Raster Reclassification

Input Layer – Specify the layer to perform the reclassification on. The left side of the dialog will change depending on the type of input layer. Palette data will show the Reference Palette table. Continuous data including elevation and imagery will show a histogram of the input file.

Reclassified Layer Name – Specify the name of the resulting layer. By default, this will be the input layer with -Reclassified appended.

Layer Type- The output raster layer can be stored as a palette image, or a single band raster layer. Choose between the palette, 8-bit single band and 16-bit single band options. A palette image has colors associated with index values, and also optionally can contain class descriptions. Single band images are simple rasters with just integer values. They can be used with any terrain analysis tools (contouring, slope calculation, etc.).

NO DATA Color - Use this to define a single NO DATA color; this ensures users do not accidentally use that color in any color change (not NO DATA) rules. Default value is initialized from the selected input layer; will use layer's transparent color, if configured, or first entry in palette (commonly reserved for NO DATA in GIS imagery). Color and index in loaded gmr file will be overwritten if not compatible with currently selected layer. The user can still pick a color when adding/editing a NO DATA rule, but the color will be replaced with the configured NO DATA color on validation.

Set Unlisted Values to No Data Value - Check this option to ignore any values in the input layer that are not listed in the output reclassification rules. Unlisted values will be set as 'No Data' pixels when this option is checked. If unchecked, the input values that are not listed in an output rule will stay as the same values.

Reclassify Within Selected Area Features - Check this option to crop the generated reclassified layer to the selected area feature(s) in the workspace. Select the area features before opening the reclassification tool. This option is disabled if no area features are selected.

Reference Palette

The reference palette table on the left side of the dialog shows information about the input layer if the input is a palette image. This table is optional and does not need to be used, but can provide a helpful reference for specifying the input and output values in the Raster Reclassification Rules specified on the right table. Use the Load Palette from Layer button to populate the left table with the values present in the input image.

When the left table is populated, one or more rows from the input palette can then be selected and dragged to the populate the Reclass Rules table on the right side. Two options are available for copying values from the left reference palette into the right Raster Reclassification Rules table:

1. Combine many values into a single output - drag left to right: Use the Shift or CTRL keys to highlight multiple rows in the reference palette. Drag the highlighted rows to the right reclassification table to combine them into a single Output Index value. The default color will be an average of the combined inputs when copying to a blank row.

   Example: The first option is to copy a range of rows from the Input Layer to a single output row in the Reclass Rules. This option is useful to reclassify multiple pixels to a single value. For example, one might want to reclassify all Tree Cover pixels (values 50, 60, 61, 62, 70, 71, 72, 80, 81, 82) to a single pixel value of Trees with a value of 50. Select all the input rows from the reference palette and drag them onto the Reclass Rules. Enter an optional Description in the newly created row. Note that the color of the new row is an average of the colors from the reference palette. If this is not acceptable, you can change the color by clicking on it and choose from the Color Picker dialog.

   

2. Keep unique values- CTRL and drag left to right: Use the Shift or CTRL keys to highlight multiple rows in the reference palette. Drag the highlighted rows to right reclassification table while holding down the CTRL key to move each input layer into the output. By default this rows will maintain the same input Palette Index and Output Index, as well as description and Color.

   Example: The second option is to copy the selected rows from the reference palette into separate rows in the raster reclass rules. To perform a copy, hold the Ctrl key while dragging to rows. See example below.

   

Load Palette From Layer– Reads the palette information from the layer and populates the left hand palette list

Load Palette From File – Reads the palette information from a palette file and populates the left hand palette list

Histogram

If the input layer is a continuous raster, such as imagery or terrain data, the left side of the dialog will display a histogram of the layer for reference. Use the Number of Bins value to change the number of histogram bars, then press Refresh Graph to update.

With multi-band imagery data, there is a dropdown to select the raster band. Raster Reclassification can only be performed on one band of data at a time. Choose the band which will be reclassified into a single band layer.

For more info on the histogram options, see Histogram Tab.

Raster Reclassification Rules

The table on the right side of the dialog will be populated with the raster reclassification rules. This table specifies the new output pixel value for each input pixel value or set of input pixel values. This table can be populated by dragging rows from the left table, by right clicking and manually entering new rows, or by using the load button to populate the Raster Reclassification Rules with an existing palette or previously saved Raster Reclassification Definition.

• Palette Indices – Specify the input pixel values that will be converted to the output. This can be listed as a single value, comma separated values, or a range of values using a - . It is also acceptable to add a row containing the keywords else, other or default (case insensitive) to capture all input pixel values not specified in another row.

• Output Index – Specify the output Palette Index to be applied when reclassifying the input Palette Indices. If the output index is set to 0, cells with this value will be set to NODATA in the output raster.

• Description - Optionally specially a palette description.

• Color - Specify a color for the palette value in the output image. Click the color to bring up the Color picker dialog, which also includes a choice to Pick Color from Map.

  

The reclass rules can be edited manually to create reclassification rules. Double click on a Reclass Rule cell to edit it. Use the Return key to complete editing, or the tab and arrow keys to move to different cells.

In addition, right-clicking the mouse in the Reclass Rules grid will bring up a menu option to add or delete a row. The Insert Row option in the context menu will add a new blank row to the reclass rules grid. Delete Rows will delete all highlighted rows.

Create Spread

It is also possible to automatically create rows in the reclassification rules at a repeating interval. The input values will repeat a range at the next interval, while the output values increment up by a specified step size.

Reclass Rule Conditions

With reclassification rules it is possible to reference a range or values, set a value for all remaining inputs, and also set some outputs to a null 'no data' value. When editing the reclass rules, the following conditions must be followed.

Saving, Loading and Validating

Load – This loads in the palette or saved Raster Reclassification Definition file specified in the drop-down to the right and populates the Raster Reclassification Rules table below.

Save – Saves the Raster Reclassification Rules specified in the table to a Raster Reclassification Definition file that can be reused for future reclassifications. This is a *.gmr file that is a comma separated list of the values specified in the table that list the input Palette Indices, Output Index, Description and RGB Color value.

Validate – Checks the Raster Reclassification Rules and combines values into ranges where appropriate. To ensure the rules are correct, press the Validate button. This will check that all the conditions in the above table are met, and group individual Palette Indices together for equal Output Index values. Validating will not only check the data, but also sort it by Output Index.