Creating a Mosaic Dataset from Orthophotos

Creating a Mosaic Dataset from Orthophotos

On September 10, 2015, Posted by , In ArcMap,NPS Workflow, With Comments Off on Creating a Mosaic Dataset from Orthophotos

Now that you’ve downloaded imagery from the Hurricane SANDY Response Imagery Viewer, you’re ready to start creating a mosaic dataset with the imagery (if you haven’t downloaded imagery yet, please refer to the last blog posting titled “Utilizing NOAA’s Hurricane Sandy Response Imagery Viewer”).

A mosaic dataset is a powerful way to store, manage and utilize large amount of raster data. They also provide the user with additional functionality through the use of functions. For more information on functions, please visit the “Create a Pansharpened Image Using ArcGIS” blog posting from earlier this spring.

To successfully create a high quality mosaic dataset, please follow the instructions below.

First, create new mosaic dataset within a file geodatabase by right clicking on the file geodatabase and selecting New > Mosaic Dataset. This will open the Create Mosaic Dataset tool where you will specify details about the input imagery.

Choose a name for the mosaic dataset, and then specify the appropriate coordinate system; in this case we will specify NAD 1983 UTM Zone 18N, the same as selected for the Hurricane SANDY Response Imagery we downloaded in the previous blog post. Next, it is important to specify pixel properties; these properties vary with imagery, so it is important to check the number of bands and pixel type each time you work with new imagery. To do this, bring one tile into ArcMap, right click on it in the Table of Contents and select properties. Navigate to the Source tab and determine the number of bands (3), and the pixel type (16 Bit, Unsigned).

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

  1. Raster type = Raster dataset
  2. Input Data = Dataset
    • Then click the folder icon and add all tiles (red circle below).
  3. Check: Update boundary, Update overviews (this automatically checks Update Cell Size)
  4. Under Advanced Options:
    • Coordinate System = select same Coordinate system as previously (in this case NAD 1983 UTM Zone 18N)
    • Add New Datasets Only = Allow Duplicates
    • Check: Build raster pyramids, Calculate statistics
  5. Click OK to run the tool.

Next, it will be necessary to build footprints. Right click the mosaic dataset, choose Modify > Build Footprints. This will calculate the footprint for each input raster in the mosaic dataset. 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 edges, skip overviews, update boundary
  6. Simplification Method = None
  7. Request Size = -1
  8. Minimum Region Size = 100
  9. Leave everything else as default and click OK to run the tool.

Now you’re ready to build seamlines. These help to ensure that the resulting mosaicked image is the best possible mosaic because it will prevent the line between images from being obvious. To do this, right click the mosaic dataset and choose Enhance > Generate Seamlines. Once the tool is open:

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

Now, right click on mosaic dataset in ArcCatalog > Properties > Default Tab.

  1. Set Allow Mosaic Methods to seamline by unchecking everything else. Also leave seamline as the default method.

  1. Set “Default Mosaic Operator” to Blend.
  2. Click Apply, then OK.

The final step is to build overviews. To do this, right click on the mosaic dataset and select Optimize > Build Overviews; leave all of the tool settings as the default, and click OK to run tool.

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 park of a larger document available for download on the IRMA Portal.

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