Clipper

Divides Candidate features using Clipper features, so that Candidates and parts of Candidates that are inside or outside of the Clipper features are output separately. Attributes may be shared between objects (spatial join).

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Typical Uses

Identifying where points, lines, or areas fall inside, outside, and intersect with one or more reference areas (Clippers), and modifying their geometry and attributes accordingly.
Clipping features to perform calculations by Clipper area
Clipping rasters or point clouds to a regular or irregular area of interest
Clipping features to a map boundary for aesthetics

How does it work?

The Clipper takes in two sets of features:

Clippers: Areas or solids which will be overlaid on Candidate features to identify which of those features fall inside or outside the Clippers. Those features are split where they cross the boundaries of the Clippers.
The geometry of the Clippers is unchanged, and they are discarded after use and not output from the Clipper transformer.
Candidates: Features with any type of geometry, which are compared to the Clippers, and split into multiple sections along the Clipper boundaries if necessary. Each section is output as either falling Inside or Outside the Clipper. They may also receive attributes from the Clippers (spatial join).
Candidate geometry is only altered if it intersects with a Clipper. If it falls wholly inside or outside the Clipper, it is designated as such and output with its geometry untouched.

Output features receive a Clipped Indicator attribute (default name _clipped), which is set to “yes” for features that have been segmented, identifying features that were wholly inside or outside the clip boundaries and those that intersected the Clipper boundaries and so were modified.

The Clipper works on all geometry types. This diagram illustrates area-on-line and area-on-area vector clipping results.

(1) is a single area Clipper (in blue).
(2) are the Candidates, a red line that crosses the Clipper (1), and red area that partially overlays the Clipper (1).

Both the line and area Candidates are split where they cross the Clipper boundary, and the results are output:

(3) Portions of Candidates that fall Inside the Clipper (red only)
(4) Portions of Candidates that fall Outside the Clipper (red only)

Raster Clipping, Alpha and Nodata

If Raster Candidates > Add Alpha/Nodata is set to Yes, cells that fall outside the clip area but within the resulting bounding box will be assigned values as follows:

Bands with a Nodata value assigned: Nodata value
Bands without a Nodata value assigned:
- RGB : Alpha band is added, all bands set to 0, resulting in transparent cells.
- Bands with palettes: Nodata value is added, set to Nodata value.
- Bands without palettes: Set to 0.

To set an explicit value for Nodata, use the RasterBandNodataSetter transformer prior to the Clipper.

This transformer is unaffected by raster band and palette selection.

Examples

Example: Raster clipping - area on rasters

In this example, we have a series of orthophoto tiles, which we would like to clip to the city’s land boundary. The boundaries (extents) of each raster are overlaid in orange.

The boundary - a single polygon - is connected to the Clipper input port, and the series of TIFF images are connected to the Candidate port.

In the Clipper parameters dialog, Multiple Clippers is set to No, which will improve performance in this case, where we do have a single Clipper area.

For a raster clipping operation, the only other parameters we need to look at are Raster Candidates.

Setting Preserve Raster Extents to No will clip partial rasters as tightly as possible (while still maintaining a rectangular boundary). Add Alpha/Nodata as Yes will add a transparency layer where cells fall outside the irregular clip boundary but inside the raster extents.

Of the 40 rasters that went in, 32 of them fell partially or entirely Inside the clip boundary. In the rasters that intersected the boundary, cells that fall inside are untouched. Cells that fall outside have all bands set to 0 - including the added alpha band, indicating transparency.

This close-up shows the clipping of pixels along the water boundary.

The extents of new rasters are shown here in orange. They are of varying size now, clipped tightly to the Clipper boundary (as we chose not to Preserve Raster Extents).

Usage Notes

Memory requirements: Clipping rasters can fail if not enough memory is available, which is more likely to happen the larger the raster is. If this occurs, increasing available memory or reducing raster resolution may help.

Choosing a Spatial Transformer

Many transformers can assess spatial relationships and perform spatial joins - analyzing topology, merging attributes, and sometimes modifying geometry. Generally, choosing the one that is most specific to the task you need to accomplish will provide the optimal performance results. If there is more than one way to do it (which is frequently the case), time spent on performance testing alternate methods may be worthwhile.

To correctly analyze spatial relationships, all features should be in the same coordinate system. The Reprojector may be useful for reprojecting features within the workspace.

Spatial Transformers Comparison Matrix

Transformer	Can Merge Attributes	Alters Geometry	Counts Related Features	Creates List	Supported Types*	Recommended For
SpatialFilter	Yes	No	No	No	Point Text Curve Area	Testing for the existence of spatial relationships between two sets of features, and routing them according to whether they pass or fail the test(s).
SpatialRelator	Yes	No	Yes	Yes	Point Text Curve Area	Identifying the nature of spatial relationships between two sets of features.
AreaOnAreaOverlayer	Yes	Yes	Yes	Yes	Area	Finding polygon overlaps and extracting them into new geometry.
LineOnAreaOverlayer	Yes	Yes	Yes	Yes	Curve and Area	Finding intersections between lines and polygons, and splitting the lines where they intersect with the polygons.
LineOnLineOverlayer	Yes	Yes	Yes	Yes	Curve	Finding intersections between line features, splitting them, and generating new line geometry as well as points representing the intersections.
PointOnAreaOverlayer	Yes	No	Yes	Yes	Point and Area Text and Area	Identifying points that fall within polygons, and merging attributes between them
PointOnLineOverlayer	Yes	Yes	Yes	Yes	Point and Curve Text and Curve	Identifying where points fall on lines, and splitting the lines into new geometry.
PointOnPointOverlayer	Yes	No	Yes	Yes	Point Text	Identifying points in the same location (within a tolerance), and merging attributes between them.
Intersector	Yes	Yes	Yes	Yes	Point Text Curve Area	Finding intersections between all input features, regardless of geometry (including self-intersections), splitting features, and creating new geometry.
Clipper	Yes	Yes	No	No	Point Text Curve Area Surface Solids Raster Point Cloud	Comparing features against a set of Clipper features, and splitting the features at or along the Clipper boundaries. Outputs both new and untouched geometry, identified as either Inside or Outside the Clipper.
NeighborFinder	Yes	In some cases	No	Yes	Point Text Curve Area	Identifying the nearest other feature(s) to each feature being considered, either in another set of features or within the same feature set.
TopologyBuilder	Yes	Yes	No	Yes	Point Text Curve Area	Analyzing spatial relationships between features to compute topology, splitting features and creating new geometry representing topologically significant nodes, edges, and faces, with associated attributes.

* Note that Curve includes Lines, Arcs, and Paths. Area includes Polygons, Donuts, and Ellipses.

Configuration

Input Ports

Output Ports

Parameters

Group Processing

Group By

The default behavior is to use the entire set of features as the group. This option allows you to select attributes that define which groups to form.

Note that when using Group By, if a Candidate has no equivalent Clipper, the feature is output unclipped via the Outside output port, with the attribute _fme_no_clipper = Yes.

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.

General

Multiple Clippers	Yes: All Clipper features will be used. No: Only a single Clipper feature will be used.
Clippers Arrive First	Yes: The Clipper assumes that all Clipper features will enter the transformer before any Candidate features. Any further Clipper features that arrive after the first Candidate will be rejected. No: The Clipper makes no assumptions about the order of Candidates and Clippers features. Clippers are processed regardless of their relative order with Candidates.
Overlapping Clippers	Controls how candidates get clipped when there are multiple clippers that overlap each other. Clip Interim Results: Each clipper feature will clip the interim results (both inside and outside) produced by the previous clipper feature’s interaction with all the candidates. The part of a candidate that’s outside of all clippers will be output from the outside port. This option allows for each output piece to acquire the attributes from each of the Clipper features they were clipped by. Clip Original Candidates: Each clipper feature will clip the original form of a candidate. Their intersection will be output via the inside port. The part of a candidate that’s outside of all clippers will be output from the outside port. Clip Only Outside Remainders: Each candidate will be clipped by the first clipper, then the part that’s outside of the first clipper will be clipped by the second clipper, and so on. The part of a candidate that’s outside of all clippers will be output from the outside port. Note Because Clippers are applied to Candidates in the same order that they arrive at the factory, ordering Clippers by their likelihood to contain candidates may improve performance.
Candidates on Clipper Boundary	This parameter directs what action should be taken with Candidate features that lie entirely on the boundary of the clipper. Output as Inside: The features that lie on the boundary are output via the Inside port. Output as Outside: The features that lie on the boundary are output via the Outside port. Output as Inside and Outside: The features that lie on the boundary are duplicated and output as both Inside and Outside.
Invalid Parts Handling	Reject Parts Only: Only parts in a multi/aggregate feature that are invalid as input (Clipper or Candidate) will be rejected. The rest of the feature will remain aggregated and continue to be processed. Feature hierarchy will be maintained with the rejected parts as much as possible. Reject Whole Feature: When a feature contains parts that are invalid as input (Clipper or Candidate), the whole feature will be rejected.

Area on Area Z Values

Preserve Z From

Specifies where to take the measures and Z values from when Clippers and Candidates are both areas.

Candidate Only: All Z values of Clippers will be dropped.

Clipper Only: All Z values from Candidates that intersect the Clippers will be dropped.

Clipper and Candidate: Measures and Z values from the Candidate and Clipper are used. The Connect Z Mode parameter will determine how z values are handled.

Note Clipper Z values and measures are not preserved when clipping curves (lines) with areas.

Missing Z Values

Specifies how to deal with geometries that have z values, but are missing at least one value.

Planar Interpolation: Depending on the option selected for “Preserve Z From” parameter, input candidate or clipper areas are temporarily interpreted as surfaces, and Z values on new vertices are determined by interpolation using that temporary surface.

Linear Interpolation: Use the Z values from adjacent vertices to perform a linear interpolation to determine the missing Z value

Custom Value: Use the value specified in this parameter on any vertices with a missing Z value.

None (Drop Values): If an output feature has missing Z values on any vertices, all Z values are dropped. If an output feature has Z values on all vertices, all Z values are preserved.

Connect Z Mode

If applicable, select a method for handling z values.

To specify how (and if) paths should be closed in 3D, select a mode.

Extend	The Curve is extended so that all vertices are left at their original location.
Average	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is the average of the original two.
Snap to Single Vertex	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is taken from one of the encountered vertices.
Ignore	Z values are ignored. No change is made to the way the nodes are connected.

Measures

Preserve Measures From

Specifies where to take the measures from.

Candidate Only: All measures of the Clippers will be dropped.

Clipper Only: All measures from the Candidates that intersect the Candidate will be dropped.

Clipper and Candidate: Measures from the Candidate and Clipper are used.

Note Clipper measures are not preserved when clipping curves (lines) with areas.

Missing Measure Values

Specifies how to deal with geometries that have measures, but are missing at least one value.

Linear Interpolation: Use the measure values from adjacent vertices to perform a linear interpolation to determine the missing measure value.

Neighboring Vertex: Copy the measure value from a neighboring vertex.

Custom Value: Use the value specified in this parameter on any vertices with a missing measure value.

None (Drop Values): If an output feature has missing measure values on any vertices, all measure values are dropped. If an output feature has measure values on all vertices, all measure values are preserved.

Raster Candidates

Preserve Candidate Extents

If this parameter is set to No, the Inside rasters which were clipped will be equal to the intersections of the Clippers and Candidates. Otherwise, the intersections will be padded so that the extents are identical to those of the input rasters.

Determine Cell Location By

Bounds: Cells whose bounds are completely inside a clipper are considered “inside.” Cells whose bounds are completely outside a clipper are considered “outside.” Cells whose bounds are partially inside a clipper and partially outside a clipper are considered on the Clipper Boundary and will be output based on the Candidates on Clipper Boundary setting.

Centers: Cells whose centers are inside a clipper are considered “inside.” Cells whose centers out outside a clipper are considered “outside.” Cells whose centers are on a Clipper Boundary will be output based on the Candidates on Clipper Boundary setting

Add Alpha/Nodata

If Yes, either an alpha band with transparency or Nodata values will be applied outside clip boundaries, as appropriate.

Attribute Accumulation

Merge Attributes

When enabled, attributes on the Clipper will be merged onto the Candidate as defined by the parameters here. Otherwise, no attribute merging will take place.

If attributes on the Clipper and Candidate features share the same name, but are not geometry attributes that start with fme_, then they are deemed conflicted.

Accumulation Mode

Merge Clipper: The Candidate feature will retain all of its own un-conflicted attributes, and will additionally acquire any un-conflicted attributes that the Clipper feature has. This mode will handle conflicted attributes based on the Conflict Resolution parameter.

Prefix Clipper: The Candidate feature will retain all of its own attributes. In addition, the Candidate will acquire attributes reflecting the Clipper feature’s attributes, with the name prefixed with the Prefix parameter.

Only Use Clipper: The Candidate feature will have all of its attributes removed, except geometry attributes that start with fme_. Then, all of the attributes from one (arbitrary) Clipper feature will be placed onto the Candidate.

Conflict Resolution

Use Candidate: If a conflict occurs, the Candidate values will be maintained.

Use Clipper: If a conflict occurs, the values of the Clipper will be transferred onto the Candidate.

Prefix

If the Accumulation Mode parameter is set to Prefix Clipper, this value will prefix attributes that are being added to the Candidate feature from the Clipper feature.

Generate List From Overlapping Clippers

When enabled, adds a list attribute to the output features, and the attributes of containing Clipper features are added to the list. Candidates will receive list attributes from all containing Clipper features.

Clipper List Name

Enter a name for the list attribute.

Note List attributes are not accessible from the output schema in FME Workbench unless they are first processed using a transformer that operates on them, such as ListExploder or ListConcatenator. Alternatively, AttributeExposer can be used.

Add To List

All Attributes: All attributes will be added to the output features.

Selected Attributes: Enables the Selected Attributes parameter, where specific attributes may be chosen to be added.

Selected Attributes

Enabled when Add To List is set to Selected Attributes. Specify the attributes you wish to be added.

Advanced

Preserve Feature Order

This parameter controls the order in which features exit a transformer.

When a transformer has more than one output port, features usually exit one port at a time. At times, it may be useful to keep the order that features arrived in, switching from port to port as necessary. This allows feature order to be preserved, though at a potential cost in processing efficiency.

Select a method for feature ordering.

Per Output Port (Default)

Only preserve the input order of features as they occur within the group of features exiting a given output port.

All features exiting an output port retain their ordering relative to each other (within the group), but not relative to features exiting other output ports.

This option is generally the most efficient, where large chunks of features will exit an output port together (taking advantage of bulk mode).

As features exiting different output ports may not be strictly output in the order they arrived, output ordering may be unpredictable.

Across Output Ports

Strictly preserve the input order of features, regardless of which output port they exit. Features will be output singly in the same order they arrived, switching from port to port as necessary. This option is generally less efficient as the processing gains of bulk mode are less likely to apply - however, feature order is predictable.

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.

How to Set Parameter Values

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

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

Table Tools

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.

Reference

Processing Behavior	Group-Based
Feature Holding	Yes
Dependencies
Aliases
History

FME Community

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Examples may contain information licensed under the Open Government Licence – Vancouver and/or the Open Government Licence – Canada.