RasterMosaicker

Merges multiple raster features into a single raster feature.

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Typical Uses

• Merging multiple rasters
• Joining abutting raster tiles together into a single feature
• Merging overlapping raster features together, blending the overlaps
• Preparing data for use in operations that require a single raster feature (eg VectorOnRasterOverlayer)

How does it work?

The RasterMosaicker accepts a number of raster features and combines them into a single raster feature.

The input rasters must all have the same number of bands and palettes, or selected bands and palettes.

Each band is individually mosaicked together, and then appended to the output raster. The output raster will have the same number of bands and palettes as the input (whether whole rasters or selected bands/palettes).

If there are gaps in data (that is, areas not covered by any raster), the empty cells will be filled with nodata values if available, or zero if not.

Bands and Palettes

Rasters may have one band or multiple bands.

Rasters may have no palette, one palette, or multiple palettes. For more information on raster structure, see Rasters (IFMERaster).

Selecting Raster Bands and Palettes

To select specific bands and/or palettes, use the RasterSelector prior to the RasterMosaicker.

• When there are no selected palettes or Merge Palettes is No, each band in a set must have the same band interpretation and nodata value.
• When there are selected palettes and Merge Palettes is Yes, each band must have one selected palette, and all palettes must have the same value interpretation.

A variety of options are available for handling alignment issues, overlapping pixel values, nodata values, and differing resolution.

Attributes from the input features may be merged onto the output raster, and an optional Count attribute will record the number of input features included.

Attributes from the input features may also be appended to an optional list attribute.

Example: Mosaicking adjacent orthophotos

In this example, we start with a set of three individual georeferenced images.

The features are routed into a RasterMosaicker.

The default settings will provide the desired results. We will also add a Count Attribute - Count - to track how many images have gone into the mosaicked image, and create a list attribute called Basenames which will contain the name of each source image.

One single raster feature is output. In the Data Inspector, we can see the new list attribute and count, indicating that three rasters went into the mosaic, and what their names were.

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 combing 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.
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.
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.
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

Input

This transformer accepts only raster features.

Output Ports

Output

One mosaicked raster feature, or one mosaicked raster feature per group if Group By is used.

<Rejected>

Non-raster features will be routed to the <Rejected> port, as well as rasters with elements not compatible with the current mosaicking operation.

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

INVALID_GEOMETRY_TYPE

EXTRA_RASTER_TOO_MANY_PALETTES

INVALID_RASTER_MISMATCHED_NODATA_VALUE

INVALID_RASTER_PALETTE

INVALID_RASTER_BANDS

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.

Parameters

Transformer

Group By

The rasters may be organized into groups with the Group By parameter, with each group of rasters having its own output raster.

Group By Mode

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present. Process 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. Considerations for Using Group By There are two typical reasons for using Process 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 Process At End (Blocking) 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.

Alignment

Snapping Type

Used if the rasters are not perfectly aligned. The first input feature defines the reference grid. Resample: Resamples (if necessary) subsequent raster features to fit the reference grid. Offset: Moves (if necessary) subsequent raster features to fit the reference grid, without resampling. Offsetting may be faster than resampling, but requires that all rasters have the same pixel size.

Interpolation Type

If the input rasters do not line up exactly or if they have different spacings, this transformer will use the selected Interpolation Type to snap and/or resample the input rasters according to the selected method: Nearest Neighbor The simplest and fastest method. Values are copied from the nearest cell. Bilinear Calculates a weighted average, adjusted for distance, from the four (4) nearest cells. Bicubic Calculates a weighted average, adjusted for distance, from the sixteen (16) nearest cells. Average 4 Calculates a simple average from the four (4) nearest cells. Similar to Bilinear and is useful for numeric rasters such as DEMs. Average 16 Calculates a simple average from the sixteen (16) nearest cells. Similar to Bicubic and is useful for numeric rasters such as DEMs.

Data Values

Overlapping Values

Specifies how output cell values will be calculated when rasters overlap. Last The last value. That is, the last raster that overlaps a cell will set the value for that cell. Note that this means the order of the input features may be important. You can use a Sorter transformer to enforce the order in which features are processed. Minimum The minimum value. Maximum The maximum value. Average The average of all values. Sum The sum of all values. Composite Using Alpha Band Values will be blended based on the alpha band. If this option is selected, all input rasters must have exactly one alpha band, and the values from these alpha bands will be used to blend all the other bands' values in areas where overlap occurs, effectively achieving transparency. An alpha value of 0 means complete transparency, and an alpha value of 1 means complete opacity. Note that the Average, Sum, and Composite Using Alpha Band options are not compatible with palettes. When all values for a cell are nodata, the output value will be nodata.

Nodata Overwrites Data

When Overlapping Values is set to Last, this option specifies whether nodata values should overwrite data values in rasters that have been previously drawn. Yes: any nodata overlapping real data values will overwrite the real data values. No: nodata overlapping real data will be ignored, and the real data values will be preserved. Note that data values will always overwrite both nodata and data values.

Palettes

Merge Palettes

Specifies how palettes will be treated when present. Yes: Selected palettes in each input band set will be merged to create a single palette for the output band. No: Selected palettes in each input band set will be accumulated on the output band without modification.

Attributes

Accumulation Mode	Drop Incoming Attributes: Attributes from all incoming features are removed, including the first feature. Merge Incoming Attributes: Attributes from incoming features are merged onto the output raster feature. Use Attributes from One Feature: Attributes from the first input raster feature are retained.
Count Attribute	If a Count Attribute is given, then an attribute with this name will be added to each output feature, containing the number of features that were combined to create the raster feature.

 

Generate List

When enabled, adds a list attribute to the output raster feature, retaining attribute values for each input feature.

List Name	Enter a name for the list attribute. Note: List attributes are not accessible from the output schema in Workbench unless they are first processed using a transformer that operates on them, such as ListExploder or ListConcatenator. Alternatively, AttributeExposer can be used.
Add To List	All Attributes: All attributes will be added to the output raster feature. Selected Attributes: Enables the Selected Attributes parameter, where specific attributes may be chosen to be added.
Selected Attributes	Enabled when Add To List is set to Selected Attributes. Specify the attributes you wish to be added.

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 - whether entered directly in a parameter or constructed using one of the editors.

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.
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.
Working with User Parameters	Create your own editable parameters.

Reference

Related Transformers

RasterConvolver

RasterGeoreferencer

RasterPyramider

RasterResampler

RasterRotationApplier

RasterSelector

RasterSubsetter

RasterTiler

WebMapTiler

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Examples may contain information licensed under the Open Government Licence – Vancouver