PointCloudSorter

In this example, we will use point cloud sorting to identify the lowest points in a point cloud, removing vegetation to produce a bare earth representation of the area.

Note that the source point cloud is a heavily forested area, shown here from an oblique angle in the FME Data Inspector, and the highest point is 145.92 meters.

We will use three steps to find the lowest points:

1. Round the x and y coordinates to a chosen grid size with a PointCloudExpressionEvaluator,
2. Sort the points by elevation with a PointCloudSorter, in ascending order, so the lowest points occur first, and
3. Merge the point cloud with itself to isolate the lowest point at each location, using a PointCloudMerger.

Step 1 - Round the coordinates

The point cloud is first routed into a PointCloudExpressionEvaluator. In the parameters dialog, the x and y components are recalculated, using an expression that rounds them to a specific interval - in this case, 10 meters.

Step 2 - Sort the points by elevation

Next, the point cloud is sent to a PointCloudSorter. In the parameters dialog, we sort based on the z component, in Ascending order.

The result of these first two transformers is a point cloud that still contains all original points, but they have been shifted onto a regular xy grid with 10 meter spacing, and internally, the points occur in ascending order of elevation and so will subsequently be processed in that order.

Step 3 - Isolate the lowest points

Next, the sorted point cloud is merged onto itself in a PointCloudMerger, routing a copy into both the Requestor and Supplier input ports.

The Referenced output port produces a point cloud containing the first occurrence of any given x,y pair. Since the lowest ones will be processed first due to the sorting, those are the points that will be kept.

(See the PointCloudMerger for a complete example of removing duplicates in a point cloud.)

In the parameters dialog, we join on the x and y components only - not z.

After sending the Referenced point cloud through a PointCloudPropertyExtractor (not shown in the workspace above) to calculate its new x, y, and z extents, we can see the bare earth representation as points spaced 10 meters apart, and with a new maximum elevation of 98.28 meters.

This transformer accepts only point cloud features.

Point cloud features with points sorted according to parameter selections.

Non-point cloud features will be routed to the <Rejected> port, as well as invalid point clouds.

Rejected features will have an fme_rejection_code attribute with one of the following values:

INVALID_GEOMETRY_TYPE

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.

This table specifies the components by which the point cloud will be sorted.

Sorting is done in the order specified. That is, all points will be sorted by the values of the first component in the list. If there are any ties, they will be broken by the values of the second component, then the third component, and so on.

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.

Table Tools

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

Note: Not all tools are available in all transformers.