Create Digital Aerial Imagery Products ArcGIS Pro—Imagery Workflows

Available with Advanced license.

In ArcGIS Pro, you can photogrammetrically correct digital aerial imagery collected by a professional mapping camera to remove geometric distortions induced by the sensor and correct for terrain displacement. After addressing these effects, you can generate ortho mapping products.

In this tutorial, you will set up an ortho mapping workspace to manage your aerial imagery collection. Next, you will perform a block adjustment and review the results. Finally, you'll generate a digital surface model (DSM) and an orthorectified mosaic, or orthomosaic.

Computing the photogrammetric solution for aerial imagery is determined by its exterior orientation (EO), which represents a transformation from the ground to the camera and its interior orientation (IO), which represents a transformation from camera to image. Required exterior orientation parameters include perspective center (x, y, z), and Omega, Phi, and Kappa, and are provided in an Esri frames Table. Interior orientation parameters include focal length, pixel size, principal point, and lens distortion. This information can be found in the camera calibration report associated with your imagery and must be provided in an Esri Camera Table.

License:

ArcGIS Pro 2.6 or later is required to complete this tutorial.

Create an ortho mapping workspace

An ortho mapping workspace is an ArcGIS Pro subproject that is dedicated to ortho mapping workflows. It is a container within an ArcGIS Pro project folder that stores the resources and derived files that belong to a single image collection.

A collection of digital aerial images is provided for this tutorial. The tutorial data also contains frame and camera tables.

Download the tutorial dataset and save it to C:\SampleData\Aerial Imagery. If you save your data to a different location on your machine, make sure to update the path in each of the entries in the FramesTable file.
In ArcGIS Pro, create a project using the Map template and sign in to your ArcGIS Online account if necessary.
The default Parallel Processing Factor is set to 50%. In order to accelerate the adjustment process, you can increase the Parallel Processing Factor. Under the Analysis tab, click Environments. Locate the Parallel Processing parameter in the Environments window and enter 80% in the dialog box.
On the Imagery tab, in the Ortho Mapping group, click the New Workspace drop-down menu and select New Workspace.
In the Workspace Configuration window, enter a name for your workspace.
In the Type drop-down menu, choose Aerial - Digital.
In the Basemap drop-down menu, choose Topographic.
Click Next.
In the Image Collection window, under Exterior Orientation File / Esri Frames Table navigate to the tutorial data folder on your machine and select the Frames table file (FrameTable.csv). This table specifies parameters that are used to compute the exterior orientation (EO) of your imagery. In the block adjustment process, these approximate values are refined to achieve higher accuracy.
Make sure that the data paths listed in the raster column in the frame table file match the location of the image files on your machine.
Under Cameras, click the Import button , navigate to the tutorial data folder on your machine and select the camera table file (CameraTable). This file contains the interior orientation (IO) for the camera.

For this tutorial, the Esri frame and camera tables have been provided in the proper format. For other data sets, you will likely need to build and format these tables. For more information, see Frame and Camera tables.

Make sure the Spatial Reference and Camera Model are correct. The default projection for the workspace is defined based on your imagery. This projection must match the coordinates used in the frame table, and it determines the spatial reference for your ortho products, including the orthomosaic and DEM. For this dataset, we’ll use the default projection. Click Next.
Accept the default settings in the Data Loader window and click Finish.

If you have access to the internet, Elevation Source will be derived from the World Elevation Service. If you do not have access to the internet or a DEM, choose the Constant Elevation option from the drop-down menu and enter an elevation value.

Once the workspace has been created, the images and image footprints will be displayed. An Ortho Mapping category has also been added to the Contents pane. The source imagery data and derived ortho mapping products will be referenced here.

The initial display of imagery in the workspace confirms that all images and necessary metadata were provided to initiate the workspace. The images have not been adjusted, so the alignment is only approximate at this stage, and the mosaic may not look correct.

Block Adjustment

The next step is to perform block adjustment using the tools in the Adjust and Refine groups. The block adjustment will first calculate tie points, which are common points in areas of image overlap. The tie points will then be used to calculate the orientation of each image, known as "exterior orientation" in photogrammetry.

In the Ortho Mapping tab, in the Adjust group, click Adjust .
Perform Camera Calibration should be unchecked by default for digital aerial imagery, as most airborne sensors have been calibrated and provide accurate interior orientation values in a camera calibration report. Automatic camera calibration is typically applied to other types of data, like low-cost drone cameras, to compute and improve the camera’s geometric parameters, while simultaneously determining image orientation and image ground coordinates.
Accept all remaining default settings and click Run to perform block adjustment.
After the adjustment is complete, turn on the Tie Points layer in the contents pane to view the distribution of generated tie points on the map.
Tie point residuals or accuracy reporting can be viewed in the logs file. In the Ortho Mapping tab, in the Review group, click Logs to access this file. The units for tie point Root-Mean-Square Error (RSME) is pixels.

Review adjustment results

In the Ortho Mapping tab, in the Review group, click Adjustment Report to generate adjustment statistics. The adjustment report provides a record of the adjustment and overall quality measures of the process.

Generate a digital elevation model (DEM)

The stereo image pairs of an image collection are used to generate a point cloud (3D points) representing the 3D positions for each of the tie points extracted from the imagery for which elevation data can be derived. The derived elevation data may be either a digital terrain model (DTM), which includes an estimate of the ground surface, or a digital surface model (DSM), which includes the elevations of trees, buildings, and other above ground features.

Note:

If an area is heavily wooded, or has other dense vegetation cover, it will not be possible to derive a DTM ground surface because the ground is not visible. This issue might also arise in dense urban areas, where buildings obscure the ground. In these cases, the most appropriate elevation surface is a DSM, which specifically creates a surface depicting the top of the urban environment.

In the Ortho Mapping tab, In the Product group, click DEMs to start the DEMs Wizard. Click Next.
In the Point Cloud Settings window, for Matching Method, choose Semiglobal Matching from the drop-down menu. This method is typically used for images of urban areas and captures more detailed terrain information.
Make sure Filter Ground Objects is checked.
For Maximum Object Size to Filter, use the default value of 10 meters. Objects smaller than this threshold will be filtered out and the elevation of nearby ground points will be used to interpolate the ground surface; otherwise, larger objects will be treated as above-ground features, such as buildings, bridges, or dense vegetation.
Leave Point Ground Spacing blank. This defines the spacing, in meters, at which the 3D points are generated. The default is five times the resolution of the source imagery.
Accept all remaining default settings and click Next.
For information on the Advanced Settings, see Generate elevation data using the DEMs wizard.
In the DEM Interpolation Settings window, under the Surface Type drop-down menu, choose Digital Surface Model.
For Cell Size, use the default value of 5 x GSD. This will determine the resolution of the DSM (five times the imagery resolution).
Accept the remaining default settings and click Finish. This process will take some time to complete.

Generate an orthomosaic

Next, you will generate an orthomosaic. An orthomosaic is an orthorectified image product mosaicked from an image collection. Geometric distortion has been corrected and the imagery has been color balanced to produce a mosaic.

In the Ortho Mapping tab, In the Product group, click Orthomosaic to start the Orthomosaic Wizard.
Click Next.
In the Orthorectification Settings window, under Elevation Source, select DSM. This is the elevation product that was just generated.
In the Color Balance Settings, uncheck Select Mosaic Candidates and accept all other default options. Click Next.
In the Seamline Settings window, under the Computation Method drop-down menu, choose Voroni. Click Next.
In Orthomosaic Settings window, for Pixel Size, use the default value. This will determine the final resolution of the orthomosaic.
Click Finish to generate the final orthomosaic. This process will take some time to complete.

Summary

In this tutorial, you created an ortho mapping workspace for digital aerial imagery and used tools in the Ortho Mapping tab to apply a photogrammetric adjustment. You then used the Ortho Mapping Products Wizard to generate a DSM and an orthomosaic. For more information on these topics, see the following:

The aerial imagery used in this tutorial was acquired and provided by Vexcel Imaging GmbH.