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Part 1: Creating a Panchromatic Mosaic Dataset

Part 1: Creating a Panchromatic Mosaic Dataset

Quickbird is a high-resolution commercially-owned (DigitalGlobe) “earth-orbiting” satellite that is used to collect high-accuracy imagery; this imagery is available in both panchromatic (black and white) and multispectral (a wide range of frequencies across the electromagnetic spectrum). While the data used in this example is unavailable for testing, some sample Quickbird imagery can be downloaded from the FTP site at the Global Land Cover Facility by University of Maryland, College Park.

To work with this imagery we will be utilizing a mosaic dataset. This powerful way to store and manage raster data is extremely effective as it provides the user with added functionality to enhance the imagery and produce a polished, high quality final product.

First, create new mosaic dataset within a file geodatabase by right clicking on the file geodatabase in ArcCatalog, select New > Mosaic Dataset in the context menu. This will open the Create Mosaic Dataset tool where details about the input imagery will be specified. The first step is to name the mosaic dataset; the best practice for this would be to select a name that specifies the collection area, type of data and the date of collection (ie. GatewayNRA_Quickbird_2012). Next, use the following directions to complete the remainder of the tool:

  1. Coordinate System = Choose based on Area of Interest (NAD 1983 UTM Zone 18N  was used for this example based on the area of interest - Gateway National Recreation Area)
  2. Product Definition = None
  3. Pixel Properties:
    • Number of Bands = 1
    • Pixel Type = 16 bit unsigned (use the down arrow to select)
  4. Click OK to run the tool.

To add rasters to the mosaic dataset, right click on the mosaic dataset in ArcCatalog, and choose Add Rasters from the context menu. Within this tool fill in the following specifications:

  1. Raster type = Raster Dataset
  2. Input Data = Dataset
    • Click the folder icon (red circle below) and add the correct imagery from the files ending in _PAN (the rasters need to have the TIFF extension[.tif]).
  3. Check:  Update Cell Size Ranges and Update boundary.
  4. Under Advanced Options:
    • Coordinate System = select same Coordinate system as previously.
  5. Click OK to finish adding the images to the mosaic dataset.

Next we need to Build Footprints. Footprints are calculated based on each raster image that was input into the mosaic dataset. Footprints help to determine which data is displayed in the mosaicked image. To do this, right click on the Mosaic dataset again, and choose Modify > Build Footprints; once the tool is open:

  1. Computation Method = Radiometry
  2. Minimum data Value = 1
  3. Maximum data Value = Default value (this changes based on input imagery)
  4. Approximate Number of Vertices = 30
  5. Check: Maintain sheet edges, skip overviews, update boundary.
  6. Simplification Method = None
  7. Within Advanced Options set the Request Size = -1
  8. Minimum Region Size = 100
  9. Click OK to run the tool.

Now you’re ready to build seamlines. These help to ensure that the mosaicked image will appear to the highest quality, as they define the lines along which the images are “stitched” together. To do this, right click on the mosaic dataset and choose Enhance > Generate Seamlines. Once open, fill in the following options:

  1. Computation Method = Radiometry
  2. Sort Method = North_West
  3. Leave everything else as default
  4. Click OK to run the tool.

 

Now it is necessary to right click on mosaic dataset in ArcCatalog and select Properties from the context menu. Navigate to the Defaults Tab.

  1. Within the Image Properties section, set Allowed Mosaic Methods to seamline by unchecking everything else. Also leave seamline as the default method.
    • To do this, click on the  button.
  2. Set “Default Mosaic Operator” to Blend by clicking the down arrow.
  3. Click Apply, then OK.

Now it is time to calculate statistics for the mosaic dataset. It will be necessary to do this for each input raster, as well as the mosaic dataset. Without doing this for each raster, it will not be possible to color balance the mosaic dataset.

Use the Build Item Pyramids and Statistics tool to do this. This can be found by right clicking the mosaic dataset and selecting Modify > Built Item Pyramids and Statistics. Within the tool fill out the following options:

  1. Leave all default values in the first section.
  2. Expand the Statistics Options section
    1. Check the box for Include Source Datasets.
  3. Click OK to run the tool.

If for some reason statistics are NOT calculated with this method, please use the following work-around. This will “estimate” statistics, however the estimated values are the same as the values calculated using the “Calculate Statistics” tool.

  1. Open the Image Properties dialog box for your mosaic dataset by double clicking the Image in the Table of Contents.
  2. Navigate to the Symbology tab.
    1. Change the Stretch Type to Percent Clip.
    2. Click YES on the warning that appears.
    3. Click Apply and then OK to save changes.
    4. Refresh the Mosaic Dataset in your Table of Contents.
      • Right click and select Refresh.

Next, it is necessary to build overviews. Do this by right clicking the mosaic dataset and selecting Optimize > Build Overviews. Click OK to run the tool with default values. This will result in a complete mosaic; it should be fairly dark.

We have not built overviews before now, as they need to be constantly updated with each change such as building footprints, generating seamlines, etc. It will be necessary to re-run this tool to see any changes made after color balancing.

Next, right click on the mosaic and choose enhance > Color Balance.

NOTE: This step of the process may require multiple runs of this tool to get the proper color balance; these inputs worked for this dataset, but requirements may be different based on the imagery. It will also be necessary build overviews every time this process is repeated (re-run the steps for color balancing and building overviews each time).

  1. Balance Method = Standard Deviation
  2. Under Pre-processing Options, select a self-created* file for the Exclude Area Raster.
    • In this case it was necessary to cover the Jamaica Bay Water Area as the black pixel values of the water will distort the coloring of the rest of the image. This may not be necessary based on the area of interest if a large amount of water area is not present this step may be irrelevant.
  3. Click OK to run the tool.

* This Exclude Area Raster is a SELF CREATED raster that covers the water area of Jamaica Bay.

Please note that it may be necessary to explore other input options if this does not work (such as selecting a target raster, or selecting pre-processing). For example, it may be necessary to try the Build Pyramids and Statistics tool (Data Management) if the above steps prove unsuccessful.

 

Finally, right Click on the mosaic dataset and choose Optimize > Build Overviews. Leave all values as default and click OK to run.

Note: If the above procedure for color balancing the mosaic dataset does not work, please try re-running the tool. As mentioned previously, these steps worked for this particular dataset, but many not be appropriate for all datasets. After each trial, it will be necessary to re-build overviews.

 

This blog posting was developed with the support of a competitive grant (cooperative agreement number P09AC00212; task agreement number P13AC00875) from the National Park Service in partnership with the North Atlantic Coast Cooperative Ecosystems Studies Unit. It is part of a larger document available for download on the IRMA Portal.​

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Authored by

erica
 

Last updated

09/10/2015 - 08:41