Exercise 4: Creating a mosaic dataset using a raster type for orthorectification

This topic applies to ArcGIS for Desktop Standard and ArcGIS for Desktop Advanced only.

Complexity: Beginner Data Requirement: ArcGIS Tutorial Data for Desktop Data Path: C:\arcgis\ArcTutor\Raster\Data Goal: To create a mosaic dataset using the MATCH-AT raster type, which will create on-the-fly orthorectified mosaicked images

In this exercise, you will create a mosaic dataset using raw aerial imagery, a DEM, and some parameter files. The imagery added to this mosaic dataset has been processed with MATCH-AT and will be added to the mosaic dataset using the MATCH-AT raster type.

Since there are so many overlapping images, you may find it useful to create seamlines to define how the images will be mosaicked, which this tutorial will also demonstrate.

This exercise does not rely on any previous exercises.

Before you begin, it is assumed that you have installed the tutorial on the C:\ drive. If not, you will need to edit the hard-coded paths to the data in the MATCH-AT project file (Amberg_MAT2.prj in \arcgis\ArcTutor\Raster\Data\Amberg_scans\Match-AT Parameters). This project file is a text file you can open in any text editor program (such as Notepad or WordPad). Search for the string C:\ImageServerTutorial\Data\Amberg_scans\Scans and replace it with your path to the \Scans folder containing the .tif files. This path appears 16 times in this file.

For example, if your path to the tutorial data begins with D:\mydata, you will likely replace text in the line:

$PHOTO_FILE: C:\arcgis\ArcTutor\Raster\Data\Amberg_scans\Scans\110211.tif

with

$PHOTO_FILE: D:\mydata\arcgis\ArcTutor\Raster\Data\Amberg_scans\Scans\110211.tif

Start ArcMap

Steps:

1. Start ArcMap by clicking Start > All Programs > ArcGIS > ArcMap 10.1.
2. Click Cancel on the ArcMap - Getting Started window.

   This window may not open if you've previously opted not to show it.

   Note:

   You will be setting the default map document's geodatabase later in this exercise.

Create a file geodatabase

If you have already created the ImageGDB in another exercise, you can skip this section of steps.

Steps:

1. Click the Catalog button on the Standard toolbar.

   This opens the Catalog window.

2. In the Location text box, type C:\arcgis\ArcTutor\Raster and press ENTER.

   This location is added to the Catalog tree under the Folders Connection heading.

   If your tutorial data was installed in a different location, alter the path according to your installation location.

3. Right-click the Raster folder and click New > Folder.
4. Name the folder Exercises.
5. Right-click the Exercises folder and click New > File Geodatabase.
6. Rename the new file geodatabase ImageGDB.

Set the default geodatabase

Each map document has a default geodatabase, which is the home location for the spatial content of your map. This location is used for adding datasets and saving resulting datasets created by various editing and geoprocessing operations.

Learn about the default geodatabase

Steps:

1. Right-click the ImageGDB geodatabase in the Catalog window and click Make Default Geodatabase.

Create a new mosaic dataset

Steps:

1. Right-click the ImageGDB in the Catalog window and click New > Mosaic Dataset.

   This opens the Create Mosaic Dataset tool.

2. Type AmbergOrtho in the Mosaic Dataset Name text box.
3. Click the Coordinate System browse button .
4. Expand Projected Coordinate Systems > National Grids > Germany, select Germany Zone 4.prj, and click OK.
5. Click OK on the Create Mosaic Dataset tool window.

   The progress bar displays the status of the running tool.

   Once the process is complete, a pop-up message will appear.

   The AmbergOrtho mosaic dataset is created in the geodatabase and added to the ArcMap table of contents. This is an empty mosaic dataset. You will be adding raster datasets to it in the next steps.

When the mosaic dataset is added to the table of contents, it is added as a group layer. The top level has the name of the mosaic dataset—AmbergOrtho. There are also empty Boundary, Footprint, and Image layers.

Add rasters to the mosaic dataset

Steps:

1. In the Catalog window, under the ImageGDB, right-click the AmbergOrtho mosaic dataset you just created and click Add Rasters.

   This opens the Add Rasters To Mosaic Dataset tool.

2. In the Raster Type list, choose Match-AT.
3. Click the Properties button .

   The Raster Type Properties dialog box is opened. Here, you will enter specific information about the DEM and the location of the camera file.

4. Click the Properties tab.
5. Click the DEM radio button.
6. Click the browse button and navigate to C:\ArcGIS\ArcTutor\Raster\Data\Amberg_Scans\DEM.
7. Click the 01x01.flt file and click Add.
8. Click the Auxiliary Inputs tab.
9. Click the Camera browse button .
10. Navigate to C:\ArcGIS\ArcTutor\Raster\Data\Amberg_Scans\Match-AT Parameters, click the CAMERA file, then click Open.
11. Click OK to close the dialog box.
12. Click the Input browse button .
13. Navigate to C:\ArcGIS\ArcTutor\Raster\Data\Amberg_Scans\Match-AT Parameters\Amberg_MAT2.prj and click Open.
14. Click OK to run the tool.

    The progress bar displays the status of the running tool.

    Once the process is complete, a pop-up message will appear.

    The raster datasets are added to the mosaic dataset. The footprints are created for each raster dataset, and the boundary is generated for the entire mosaic dataset.

15. Ignore the warning message that appears.

    There are a few extra images defined in the Match-AT project file that are not included in the tutorial. These images are not added to the mosaic dataset. The list of missing images will be shown in the Results window.

16. Click the Full Extent button to view the mosaic dataset.
17. Uncheck the Image layer.

    This way, you are only looking at the footprints for each image. You can see how each footprint is not simply a rectangle representing the extents of a raster dataset. Instead, each footprint has a unique shape. This shape represents the warping applied by the image due to the orthorectification.

18. Uncheck the Footprint layer and check the Image layer.

    You can see the same shape in the mosaicked image as in the footprints. However, there is also a black line. This line represents the image boarder from the scanned images. To remove this boarder you will shrink the footprints. Fortunately, there are lots of overlap in the imagery; therefore, the shrinking will not result in a significant data loss. In fact, it is a common practice to crop aerial imagery.

Shrink the footprints

Steps:

1. Right-click the AmbergOrtho mosaic dataset in the Catalog window and click Modify > Build Footprints.

   The Build Footprints tool is opened.

2. Click the Computation Method drop-down arrow and click NONE.
3. Type 25 in the Approximate number of vertices text box.
4. Type 60 in the Shrink Distance text box.

5. Click OK to run the tool.

   The progress bar displays the status of the running tool.

   Once the process is complete, a pop-up message will appear.

6. Check the Footprint layer in the table of contents to see them.

   When looking at the dataset, you can see how the boarders of the images have been removed from the mosaicked image.

Build seamlines

Often, when working with aerial photography, you may want to control the resultant mosaicked image by defining the edge along which the images are mosaicked. You can do this by creating seamlines.

Learn about seamlines

Steps:

1. Right-click the AmbergOrtho mosaic dataset in the Catalog window and click Enhance > Generate Seamlines.

   The Build Seamlines tool is opened.

2. Click the Computation Method drop-down arrow and click RADIOMETRY.

   This option will examine the pixel values and patterns within the intersecting areas to compute the seamlines.

   
3. Click OK to run the tool.

   The progress bar displays the status of the running tool.

   Once the process is complete, a pop-up message will appear.

Update the mosaic dataset properties

Before looking at the results you should make sure the mosaic dataset properties are set to use the seamline.

Steps:

1. Right-click the mosaic dataset in the table of contents and click Remove.

   When you update the properties and add the mosaic dataset back to the display, the Image layer will reflect the updated properties.

2. Click the Catalog tab and expand the window.
3. Right-click the AmbergOrtho mosaic dataset and click Properties.
4. Click the Defaults tab.
5. Click the Allowed Mosaic Methods ellipse button .

   This opens the Configure Allow List dialog box.

6. Verify that the Default Method is Seamline and click OK.
7. Click the Default Mosaic Operator drop-down arrow and click Blend.

   This will blend the pixel values between overlapping rasters along the seamline. The default Blend Width is 10 and is also defined on this tab. This value defines the distance in pixels (at the display scale).

8. Click OK to close the dialog box.
9. Drag the AmbergOrtho mosaic dataset from the Catalog window and drop it on the display.
10. Uncheck the Footprint layer and check the Seamline layer.
11. Zoom in and around the seamlines. You can turn the seamlines on or off to examine the boundaries.

Build the overviews

To build a complete mosaic dataset you should build overviews. The overviews will be generated using the default mosaic method, which is Seamline.

Steps:

1. In the Catalog window, under the ImageGDB, right-click the AmbergOrtho mosaic dataset and click Optimize > Build Overviews.

   This opens the Build Overviews tool.

2. Accept the defaults and click OK.
3. Click OK to run the tool.

   The progress bar displays the status of the running tool.

   Once the process is complete, a pop-up message will appear.

The mosaic dataset has been created and is ready to publish as an image service using ArcGIS for Server. You can also use the mosaic dataset as a layer within ArcMap or ArcGlobe.