RasterCellCoercer

Creates individual points or polygons for each cell in a raster, optionally extracting band values as z coordinates or attributes.

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Typical Uses

Converting a raster to a vector grid of polygons
Converting a raster to regularly spaced points, either 2D or 3D
Creating an elevation grid
Preparing raster data for vector-based analysis

How does it work?

The RasterCellCoercer accepts raster input features. Depending on the choice of Output Cell Geometry - points or polygons - either a point is created at each cell origin, or a polygon is traced around the boundary of each cell.

Band values are extracted from each cell, and may be handled as either Attributes or Z Values.

If values are extracted as Attributes, they are added to a new list attribute on the output features, with one list item per band. If they are extracted as Z Values, they are assigned to the z coordinate of the output features, and they are output as 3D.

Multi-band rasters: If Z Values is used with a multi-band raster, duplicate geometry will be created for each band (which can greatly increase output size and processing time). Extracting values as Z Values is typically most appropriate for single-band numeric rasters or DEMs. If Attributes is chosen on a multi-band raster, the band values (usually representing red, green, blue, and possibly alpha values, in a range from 0 to 255) are added as list items. Color is not assigned to the output features, but may be extracted from this list attribute and assigned using a FeatureColorSetter.

Nodata values may be kept or discarded.

Input raster attributes may optionally be kept, including the Raster ID, Band ID, and source column and row position. As these options may increase processing time, by default they are not added.

This transformer supports raster band selection. The RasterSelector can be used to modify this selection.

When Extract Band Values is set to Z Values, each selected band must not contain a palette.

Examples

Usage Notes

This transformer can easily produce a very large number of vector features for each raster. For example a 1,000 x 1,000 RGBA image, fetched into the Z value, would produce four million point/polygon features. This can lead to the consumption of large amounts of system resources when carrying out transformation on the results, and result in writing very large output datasets.
Very large processing tasks may benefit from using a PointCloudCombiner and PointCloudToPointCoercer as an alternate workflow (for point output only).

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.
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.
RasterSharpener	Enhances the features of a raster image. The RasterSharpener enhances the borders, lines, and curves while reducing noise in the flat areas of the raster image.
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

General

Output Cell Geometry	Points: One point feature will be created for each of the raster's cells, positioned at the cell's origin. Polygons: Polygon features will be output, each one covering one of the raster's cells.
Extract Band Values As	Attributes: One feature will be output per cell in the raster. Band and palette values will be stored in attributes named _band{}.value and _band{}.palette{}.value. The output geometry will be 2D. Z Values: One feature will be output per band per cell in the raster. The output geometry will be 3D, where the z value is the band value.
Extract Nodata Values	Specifies whether point features will be output for Nodata cells in the raster. Yes: A feature will be output for each Nodata cell. No: Features will not be output for Nodata cells in the raster. Note that if No is selected , and all cells in the input raster are Nodata, the feature will be rejected.
Preserve Attributes	Specifies whether output geometry will retain the attributes from the input raster. Note that preserving attributes may add substantial processing time, as they are added to each output feature.

Output Attribute Names

Raster ID	If specified, the name of the new attribute to contain an ID value corresponding to the original raster.
Band ID	If specified, the name of the new attribute to contain an ID value corresponding to the original band. Available when Extract Band Values As is set to Z Values.
Column	If specified, the name of the new attribute to contain the column position of the originating cell. Row 0, Column 0 corresponds to the upper-left corner.
Row	If specified, the name of the new attribute to contain the row position of the originating cell. Row 0, Column 0 corresponds to the upper-left corner.

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	Feature-Based
Feature Holding	No
Dependencies	None
Aliases	GridPointExtractor, RasterPointExtractor, RasterToPointCoercer
History	This transformer was previously known as the RasterToPointCoercer, RasterPointExtractor, or GridPointExtractor.

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