Define Overviews (Data Management)

Summary

Lets you set how mosaic dataset overviews are generated. The settings made with this tool are used by the Build Overviews tool.

Usage

• This tool is used when there are specific parameters you need to set to generate your overviews, such as

  • Defining the location to write the files
  • Defining an extent that varies from the boundary
  • Defining the properties of the overview images, such as the resampling or compression methods
  • Defining the overview sampling factor
  Otherwise, you can check the option to Update Overviews using the Add Rasters to Mosaic Dataset tool and the defaults will be used.

• Use the Build Overviews tool to generate the overviews after they've been defined with this tool.

• You can use a polygon feature class to define the footprint of the overview. If you do not wish to use all the polygons in the feature class you can make a selection on the layer in the table of contents or use a tool such as Select Layer By Attribute or Select Layer By Location to select the desired polygons.

• The default tile size is 128 by 128. The tile size can be changed in the Environment Settings.

• This tool can take a long time to run if the boundary contains a large number of vertices.

Syntax

arcpy.management.DefineOverviews(in_mosaic_dataset, {overview_image_folder}, {in_template_dataset}, {extent}, {pixel_size}, {number_of_levels}, {tile_rows}, {tile_cols}, {overview_factor}, {force_overview_tiles}, {resampling_method}, {compression_method}, {compression_quality})

Parameter	Explanation	Data Type
in_mosaic_dataset	The mosaic dataset that you want to build overviews on.	Mosaic Layer
overview_image_folder (Optional)	The folder or geodatabase to store the overviews.	Workspace
in_template_dataset (Optional)	A raster dataset or feature class to define the extent of the overviews.	Raster Layer; Feature Layer
extent (Optional)	Set the extent using minimum and maximum x and y coordinates. This is specified as space delimited in the following order: X-minimum X-maximum Y-minimum Y-maximum. The mosaic dataset boundary will determine the extent of the overviews if you do not define an extent.	Envelope
pixel_size (Optional)	If you prefer not to use all the raster's pyramids, specify a base pixel size at which your overviews will be generated. The units for this parameter are the same as the spatial reference of the mosaic dataset.	Double
number_of_levels (Optional)	Specify the number of levels of overviews that you want to generate overviews. A value of -1 will determine an optimal value for you.	Long
tile_rows (Optional)	Set the number of rows (in pixels) for each tile. Larger values will result in fewer, larger individual overviews, and increase the likelihood that you will need to regenerate lower level overviews. A smaller value will result in more, smaller files.	Long
tile_cols (Optional)	Set the number of columns (in pixels) for each tile. Larger values will result in fewer, larger individual overviews, and increase the likelihood that you will need to regenerate lower level overviews. A smaller value will result in more, smaller files.	Long
overview_factor (Optional)	Set a ratio to determine the size of the next overview. For example, if the cell size of the first level is 10, and the overview factor is 3, then the next overview pixel size will be 30.	Long
force_overview_tiles (Optional)	Generate overviews at all levels, or only above existing pyramid levels. NO_FORCE_OVERVIEW_TILES —Create overviews above the raster pyramid levels. This is the default. FORCE_OVERVIEW_TILES — Create overviews at all levels.	Boolean
resampling_method (Optional)	Choose an algorithm for aggregating pixel values in the overviews. NEAREST —The fastest resampling method because it minimizes changes to pixel values. Suitable for discrete data, such as land cover. If the Raster MetadataData Type is thematic, then nearest neighbor will be the default. BILINEAR —Calculates the value of each pixel by averaging (weighted for distance) the values of the surrounding 4 pixels. Suitable for continuous data.This is the default, unless the Raster Metadata Data Type is thematic. CUBIC — Calculates the value of each pixel by fitting a smooth curve based on the surrounding 16 pixels. Produces the smoothest image, but can create values outside of the range found in the source data. Suitable for continuous data.	String
compression_method (Optional)	Define the type of data compression to store the overview images. JPEG —A lossy compression. This is the default, unless the Raster Metadata Data Type is thematic. This compression method is only valid if the mosaic dataset items adhere to JPEG specifications. JPEG_YCbCr —A lossy compression using the luma (Y) and chroma (Cb and Cr) color space components. None —No data compression. LZW —A lossless compression. If the Raster Metadata Data Type is thematic, then nearest neighbor will be the default.	String
compression_quality (Optional)	Choose a value from 1 - 100. Higher values generate better quality outputs, but they create larger files.	Long

Derived Output

Name	Explanation	Data Type
out_mosaic_dataset	The updated mosaic dataset.	Mosaic Layer

Code sample

DefineOverviews example 1 (Python window)

This is a Python sample for DefineOverviews.

import arcpy
arcpy.DefineOverviews_management("c:/workspace/fgdb.gdb/md01", 
                                 "c:/temp", "#", "#", "30", "6", "4000", 
                                 "4000", "2", "CUBIC", "JPEG", "50")

DefineOverviews example 2 (stand-alone script)

This is a Python script sample for DefineOverviews.

#Define Overviews to the default location
#Define Overviews for all levels - ignore the primary Raster pyramid
#Define Overviews compression and resampling method

import arcpy
arcpy.env.workspace = "C:/Workspace"

    
arcpy.DefineOverviews_management("DefineOVR.gdb/md", "#", "#", "#", "#", 
                                 "#", "#", "#", "#", "FORCE_OVERVIEW_TILES",
                                     "BILINEAR", "JPEG", "50")

Environments

Extent, Parallel Processing Factor, Tile Size

Licensing information

• Basic: No
• Standard: Yes
• Advanced: Yes