Clipper

Performs a geometric clipping operation (sometimes called a cookie cutter). Most geometry types can be clipped by an area, and some may also be clipped by a solid. 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, which will be overlaid on other features to identify which of those features fall inside or outside the Clippers, and split those features 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.
Clippees, 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).
Clippee 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 new Clipped Indicator Attribute (default name _clipped), which is set to “yes” for features that have been segmented, enabling differentiation between features that were wholly inside or outside the clip boundaries and those that intersected the Clipper feature(s) and so were modified.

The Clipper works on many 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 Clippees, a red line that crosses the Clipper (1), and red area that partially overlays the Clipper (1).

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

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

What can I clip?

As the Clipper collects multiple clipping methodologies into one convenient transformer, it is important to understand which type of clipping you wish to perform, and which types of geometry can be compared in a clipping operation.

Most types can be clipped by an area or multi-area. Some types can also be clipped by a solid or multi-solid.

If the clipping operation you need is not listed here, consider one of the Overlayers or the Intersector- see Choosing a Spatial Transformer below.

Clipper Geometry Support Reference

This:	Can be clipped by:	Can clip:
Point/text	Area* Solid**	Nothing
Curve/line	Area*	Nothing
Area	Area*	Point/text Curve/line Area Solid Point Cloud Raster Multi/aggregates of the above
Surface	Nothing	Nothing
Solid	Area* Solid**	Point/text Solid Point Cloud Multi/aggregates of the above
Point cloud	Area* Solid**	Nothing
Raster	Area*	Nothing
Multi-point/aggregate	Area* Solid**	Nothing
Multi-curve/aggregate	Area*	Nothing
Multi-area/aggregate	Area*	Point/text Curve/line Area Solid Point Cloud Raster Multi/aggregates of the above
Multi-solid/aggregate	Area* Solid**	Point/text Solid Point Cloud Multi/aggregates of the above
No geometry	Nothing	Nothing

* Area as Clipper: includes polygons, ellipses, donuts, and aggregates (multi-) of them.

** Solid as Clipper: includes solids and aggregate (multi-) solids.

Examples

Example: Raster clipping - area on rasters

In this example, we have a series of 40 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 Clippee port. Note that 40 individual TIFF files are read in, but only 32 will be sent out the Inside output port.

In the Clipper parameters dialog, we set Clipper Type to Single Clipper, which will improve performance in this case, where we do have only one Clipper area.

For a raster clipping operation, the only other parameters we need to look at are Raster Parameters, where we choose whether or not we want areas outside the clip boundary to be padded with Nodata pixels to their original extents. No is the default, and fine for this case. (If you want the output rasters to retain their original dimensions, you would choose Yes.)

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, pixels that fall inside are untouched, but pixels that fall outside are set to Nodata - indicated here by black.

This close-up shows the clipping of pixels (Nodata - black) 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 Clippee Extents).

Usage Notes

Because a raster feature must always be rectangular, clipped raster cells (that is, those outside the clipper but part of an Inside raster) will be set to the Nodata value. If a Nodata value has not been set, clipped raster cells will be set to 0. To set a value for Nodata, use the RasterBandNodataSetter transformer prior to the Clipper.
This transformer is unaffected by raster band and palette selection.
A feature can be clipped multiple times, but not iteratively (for example, if a line passes through two overlapping polygons, you don’t get a separate clipped line for the overlap - just one per polygon).

For maximum intersectionality, consider the Intersector.

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 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: 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 Clippee has no equivalent Clipper, the feature is output unclipped via the Outside output port, with the attribute _fme_no_clipper = Yes.

Group By Mode

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process 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.

Z and Measures Parameters

Preserve Measures/Z From

Specifies where to take the measures and Z values from.

Clippee Only: All measures and Z values of the Clipper will be dropped.

Clipper Only: All measures and Z values from the Clippee will be dropped.

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

Connect Z Mode

If applicable, select a method for handling z values.

Connect Z Mode

When viewed in 2D (ignoring Z), a path (which may define the border of a polygon) may appear to be closed as shown in the left figure below. This same path, when viewed in 3D, may appear to be open as shown in the right figure below.

To specify how (and if) paths should be closed in 3D, select one of the listed modes.

Mode	Description	Example
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.
First Wins	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 the first encountered vertex.
Last Wins	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 the last encountered vertex.
Ignore	Z values are ignored. No change is made to the way the nodes are connected.

Measures/Z Conflict Value

This parameter specifies how to deal with geometries that have a measure, but are missing at least one value, or that have z values, but are missing at least one value.

None (Drop Values): Remove incomplete measures or z values.

Compute: Look at the values on either side of the missing value, and compute an estimate.

Custom Value: The missing values are filled in with the specified custom default value.

Treat Measures as

When using the Compute mode to compute missing measure values, measures can be considered Continuous, and linearly interpolated from their neighbors, or they can be Discrete, and taken exactly from the nearest neighbor.

Vector Parameters

Tolerance

The minimum distance between geometries in 2D before they are considered equal, in ground units. If the tolerance is None, the geometries must be exactly identical to be considered equal. If the tolerance is Automatic, a tolerance will be automatically computed based on the location of the input geometries. Additionally, a custom tolerance may be used.

Clippees on Clipper Boundary

This parameter directs what action should be taken with Clippee features that lie entirely on the boundary of the clipper.

Treat as Inside: These features that lie on the boundary are output via the Inside port.

Treat as Outside: These features that lie on the boundary are output via the Outside port.

Treat as Inside and Outside: Points and line segments on the boundary are duplicated and output as both Inside and Outside.

Preserve Lines as Path Segments

Yes: Contiguous lines that constitute the boundary of the output features will be left as separate segments in a path.

No: Such lines will be joined into longer lines in the output unless they have different properties (for example, traits, measures, and geometry name).

Merge Attributes

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

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

Accumulation Mode

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

Only Use Clipper: The Clippee 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 Clippee.

Conflict Resolution

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

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

Prefix

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

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.