Merges multiple raster features into a single raster feature.
- 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.
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.
Working with Rasters
|RasterCellOriginSetter||Sets the raster's cell origin.|
Accepts input features containing a raster geometry and outputs the features after applying a convolution filter to all the bands.
Convolution filters are applied using a kernel, specified by a matrix of weights for the neighboring values, over all the cells of an input raster geometry. Such filtering is used for smoothing, sharpening, enhancing edges and other raster image manipulation operations.
|RasterExpressionEvaluator||Evaluates expressions on each cell in a raster, such as algebraic operations or conditional statements.|
|RasterExtentsCoercer||Replaces the geometry of input raster features with a polygon covering the extents of the raster.|
|RasterGCPExtractor||Extracts the coordinate system and the Ground Control Points (GCP) from the raster feature and exposes them as attributes.|
|RasterGCPSetter||Sets the Ground Control Points (GCP) on a raster with the specified Column (pixel), Row (line), X Coordinate, Y Coordinate and Z Coordinate.|
|RasterGeoreferencer||Georeferences a raster using the specified parameters.|
|RasterHillshader||Generates a shaded relief effect, useful for visualizing terrain.|
Alters the underlying interpretation of the bands of the raster geometry on the input features, using the specified conversion options.
For example, an input raster feature with three bands of interpretation (UInt16, Gray8, and Real64) could be converted to a raster feature with three bands of interpretation (Red8, Green8, and Blue8) or four bands of interpretation (Red16, Green16, Blue16, and Alpha16) in a single operation.
|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||Creates a series of pyramid levels for each input raster feature by specifying either the smallest pyramid level size or the number of pyramid levels to generate. Pyramid levels are created by resampling input rasters to various different resolutions.|
|RasterResampler||Resamples an input raster using the desired dimensions, the desired cell size in ground units, or a percentage of the size.|
Applies the raster rotation angle on the input raster properties to the rest of the raster properties and data values.
The expected input is a raster with a non-zero rotation angle and the expected output is a rotated raster with a rotation angle of 0.0. It is expected that the input raster properties will be modified to conform the output raster properties for a raster rotated by the given angle.
Applying a rotation angle is primarily done for compatibility with other processing and writers that cannot handle a rotation angle.
|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
|RasterBandAdder||Adds a new band to a raster. The added band will have the same value in all cells, and the same raster-level properties as other bands in the raster (that is, number of rows/columns, cell spacing, cell origin, and so on).|
|RasterBandCombiner||Merges multiple overlapping raster features into a single raster feature. It accepts a number of input raster features, each of which has one or more bands. The bands are removed from the input features and appended to a single output raster feature.|
Alters the underlying interpretation of the selected bands of the raster geometry on the input features, using the specified conversion options.
For example, an input raster feature with a single band of interpretation UInt8 could be converted to a single band of Gray8 or UInt16 data.
Removes all bands of a raster, except for those that are selected. The RasterSelector can be used to modify the selection.
If all bands in the source raster are selected, the raster will remain unchanged.
|RasterBandMinMaxExtractor||Extracts the band minimum and maximum values, palette minimum and maximum keys and palette minimum and maximum values of a raster feature and exposes them as attributes.|
|RasterBandNameSetter||Sets the name of selected bands on a raster.|
|RasterBandNodataRemover||Removes the existing nodata identifier from the selected bands of a raster feature. That is, any values that were previously equal to the nodata value will now be considered valid data.|
|RasterBandNodataSetter||Identifies a value to act as a nodata identifier on a raster feature at the band level. That is, values equal to the specified value will now be considered invalid, and will not be affected by many operations (for example, offsetting or scaling).|
|RasterBandOrderer||Specifies the 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 the selected band(s) of a raster. To modify the selection, see the RasterSelector.|
|RasterBandSeparator||Separates the bands and palettes from each input raster feature into one or more output raster features based on the number of input bands and palettes.|
|RasterStatisticsCalculator||Calculates statistics on raster bands and exposes them as attributes. Bands with palettes are valid.|
Working with Cells
Calculates the aspect (direction of slope) for each cell of a raster. Aspect is measured in degrees from 0 to 360, starting clockwise from the north.
Each selected input band will be converted to a Real64 band with output values that represent the aspect. If an input band does not have a nodata value, the output band nodata value will be set to -1.
|RasterCellCoercer||Decomposes all input numeric raster features into individual points or polygons. One vector feature is output for each cell in the band.|
|RasterCellValueCalculator||Performs an arithmetic operation on a pair of rasters.|
|RasterCellValueReplacer||Replaces a range of values in the source raster with a new single value.|
|RasterCellValueRounder||Rounds off raster cell values.|
|RasterSingularCellValueCalculator||Performs an arithmetic operation on two operands: the cell values of a raster and a numeric value.|
|RasterSlopeCalculator||Calculates the slope (maximum rate of change in z) for each cell of a raster.|
Working with Palettes
Creates a palette from an attribute, and adds this palette to all selected bands on a raster.
Selected bands are required to have an interpretation of UINT8, UINT16, or UINT32. Note that palette entries will be discarded if they do not fit within the interpretation of a selected band. For example, when adding a palette to a UINT8 band, all keys that are greater than 255 will be dropped.
|RasterPaletteExtractor||Creates a string representation of an existing palette 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.|
Alters the underlying interpretation of the palettes of the raster geometry on the input features, using the specified conversion options.
For example, an input raster feature with a single band with a single palette of interpretation RGB24 could be converted to a single band with a single palette of RGB64 or String data.
Identifies the nodata value on a raster feature at the palette level.
The transformer will succeed in setting the specified nodata value only if the input raster band(s) have at least one palette and a nodata key has already been set on the band.
|RasterPaletteRemover||Removes the selected palette(s) of a raster. The palette's band retains the palette key, but the corresponding values are lost.|
|RasterPaletteResolver||Resolves the palettes of the selected bands of the input raster features by using the band cell values to look up the corresponding palette values, which then replace the original band cell values in the raster.|
|RasterCheckpointer||Sets a checkpoint in the raster processing which forces previous processing to occur immediately. Once complete, it saves the current state to disk.|
|RasterConsumer||Requests the tile(s) from the raster geometry but no actual operations are performed on the tile(s).|
|RasterExtractor||Serializes the geometry of the feature into the Blob Attribute based on the selected writer format.|
|RasterNumericCreator||Creates a feature with a raster of the specified size with a numeric value and sends it into the workspace for processing. It is useful for creating a very large image with a user-specified width and height.|
|RasterReplacer||Replaces the geometry of the feature with the geometry held in the Blob Attribute. The blob is decoded according to the selected raster format.|
|RasterRGBCreator||Creates a feature with a raster of the specified size with an RGB value and sends it into the workspace for processing.|
Selects specific bands and palettes of a raster for subsequent transformer operations.
The bands and palettes are selected using the band and palette indices, specified in a string. The string may either be specified explicitly or through an attribute. The format of the string is B P (separated with a space), where B is the band index and P is the palette index of the band and palette to be operated on. Indices are zero-based, so the first band or palette is at index 0.
Vectors and Rasters
|ImageRasterizer||Draws input point, line and polygon features onto a color raster filled with the background color. The fme_color attribute of the input vector features is used to generate pixel values. Features without an fme_color attribute will be discarded.|
|NumericRasterizer||Draws input point, line and polygon features onto a numeric raster filled with the background value. The Z coordinates of the input vector features are used to generate pixel values. Features without Z coordinates will be discarded.|
|MapnikRasterizer||Draws input point, line, polygon, and raster features onto a raster using the Mapnik toolkit.|
|PointOnRasterValueExtractor||Extracts the band and palette values from a raster at the location of each input point and sets them as attributes on the feature.|
|VectorOnRasterOverlayer||Overlays vector features onto a single raster feature by drawing them onto the resulting output raster. The properties of the output raster are identical to that of the input raster.|
This transformer accepts only raster features.
One mosaicked raster feature, or one mosaicked raster feature per group if Group By is used.
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:
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.
|Group By||The rasters may be organized into groups with the Group By parameter, with each group of rasters having its own output raster.|
Select a level of parallel processing to apply. Default is No Parallelism.
Note: How parallel processing works with FME: see About Parallel Processing for detailed information.
This parameter determines whether or not the transformer should perform the work across parallel processes. If it is enabled, a process will be launched for each group specified by the Group By parameter.
Parallel Processing Levels
For example, on a quad-core machine, minimal parallelism will result in two simultaneous FME processes. Extreme parallelism on an 8-core machine would result in 16 simultaneous processes.
You can experiment with this feature and view the information in the Windows Task Manager and the Workbench Log window.
No: This is the default behavior. Processing will only occur in this transformer once all input is present.
By Group: This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger batch processing on the currently accumulating group. This will improve overall speed if groups are large/complex, but could cause undesired behavior if input groups are not truly ordered. Specifically, on a two input-port transformer, "in order" means that an entire group must reach both ports before the next group reaches either port, for the transformer to work as expected. This may take careful consideration in a workspace, and should not be confused with both port's input streams being ordered individually, but not synchronously.
Considerations for Using Input is Ordered By
Using Ordered input can provide performance gains in some scenarios, however, it is not always preferable, or even possible. Consider the following when using it, with both one- and two-input transformers.
Single Datasets/Feature Types: Are generally the optimal candidates for Ordered processing. If you know that the dataset is correctly ordered by the Group By attribute, using Input is Ordered By can improve performance, depending on the size and complexity of the data.
If the input is coming from a database, using ORDER BY in a SQL statement to have the database pre-order the data can be an extremely effective way to improve performance. Consider using a Database Readers with a SQL statement, or the SQLCreator transformer.
Multiple Datasets/Feature Types: 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, using Ordering with multiple feature types is more complicated than processing a single feature type.
Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.
One approach is to send all features through a Sorter, sorting on the expected Group By attribute. The Sorter is a feature-holding transformer, collecting all input features, performing the sort, and then releasing them all. They can then be sent through an appropriate filter (TestFilter, AttributeFilter, GeometryFilter, or others), which are not feature-holding, and will release the features one at a time to the transformer using Input is Ordered By, now in the expected order.
The processing overhead of sorting and filtering may negate the performance gains you will get from using Input is Ordered By. In this case, using Group By without using Input is Ordered By may be the equivalent and simpler approach.
In all cases when using Input is Ordered By, if you are not sure that the incoming features are properly ordered, they should be sorted (if a single feature type), or sorted and then filtered (for more than one feature or geometry type).
As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.
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.
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:
Specifies how output cell values will be calculated when rasters overlap.
|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.
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.
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.|
When enabled, adds a list attribute to the output raster feature, retaining attribute values for each input feature.
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. All list attribute transformers are displayed in the Contents pane of the Transformer Help under Lists. 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.
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.
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.
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.
Set values depending on one or more test conditions that either pass or fail.
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.
|These functions manipulate and format strings.|
|A set of control characters is available in the Text Editor.|
|Math functions are available in both editors.|
|These operators are available in the Arithmetic Editor.|
|These return primarily feature-specific values.|
|FME and workspace-specific parameters may be used.|
|Working with User Parameters||Create your own editable parameters.|
|FME Licensing Level||FME Professional Edition and above|
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Examples may contain information licensed under the Open Government Licence – Vancouver