AnchoredSnapper

Categories

Geometries

Spatial Analysis

Brings lines, segments, end points or vertex points of features together if they are within a certain distance of each other, where one set of features is non-moving.

The difference between the AnchoredSnapper and the Snapper is that anchor features are considered to be accurate and consequently do not move.

 

Usage Notes

  • Any feature that undergoes dimensional collapse as a result of being snapped will be output through the Collapsed port.
  • A short cleanup step is performed after snapping. This step will remove duplicate points, and may create aggregates to preserve overlapping, directed segments.

Configuration

Input Ports

Features that may have Candidate features snapped to them. Arcs are snapped as linear features, and ellipses are snapped as polygonal features.

Features that may be snapped to Anchor features. Arcs are snapped as linear features, and ellipses are snapped as polygonal features.

Output Ports

Candidates whose geometry is changed by the transformer.

Candidates that leave the transformer without being changed.

  • If a line or area feature snaps down to a single location, it will be output as a Point geometry, through the Collapsed port.
  • If an Aggregate, MultiArea, or MultiCurve geometry has any parts snap down to a single location, a Point geometry for each part will be bundled up into a MultiPoint geometry and output through the Collapsed port. The remaining parts which did not snap down to a single location (if any) will be output as a group through the Snapped port.

The anchors that were used during snapping. If a candidate was snapped to a point along the segment of an anchor, a new node is inserted into the anchor’s geometry.

Features whose geometry is unsnappable (for example, having a non-finite coordinate) will be rejected and output via this port.

Rejected features will receive an explanatory fme_rejection_code attribute.

Rejected Feature Handling: can be set to either terminate the translation or continue running when it encounters a rejected feature. This setting is available both as a default FME option and as a workspace parameter.

Parameters

Group By

If Group By attributes are selected, features are only snapped to other features with the same values in the group by attributes.
Complete Groups

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.

There are two typical reasons for using When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with When All Features Received may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

Snapping Type

When Snapping Type is End Point Snapping:

  • The transformer snaps endpoints of features that enter via the Candidate port to endpoints of features that enter via the Anchor port. Anchor features are not output.
  • Point features can be used as Anchor or Candidate features, and Candidate points will be snapped together (or to a linear base feature) as well.
  • The transformer will not alter area features.

When Snapping Type is Vertex Snapping:

  • The transformer snaps vertices of features that enter via the Candidate port to vertices of features that enter via the Anchor port. Anchor features are not output.
  • Point features can be used as Anchor or Candidate features, and Candidate points will be snapped together (or to a linear Anchor feature) as well.
  • The transformer will alter area features.

When this parameter is set to Segment Snapping:

  • The transformer snaps vertices of curves or points that enter via the Candidate port to lines of features that enter via the Anchor port, if their distances are within the specified Snapping Distance. Anchor features are not output.
  • The transformer snaps vertices of Candidate segments to Anchor segments if their distances are within the specified Snapping Distance at any point along the segment.
  • Candidate segments which cross Anchor segments will have new vertices introduced at the point of intersection, but the Candidate segments will not be split.
  • Area features are altered by this operation as its vertices and segments are snapped.

Snapping Distance

Snapping Distance specifies the distance, in ground units, that the snapping occurs between features.

Tolerance

When Snapping Type is Segment Snapping, this transformer performs data cleaning that is meant to improve the robustness of the results when they are used in other algorithms by ensuring that no two vertices in the snapped output are within tolerance of each other.

If Tolerance is set to Automatic, a tolerance will automatically be calculated for the cleaning operation, based on the size of the inputs. Otherwise, a custom tolerance may be used.

Add Additional Vertex

This parameter applies only when the end point of a feature is being snapped.

  • NEVER: the endpoint of a line is moved when it is snapped and no additional vertex is added.
  • ALWAYS: the original end point (start point) of the line becomes the second from the end (start) and a new vertex is added to complete the snap.
  • FORWARD_ONLY: a new vertex is added only when doing so creates an angle greater than 90 degrees with the original line segment. In this case, if adding the vertex would cause a less than 90-degree angle, the old end point is still moved.

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.

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.

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

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.

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 samples and information about this transformer on the FME Community.

 

Keywords: FixedSnapper BaseSnapper