Creating a mosaic dataset containing raster data from multiple dates

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There are many organizations that have large collections of imagery acquired at various dates covering the same area. This data will often be stored in different file formats, in different projections, and with different pixel sizes. For example, forestry companies may have imagery over their forest stands taken at different times of the year or taken over different years to help them manage their harvests. Also, many cities or states have large collections of orthophotography acquired on an annual or semiannual schedule. These collections can be compiled into a single mosaic dataset, which can be used in-house or served as an image service to their clients.

The following workflow assumes you have multiple years of orthophotography that you want compiled into a single mosaic dataset where the user will see the most recent imagery by default. To do this, you will create multiple mosaic datasets—one mosaic dataset for each year—and a final master mosaic dataset. This is the optimal design, because you can maintain each year's orthophotos in a single mosaic dataset collection and easily add new collections to the master without impacting your users.

Caution:

This design is optimal when you have less than eight rows added to your master mosaic dataset.

Create a geodatabase

You will be creating your mosaic datasets in a geodatabase. You can use a single geodatabase or more than one. In this workflow, it is assumed they are all created in a single file geodatabase.

You can right-click a folder in the Catalog window and click New > File Geodatabase or use the Create File GDB tool. You may want to set this geodatabase as the default geodatabase by right-clicking it in the Catalog window and clicking Make Default Geodatabase. This will set the current and scratch workspace location for the geoprocessing environment to this geodatabase.

Create a mosaic dataset for each year

Make sure the raster data is stored on disk in a location where it can be accessed to build the mosaic dataset, and if this is where it will be served, the location also needs to be visible (read access) to the server. Mosaic datasets do not manage the raster data, meaning they do not move or alter the source files. They contain links to the source data.

You will need to create a mosaic dataset for each annual collection of imagery. For example, if your collection can be grouped into six years, such as 1995, 1998, 2000, 2003, 2006, and 2009, you will be creating seven mosaic datasets—one for each of the six years and one master to contain all the years. You will repeat the following steps six times.

1. Create the mosaic dataset (one for each year). You can do this by right-clicking the geodatabase in the Catalog window and clicking New > Mosaic Dataset or opening the Create Mosaic Dataset tool.

   Choose a coordinate system appropriate for the imagery you are adding, if it is not all in the same coordinate system.

2. Add the imagery to each mosaic dataset using the Add Rasters To Mosaic Dataset tool.

   Add the 1995 imagery to the 1995 mosaic dataset, add the 1998 imagery to the 1998 mosaic dataset, and so on.

   1. Check Update Overviews on this tool to build a complete mosaic dataset.
   2. Click Advanced Options and check Build Raster Pyramids and Calculate Statistics.

      These options will build the pyramids and statistics for all the input raster datasets if they don't exist. Alternatively, you can use the Build Pyramids And Statistics tool to compute this information separately.

You should now have six mosaic datasets. It doesn't matter if the boundary or extent of these mosaic datasets are identical, or if the pixel sizes are the same; they can all be combined to create the master mosaic dataset.
You should check each mosaic dataset to be sure it is displaying the imagery correctly.

Create the master mosaic dataset

Next, you will create the mosaic dataset to contain each of the mosaic datasets you created. You could create a reference mosaic dataset, but since you want to add fields and possibly modify the boundary and add additional overviews (from another web service) it's best to create a regular mosaic dataset.

1. Create the master mosaic dataset. You can do this by right-clicking the geodatabase in the Catalog window and clicking New > Mosaic Dataset or opening the Create Mosaic Dataset tool.

   Choose a coordinate system appropriate for all the imagery you are adding, if it is not all in the same coordinate system.

2. Using the Add Rasters to Mosaic Dataset tool, add each mosaic dataset.
   1. Click the Raster Type drop-down arrow and click Raster Dataset.
   2. Click the Input drop-down arrow and click Dataset.
   3. Click the Input browse button and select one of the mosaic datasets.

      Repeat this step until all the mosaic datasets are listed.

   Do not check the option to update overviews, as this workflow will use a web service in place of building overviews for this master mosaic dataset.

3. Click OK.

Add the Year field to the mosaic dataset

To make this mosaic dataset time aware, you need to create the new attribute field in the mosaic dataset and add the correct dates. You can do this using geoprocessing tools or using the steps below within ArcMap.

Add the new field to the footprint attribute table

1. Add the master mosaic dataset to ArcMap.
2. Right-click the Footprint layer and click Open Attribute Table.

   You should see a row for each mosaic dataset you added.

3. Click the Table Options button and click Add Field.
4. Type Year in the Name text box.
5. Click the Type drop-down arrow and click Text.
6. Click OK.

Enter the year values

1. Click the Editor Toolbar button on the Standard toolbar.
2. Click the Editor drop-down menu and click Start Editing.
3. For each row in the table, type the year into the new Year column.
4. Click the Editor drop-down menu, click Stop Editing, then click Yes to save the edits.

Add a service as the overview

By using a service as an overview layer in the mosaic dataset, you can be sure that when your user is zoomed out quite far on the mosaic dataset or image service, they will see a reasonable image. In this set of steps, you will be adding a service from ArcGIS Online and modifying the mosaic dataset's attribute table to set the display settings that will control the scale at which the service and other mosaic datasets display.

1. In ArcMap, click File > ArcGIS Online.

   This opens an ArcGIS Online content browser.

2. Search and identify an image service or cached map service and add it to ArcMap.

   Note:

   You can add several types of web services as source data to a mosaic dataset. Web service-specific raster types include the following:

   • Image Service—Image services from ArcGIS Server
   • Map Service—Cached map services from ArcGIS Server or from ArcGIS Online
   • WCS—Web Coverage Service (OGC standard)
   • WMS—Web Map Service (OGC standard)

   When you add a service from ArcGIS Server, a WCS service, or a WMS service, you can make the connection directly to the server within the Add Rasters To Mosaic Dataset tool or using the Catalog window and add the service to the mosaic dataset, or you can enter the URL. To add a service from ArcGIS Online to the mosaic dataset, you must first save it as a layer file.

3. Right-click the layer you added and save it as a layer file.
4. Right-click the master mosaic dataset in the Catalog window and click Add Rasters.
5. Click the Raster Type drop-down arrow and click the appropriate service type, such as Image Services or Map Service.
6. Click the Input browse button and select the layer file you created.
7. Uncheck Update Boundary.

   You don't want the boundary to update and cover the extent of the entire world. It's best it keep it smaller to cover only your area of interest.

8. Uncheck Update Cell Size Ranges because you want to keep all your current values, and you don't want them modified due to the addition of the service layer.

   You will be manually entering the cell size ranges for the services layer in the following steps.

9. Click OK to run the tool.
10. If the table is closed, right-click the Footprint layer and click Open Attribute Table.

    You should see a new row for the service you added. Next, you need to edit the cell size ranges.

11. Click the gray button at the left side of the newly added row.
12. Right-click the MinPS field and click Field Calculator.
13. Place your cursor in the MinPS text box and type 0.
14. Click OK.

    The minimum pixel size for the service is set to 0. This way, if there is ever an area in your mosaic dataset that doesn't contain data from the other datasets, the area won't appear blank. This is especially useful if you expand or edit your boundary to be larger than the input mosaic datasets.

15. Click the gray button at the left side of the newly added row.
16. Right-click the MaxPS field and click Field Calculator.
17. Place your cursor in the MaxPS text box and type a value that is 10 times greater than the HighPS for the same row.

    For example, if the HighPS is 1564, then enter 15640 for MaxPS.

18. Click OK.
19. Close the attribute table.

You have now created your temporal mosaic dataset.

Examine the temporal mosaic dataset

You can enable time on the mosaic dataset and use the Time Slider window to navigate through the imagery in the mosaic dataset.

1. Zoom in to an area in the mosaic dataset where you can see your high-resolution imagery (not the service imagery).
2. Right-click the mosaic dataset and click Properties.
3. Click the Time tab.
4. Check Enable time on this layer.
5. Click the Time field drop-down arrow and click Year.

   This is the field you created and populated.

6. Click the Time step interval text box and type 1.
7. Click the Time step interval drop-down menu and click Year.
8. Click OK.
9. Click the Open Time Slider Window button on the Tools toolbar.
10. Use the slider to examine the imagery year by year.

Close ArcMap when complete. You can also serve the mosaic dataset as an image service using ArcGIS Server.