Changing the mosaic method used when viewing the mosaic dataset

The mosaicked image displayed from a mosaic dataset can be created from a number of input rasters. The mosaic method defines how the mosaicked image is created from these rasters. For example, when using the By Attribute method, the values in an attribute field are used to sort the images, and when using Closest to Center, the image closest to the center of the display is positioned as the top image in the mosaic. Additionally, the mosaic operator allows you to define how to resolve the overlapping cells, such as choosing a blending operation.

When working with the mosaic dataset, there are two places to modify the mosaic method. If you're editing the mosaic dataset and you need to set the mosaic method, you can modify the mosaic dataset properties. This permanently alters the mosaic dataset. However, if you're viewing the mosaic dataset as a data source and not modifying it for the benefit of others, you can change the mosaic method from the Image layer. This way, you only impact your display and do not permanently impact others when viewing or accessing the mosaic dataset.

The mosaic methods are defined as part of the mosaic dataset properties, but all may not be available. The mosaic methods include the following:

• Closest to Center—Enables rasters to be sorted based on a default order where rasters that have their centers closest to the view center are placed on top.

  In this example, 12 rasters are displayed using the Closest to Center mosaic method. You can see that the center raster (pink) is completely displayed and the remainder of the mosaicked image is composed of the remaining rasters. As you pan and zoom around the mosaicked image, it will change as other rasters become closest to the center within the display extents.

• Closest to Nadir—Enables rasters to be sorted by the distance between the nadir position and view center. This is similar to the Closest to Center method but uses the nadir point to a raster, which may be different than the center, especially for oblique imagery.

• Closest to Viewpoint—Orders rasters based on a user-defined location and nadir location for the rasters using the Viewpoint tool.

  In this example, imagine zooming in to the area located at the tip of the red arrowhead. This location comprises six overlapping rasters. Using the Viewpoint tool, you will get those rasters displayed under the blue arrows, which represent the viewpoint selection.

• By Attribute—Enables raster ordering based on a defined metadata attribute and its difference from a base value.

  In this example, the chosen attribute field contains letters of the alphabet, and it's sorted in an ascending order.

• North-West—Enables raster ordering in a view-independent way, where rasters with their centers to the northwest are displayed on top.

  In this example, the raster in the northwest corner is used completely to create the mosaicked image.

• Seamline—Cuts the raster using the predefined seamline shape for each raster using optional feathering along the seams and orders images based on the SOrder field in the attribute table.

  In this example, the seamline (blue) is used to create the mosaic method and the sort field is the same as the By Attribute example above.

• Lock Raster—Enables a user to lock the display of single or multiple rasters based on the ObjectID.

  In this example, four footprints are selected; therefore, the mosaicked image is created from only four rasters.

• None—Orders rasters based on the order (ObjectID) in the mosaic dataset attribute table.

  In this example, the mosaicked image is generated based on the order of the rasters in the attribute table.

When using a date field with the By Attribute mosaic method, the base value must be entered using one of the following:

• yyyy/MM/dd HH:mm:ss.s
• yyyy/MM/dd HH:mm:ss
• yyyy/MM/dd HH:mm
• yyyy/MM/dd HH
• yyyy/MM/dd
• yyyy/MM
• yyyy

To use the Closest to Viewpoint mosaic method, you need to add the Viewpoint controller to your application. To do this, see Using the Viewpoint window.

The mosaic operators include the following:

• First—The overlapping areas will contain the cells from the first raster dataset listed in the source.
• Last—The overlapping areas will contain the cells from the last raster dataset listed in the source.
• Min—The overlapping areas will contain the minimum cell values from all the overlapping cells.
• Max—The overlapping areas will contain the maximum cell values from all the overlapping cells.
• Mean—The overlapping areas will contain the mean cell values from all the overlapping cells.
• Blend—The overlapping areas will be a blend of the cell values that overlap; this blend value relies on an algorithm that is weight based and dependent on the distance from the cells to the edge within the overlapping area.

Generally, the mosaicked image is created using the following process:

1. A spatial query defines the potential images.
2. The current scale is compared with the minimum and maximum pixel values of the potential images.
3. The qualified images are selected and sorted according to the mosaic method (the sorting order can be ascending or descending).
4. The overlapping area is resolved by the mosaic operator.

When the Lock Raster mosaic method is specified, the first two steps above are not used.

Steps:

1. In ArcMap, expand the mosaic dataset layer in the table of contents, right-click the Image layer, then click Properties.

   In ArcGlobe, right-click the mosaic dataset layer and click Properties.

2. Click the Mosaic tab.
3. Click the Mosaic Method drop-down arrow and choose a method.
   • If you choose By Attribute, you can specify a field and base value.
   • If you choose Lock Raster, you can specify a raster ID value to which the mosaic dataset will be locked.
4. Optionally, uncheck Sort Ascending.

   This reverses the ordering method.

5. Optionally, click the Mosaic Ordering drop-down arrow and choose a different ordering method.