RasterDEMGenerator

Produces a raster digital elevation model (DEM) by uniformly sampling a Delaunay triangulation generated from input points and breaklines.

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Typical Uses

Creating raster elevation models from non-gridded features such as contours or point clouds.

How does it work?

The RasterDEMGenerator receives input features, triangulates a surface based on them, and then outputs a raster DEM with elevation values sampled from the surface at a specified regular interval. The output raster will contain a single numeric band, of the interpretation type Real64.

The input features are discarded.

Input features can be of a variety of types, including points, lines, areas, rasters, and point clouds. Aggregate geometries are supported, and multiple input features and types may be combined to produce one raster DEM output feature.

There are two input ports - Points/Lines and Breaklines. At least one input feature must be provided, which may be routed into either of these ports.

Input features may be either 2D or 3D - however, 2D features will be forced to 3D with an elevation (z value) of zero (0). If the source dataset’s z values are not stored as z coordinates (for example, contours with elevation stored as an attribute), a 3DForcer transformer may be used to convert them to a z coordinate prior to entering the RasterDEMGenerator.

A choice of breakline handling and interpolation methods is available. Surface tolerance and cell spacing may be adjusted, and a Nodata value may be defined.

This transformer is unaffected by raster band and palette selection.

Examples

Example: Generating a raster DEM from contours with an elevation attribute

In this example, we will generate a DEM from a set of contour lines, spaced at a ten meter interval. Note that the source data does not have elevation values as a z coordinate - though it is a 3D dataset, the z values are all zero (0).

The elevation values are stored as an attribute named ELEVATION and need to be applied as z values before the DEM is generated.

The contours are routed first into a 3DForcer, and then to the RasterDEMGenerator.

In the 3DForcer parameters dialog, Elevation is set to the ELEVATION attribute, and Preserve Existing Z Values is set to No. The attribute values will overwrite the existing z values.

Next, in the RasterDEMGenerator’s parameters dialog, we set Surface Tolerance to zero (0), which means that no vertex filtering will take place, and all points will be considered.

Cell Spacing (both X and Y) is set to 10. The output cells will be 10 meters square, as the source data’s coordinate system is in meters.

The output DEM raster has a single Real64 band, 10 meter square cells, and the specified Nodata value.

Usage Notes

If input features’ elevation values are not stored as Z coordinates, use a 3DForcer prior to the RasterDEMGenerator.
To produce individual elevation points instead of a raster, consider using the DEMGenerator.
To build a TIN (triangulated irregular network) surface from points, lines, and/or rasters, see the TINGenerator and SurfaceModeller.
When processing large input datasets, increasing the Surface Tolerance may provide performance gains, but may reduce accuracy.
For more complex elevation modelling tasks, such as including contour generation, accessing components of the underlying surface model, feature draping, or creating multiple representations of a surface model, consider using the SurfaceModeller.

Choosing a Raster Transformer

FME has an extensive selection of transformers for working with raster data. They can be generally categorized as working with whole rasters, bands, cells or palettes, and those designed for workflow control or combining raster with vector data.

For information on raster geometry and properties, see Rasters (IFMERaster).

Raster Transformers

Working with Rasters

These transformers generally apply to whole rasters.

RasterCellOriginSetter	Sets the cell origin point within cells in a raster.
RasterConvolver	Applies a convolution filter (sometimes called a kernel or lens) to raster features and outputs the results.
RasterDiffuser	Enhances the features of a raster image. The RasterDiffuser enhances the borders, lines, and curves while reducing noise in the flat areas of the raster image.
RasterExpressionEvaluator	Evaluates expressions on each cell in a raster or pair of rasters, including algebraic operations and conditional statements.
RasterExtentsCoercer	Replaces the geometry of input raster features with a polygon covering either the extents of a raster or the extent of data within a raster.
RasterGCPExtractor	Extracts Ground Control Point (GCP) coordinate system and point values from a raster feature and exposes them as attributes.
RasterGCPSetter	Sets Ground Control Points (GCPs) on a raster, pairing cell positions with known coordinates.
RasterGeoreferencer	Georeferences a raster by either known corner coordinates or origin, cell size, and rotation.
RasterHillshader	Generates a grayscale shaded relief representation of terrain, based on elevation values.
RasterInterpretationCoercer	Alters the interpretation type of rasters, including all bands, and converts cell values if necessary.
RasterMosaicker	Merges multiple raster features into a single raster feature.
RasterPropertyExtractor	Extracts the geometry properties of a raster feature and exposes them as attributes.
RasterPyramider	Resamples rasters to multiple resolutions, based on either number of levels or dimensions of the smallest output raster.
RasterRegisterer	Transforms an image to minimize its difference with another.
RasterResampler	Resamples rasters, based on specified output dimensions, cell size in ground units, or percentage of original, and interpolates new cell values.
RasterRotationApplier	Rotates a raster feature according to its rotation angle property, interpolating new cell values, updating all other affected raster properties, and producing an output raster feature with a rotation angle of zero.
RasterSubsetter	Clips raster features using pixel bounds instead of ground coordinates, and optionally adds cells around the perimeter.
RasterTiler	Splits each input raster into a series of tiles by specifying either a tile size in cells/pixels or the number of tiles.
RasterToPolygonCoercer	Creates polygons from input raster features. One polygon is output for each contiguous area of pixels with the same value in the input raster.
WebMapTiler	Creates a series of image tiles that can be utilized by web mapping applications such as Bing™ Maps, Google Maps™, or Web Map Tile Service. This is done by resampling rasters to various different resolutions and then splitting them into tiles.

Working with Bands

These transformers generally apply to bands.

RasterBandAdder	Adds a new band to a raster feature.
RasterBandCombiner	Merges coincidental raster features into a single output raster feature, preserving and appending all bands.
RasterBandInterpretationCoercer	Alters the interpretation type of individual raster bands, converting cell values if necessary.
RasterBandKeeper	Removes all unselected bands from a raster feature.
RasterBandMinMaxExtractor	Extracts the minimum and maximum band values, palette keys, and palette values from a raster feature, and adds them to a list attribute.
RasterBandNameSetter	Sets the band name of selected bands on a raster, making raster contents simpler to understand compared to band numbers.
RasterBandNodataRemover	Removes the existing Nodata identifier from selected bands of a raster feature. Any values previously equal to the Nodata value are considered valid data.
RasterBandNodataSetter	Sets a new Nodata value on selected bands of a raster feature.
RasterBandOrderer	Specifies the required order of bands in a raster. Bands are reordered according to the input band indices.
RasterBandPropertyExtractor	Extracts the band and palette properties of a raster feature and exposes them as attributes.
RasterBandRemover	Removes any selected bands from a raster feature.
RasterBandSeparator	Separates bands or unique band and palette combinations, and outputs either individual raster features or a single new raster feature containing all combinations.
RasterStatisticsCalculator	Calculates statistics on raster bands and adds the results as attributes.

Working with Cells

These transformers generally apply to individual cells.

RasterAspectCalculator	Calculates the aspect (direction of slope) for each cell of a raster. Aspect is measured in degrees from 0 to 360, clockwise from north.
RasterCellCoercer	Creates individual points or polygons for each cell in a raster, optionally extracting band values as z coordinates or attributes.
RasterCellValueCalculator	Evaluates basic arithmetic , minimum, maximum or average operations on the cell values of a pair of rasters.
RasterCellValueReplacer	Replaces a range of band values in a raster with a new single value.
RasterCellValueRounder	Rounds off raster cell values.
RasterSegmenter	Partitions a raster image into arbitrarily sized groups of cells from the input image based on intensity differences in the input raster image cells.
RasterSingularCellValueCalculator	Performs basic arithmetic operations on the cell values of a raster against a numeric value.
RasterSlopeCalculator	Calculates the slope (maximum rate of change in z) for each cell of a raster.

Working with Palettes

These transformers generally apply to palettes.

RasterPaletteAdder	Creates a palette from an attribute, and adds this palette to all selected bands on a raster.
RasterPaletteExtractor	Creates a string representation of an existing palette on a raster and saves it to an attribute.
RasterPaletteGenerator	Generates a palette out of the selected band(s) of a raster. The output raster will have the selected band(s) replaced by a new band with a palette.
RasterPaletteInterpretationCoercer	Alters the interpretation type of raster palettes.
RasterPaletteNodataSetter	Identifies the palette key that matches a raster band’s Nodata value, and sets a value on it.
RasterPaletteRemover	Removes selected palette(s) from raster features.
RasterPaletteResolver	Resolves the palette(s) on a raster by replacing cell values with their corresponding palette values. Palette values with multiple components, such as RGB, are broken down and the individual values assigned to multiple, newly-added bands.

Workflow Control

These transformers generally control the flow of features in a workspace.

RasterCheckpointer	Forces accumulated raster operations to be processed, saving the state to disk and releasing resources to tune performance or assist with memory limitations.
RasterConsumer	Reads raster features for testing purposes, including any accumulated raster operations. No additional operations are performed, and nothing is done with the features.
RasterExtractor	Serializes the geometry of a raster feature into a Blob attribute, encoding the contents according to a choice of common binary raster formats.
RasterNumericCreator	Creates a numeric raster of specified size and resolution, with default cell values.
RasterReplacer	Decodes a binary attribute containing encoded rasters stored as Blobs, replacing the feature’s geometry with the decoded raster.
RasterRGBCreator	Creates a color raster feature of specified size, resolution, and interpretation type, with default cell values.
RasterSelector	Selects specific bands and palettes of a raster for subsequent transformer operations.

Vectors and Rasters

These transformers generally involve using rasters and vector data together.

ImageRasterizer	Creates a raster representation of vector or point cloud input features, using the fme_color attribute over a solid background fill for vector features. Point clouds may be rendered using their color or intensity components.
NumericRasterizer	Creates a numeric raster representation of vector or point cloud input features, where cell values are taken from the z coordinates of the input features and overlaid on a uniform background.
MapnikRasterizer	Generates a raster from input vector and raster features, with fine control over symbolization and labeling, using the Mapnik toolkit.
PointCloudOnRasterComponentSetter	Sets point cloud component values by overlaying a point cloud on a raster. The component values for each point are interpolated from band values at the point location.
PointOnRasterValueExtractor	Extracts the band and palette values from a raster at the location of one or more input points and sets them as attributes on the feature.
RasterDEMGenerator	Produces a raster digital elevation model (DEM) by uniformly sampling a Delaunay triangulation generated from input points and breaklines.
VectorOnRasterOverlayer	Rasterizes vector or point cloud features onto an existing raster. For vector features the fme_color attribute sets pixel color, and point clouds may be rendered using their color or intensity components.

Configuration

Input Ports

Output Ports

Parameters

Group Processing

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.

General

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.

Select a method:

Automatic	The transformer will calculate each output point automatically. The Linear method is used if the output point is within a surface triangle in xy and the Nearest Neighbor method is used otherwise.
Linear	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).
Nearest Neighbor	The z value of each output point is set to the z value of the closest vertex in the underlying model.

Output DEM X Cell Spacing
Output DEM Y Cell Spacing

These parameters specify the x and y sampling intervals for the output DEMPoints.

Output DEM Raster Nodata Value

This parameter is used only when Interpolation Method is set to Linear, and it only affects the output port DEMRaster.

All output raster cells that fall outside the underlying surface model’s boundaries will be assigned the value of this parameter.

When this parameter is blank, it is interpreted as NaN (Not a Number).

Note: To ensure consistent raster output, it is highly recommended that you do not leave this parameter blank.

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.

How to Set Parameter Values

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.

Dialog Options - Tables

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.

Reference

Processing Behavior	Group-Based
Feature Holding	Yes
Dependencies	None
Aliases	DEMGridGenerator
History	This transformer was previously named DEMGridGenerator.

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