Replaces the geometry of the feature with a polygon representing its hull.
Example
Usage Notes
- Point Clouds: the HullReplacer does not consider individual points within a point cloud feature, and will produce the equivalent to a bounding box. To generate a hull from point cloud points, use a PointCloudToPointCoercer prior to the HullAccumulator, setting the Output Geometry parameter to either Single Multipoint or Individual Points.
Configuration
Input Ports
Input
This transformer accepts both 2D and 3D features, but the z coordinates of 3D features will be ignored during the calculation of the hull. Depending on the value of the Output parameter, the convex hull of 3D features may be a polygon that uses unmodified 3D vertices from the input features. This may result in a polygon with varying z coordinates.
Arcs and ellipses will be stroked prior to the calculation of the hull. Text features will be treated as points.
Output Ports
Hull
A feature representing the requested hull. Typically a polygon, but possibly a line or a point.
<Rejected>
Features with non-numeric attributes for Alpha and Default Z Value
Rejected features will have an fme_rejection_code attribute with one of the following values: INVALID_GEOMETRY_VERTICES, INVALID_PARAMETER_ALPHA_VALUE, INVALID_PARAMETER_DEFAULT_Z_VALUE.
Parameters
Hull
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Hull Type |
The Hull Type parameter can specify either a convex or a concave hull. A convex hull is a polygon where no interior angle is greater than 180 degrees. For a concave hull this restriction does not apply. The convex hull is defined as the minimum enclosing convex polygon. In lay terms, the effect is similar to tightening a rubber band around the feature. Note that the convex hull may be a line or a point if the resulting polygon has an area of zero. The concave hull, also known as the alpha hull, is calculated based on the Alpha Value parameter. It is possible for the concave hull to more closely represent the outline of a feature’s geometry than the convex hull can. The concave hull may consist of multiple donuts or polygons. |
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Alpha Value |
When the Alpha Value parameter is specified, it is used in the alpha hull calculation directly; a larger number will generally produce larger areas. If a circle with a radius of Alpha Value ground units is able to pass between two points A and B of the feature without touching any other points of the feature, then the resulting hull will not directly connect A and B. Geometries that are farther away than Alpha Value from the rest of the geometries may be culled (removed) if they do not constitute a valid area on their own. It is possible that a null geometry will be returned if the specified alpha was too small for the spacing of the geometry. When the Alpha Value parameter is not specified or is set to 0, an approximation to the optimal alpha, which is the smallest alpha that generates a single area, will be used to generate the concave hull. Concave hull generation works best with points, but line and area geometries will be accepted and converted to points if input. |
Output Dimension
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Output |
Choose between 2D and 3D representation of coordinates of points in the hull. When 2D is chosen, all z coordinates will be removed from any vertices in the output. When 3D is chosen, the convex hull will be a polygon that uses unmodified 3D vertices from the input features. If there is a mixture of 2D and 3D vertices in the input features, then the 2D vertices will be converted to 3D using the specified Default Z Value. However, if all input features are 2D, the output will not be converted to 3D. When Automatic is chosen, the output will be similar to choosing 3D, except that for a mixture of 2D and 3D vertices, the 2D vertices will be converted to 3D using the largest z value from the input features. |
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Default Z Value |
2D vertices that are converted to 3D will use the Default Z Value as the z coordinate when the Output parameter is 3D. |
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.
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.
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
| These functions manipulate and format strings. | |
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Special Characters |
A set of control characters is available in the Text Editor. |
| Math functions are available in both editors. | |
| Date/Time Functions | Date and time functions are available in the Text Editor. |
| These operators are available in the Arithmetic Editor. | |
| These return primarily feature-specific values. | |
| 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
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Row Reordering
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Enabled once you have clicked on a row item. Choices include:
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Cut, Copy, and Paste
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Enabled once you have clicked on a row item. Choices include:
Cut, copy, and paste may be used within a transformer, or between transformers. |
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Filter
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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. |
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Import
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Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers. |
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Reset/Refresh
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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.
Transformer History
This transformer was previously named ConvexHullReplacer.
FME Community
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Keywords: ConvexHullCreator ConvexHullReplacer