on a row item. Choices include:

Add a row
Remove a row
Move current row up one
Move current row down one
Move current row to top
Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

Cut a row - delete and copy to clipboard
Copy a row to the clipboard
Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

For more information, see Transformer Parameter Menu Options.

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Source Scale	The denominator for the scale of the source dataset. For example, if the scale is 1:250,000, the Source Scale should be 250000. See the Topfer Index equation in the description.
Destination Scale	The denominator for the scale of the destination dataset. For example, if the new potential scale is 1:500,000, the Destination Scale should be 500000. See the Topfer Index equation in the description.