Calculates the slope (maximum rate of change in z) for each cell of a raster.

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Typical Uses

  • Calculating slope on elevation rasters
  • Calculating the rate of change on raster band values

How does it work?

The RasterSlopeCalculator receives raster features, and calculates the slope for each cell.

Slope may be measured in either Degrees (0 to 90), or Percent Rise (0 to infinity). The calculation is done based on the values of surrounding cells (using a 3 cell x 3 cell window), and a choice of algorithms is available. Cells without data (Nodata) may be interpolated for calculation purposes.

Slope values are output on the same band they were calculated from, and the band is converted to Real64.

For multi-band rasters, each band is processed separately, with slope values calculated for each band on each cell. To restrict operation to specific band(s), use a RasterSelector prior to the RasterSlopeCalculator.

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

Z Factor, Scaling and Units

Input rasters’ horizontal (x and y) units are expected to be the same as vertical (z) units.

If this is not the case - for example, if the horizontal units are in meters with elevation (z) in feet (or any other similar unit type mismatch), you may apply a scale factor (also known as Z Factor) with the Scaler transformer prior to using a RasterSlopeCalculator.

In this example (ground units are meters, elevations are feet), the scale factor to use is 0.3048 - the number of meters in one foot.

If the ground units are lat/long, the appropriate scale factor will vary greatly between the equator and the poles. In this case, consider reprojecting the input raster with a Reprojector, to an appropriate coordinate system with ground units matching the vertical (z) units.


Usage Notes

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).


Input Ports

Output Ports


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.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.


Processing Behavior


Feature Holding


Dependencies None

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