FME Transformers: 2024.1

Categories
3D

3D

Point Clouds

Point Clouds

Categories
3D

3D

Point Clouds

Point Clouds

DEMGenerator

Constructs a Delaunay triangulation based on input points and breaklines. That triangulation is then uniformly sampled to produce a digital elevation model (DEM points).

Usage Notes

  • Use the RasterDEMGenerator if a DEM is destined to be sent to a raster format, or if further raster processing is required.

  • To build a TIN (triangulated irregular network) surface from points, lines, and/or rasters, see the TINGenerator and SurfaceModeller.

Configuration

Input Ports

These input features may be 2D or 3D. Other than points, lines and area geometries, they may also be raster, point cloud, and aggregate geometries.

2D features will be forced to 3D by adding a z value of 0. In most cases, all points extracted from this port will be found in the vertex pool of the underlying surface model. A minimum of 3 unique points are required to construct a surface model. Points with duplicate x and y values will be dropped.

These input features may be 2D or 3D, and may reside inside an aggregate structure.

2D features will be forced to 3D by adding a z value of 0. Breakline edges will be found in the edge pool of the underlying surface model. Sometimes, a breakline edge will be split up to allow an optimal triangulation of the surface model. Points with duplicate x and y values will be dropped.

Output Ports

This output port samples the underlying surface model according to the sampling rates specified in Output DEM X Cell Spacing, and Output DEM Y Cell Spacing, and produces a set of evenly spaced 3D points.

Parameters

Group By

This parameter allows groups to be formed by attribute values. Zero or more attributes may be specified.

Input features with the same attribute values are placed into the same group. The transformer then operates independently on each group of input features.

If this parameter is left blank, the transformer will treat the entire set of input features as one group.

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.

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.

Surface Tolerance

This parameter is used to determine which input points to add to the surface model as vertices. Specifying a value of 0 turns off vertex filtering.

Tip: A larger value will speed up surface model construction. The larger the value, the more input points will be filtered out. For input files with millions – or even billions – of points, it becomes essential to increase this value.

When a positive value for surface tolerance is specified, it works as follows. For each vertex that is being added to the model:

  • If the x,y location is outside the 2D convex hull of the existing surface model, it is added to the model.
  • If the x,y location is inside the 2D convex hull of the existing surface model:
    • The difference between the z value from the existing surface model and the z value of the vertex is calculated.
    • This difference is compared to the surface model tolerance.
    • The vertex is only added to the surface model if the difference is greater than the surface tolerance; otherwise, the vertex is discarded.

Breakline Method

Select the way in which breaklines will affect the triangulation if their edges would violate the Delaunay condition, which helps to prevent narrow triangles.

Preserve Delaunay by Adding Points

(Default) The triangulation will fully satisfy the Delaunay condition, although input breakline edges may be subdivided by adding points.

For breakline edges which do not naturally appear in the triangulation, points will be added where it intersects with other triangulation edges. Those points will have their elevation determined by interpolation along the breakline edge.

Due to floating point precision, the subdivided edges may deviate from the original breakline edge. Breakline Tolerance limits this deviation.

Preserve Breakline Edges

Input breakline edges will appear directly in the triangulation, although triangles around those edges may violate the Delaunay condition.

The triangulation will fully satisfy a weakened version of the Delaunay condition which allows for points to be within a triangle’s circumcircle, so long as a breakline edge blocks visibility of that point from the triangle.

Breakline Tolerance

When Breakline Method is Preserve Delaunay by Adding Points , select or specify a tolerance value, which is the maximum distance that subdivided edges may deviate from the input breakline edge.

Smaller values will make the representation of breaklines more accurate, but may require the addition of many points in cases where breakline edges are nearby one another.

Automatic calculates an appropriate tolerance for the input geometry, and is generally recommended.

A Custom Value may be entered, but must be greater than zero and greater than the Automatic value.

See Geometry Concepts > Tolerance.

Interpolation Method

This parameter is used for the output ports DEMPoints and DEMRaster when these output ports exist on the transformer. It is also used if DrapeFeatures are input to the model.

  • AUTO: The transformer will calculate each output point automatically. The PLANAR method is used if the output point is within a surface triangle in xy and the CONSTANT method is used otherwise.
  • PLANAR: Barycentric interpolation is used to determine the z value for each output point. If an output point is outside the 2D convex hull of the surface model, the output z value will be set to NaN (Not a Number).
  • CONSTANT: The z value of each output point is set to the z value of the closest vertex in the underlying model.

Elevation

Name the parameter to contain elevation values for the output ports Contours and DEMPoints, when these output ports exist on the transformer.

DEM X Cell Spacing

Name the attribute to contain cell spacing values on the x-axis.

DEM Y Cell Spacing

Name the attribute to contain cell spacing values on the y-axis.

Editing Transformer Parameters

Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click beside the applicable parameter.

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.

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.

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.

For more information, see Transformer Parameter Menu Options.

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 all results about the DEMGenerator on the FME Community.

 

Keywords: pointcloud