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Block adjustment

When an ortho mapping workspace is created, the next step is to perform block adjustment using the tools in the Adjust and Refine groups. The adjustment tools encapsulate operations of computing match points (tie points) from overlapped images and performing triangulation calculations. The adjustment tools use an algorithm and processing procedure that are suitable for each ortho mapping workspace type. For instance, the algorithm performs RPC triangulation for satellite images and frame triangulation for aerial images. The parameters used in the adjustment computation can be defined on the Adjustment Options dialog box. The adjustment quality report can be viewed using the Quality Report tool.

Adjust and Refine tools Review group

Adjust tools

The Adjust tool Adjust is used to perform block adjustment of the image collection in the current ortho mapping workspace. The processing is always done at image source resolution—computing tie points from source images, and then performing triangulation using the computed tie points. Drone and scanned aerial images normally come with poor-quality or no exterior orientations and coarse GPS information. In these cases, an initial adjustment will be performed at a coarse resolution—a user-defined pyramids level is used to estimate the image orientations, and then an adjustment will be performed at the source resolution. The tie points generated at the initial adjustment will be used to seed the tie point computation and triangulation calculation at the source resolution in the refined Adjust calculation. Having pyramids built for the image collection ahead of time or during ortho mapping workspace creation will reduce the time of initial adjustment process.

Adjustment Options

The parameters used in computing the block adjustment are defined in the Adjustment Options Adjustment Options dialog window. These include point density, relative accuracy of source imagery and computed adjustment points, and other parameters as described below. The appropriate set of parameters are presented in the dialog window depending on the type of workspace specified. For example, the set of parameters for a workspace defined for satellite imagery differ from those specific to drone imagery.

Quick Adjust

The Quick Adjust tool Quick Adjust is applicable for processing drone images. It performs adjustment at a coarse resolution to estimate exterior image orientations and improve GPS location. This initial adjustment is done quickly and allows you to get an understanding of the data coverage of your study area and the choice of the processing parameters for this collection before taking the time to run a more accurate refined adjustment at source resolution. For example, when you collect data in the field, you can run this Quick Adjust tool for an initial assessment of the adjustment, then run Adjust again to compute the full adjustment. This can also be used as a step to establish the camera model before adding GCPs.

Adjust

To further improve the adjustment accuracy with ground reference, you can add ground control points (GCP) using the Manage GCP tools Manage GCPs in the Refine group. The adjustment quality can be viewed from an adjustment report using the Adjustment Report tool. If the adjustment errors are larger than expected, there are several ways you can check your tie points:

  • Check the solution point layer in the Content pane, review the residual map or analyze the residuals in the Residual field in the attribute table, identify point IDs that have large residuals, and delete tie points that have the same point IDs in the control point table.
  • Run the Analyze Tie Point tool to generate a coverage feature class and an overlap polygon feature class. The two feature classes help you understand whether you have enough tie points and where you need to add more tie points.
  • Use the Recompute Tie Points tool to compute tie points and to also append more tie points.

These tools will update the control points in the ortho mapping workspace. You can run the Adjust tool again to perform triangulation and update the image collection.

Refine Adjustment

To further improve the adjustment accuracy with ground reference, you can add ground control points (GCP) using the Manage GCP tools. The adjustment quality can be viewed from an adjustment report using the Adjustment Report tool. If the adjustment errors are larger than expected, there are several ways you can check your tie points:

  • Check the solution point layer in the Content pane, review the residual map or analyze the residuals in the Residual field in the attribute table, identify point IDs that have large residuals, and delete tie points that have the same point IDs in the control point table.
  • Run the Analyze Tie Point tool to generate a coverage feature class and an overlap polygon feature class. The two feature classes help you understand whether you have enough tie points and where you need to add more tie points.
  • Use the Recompute Tie Points tool to compute tie points and to also append more tie points.

These tools will update the control points in the ortho mapping workspace. You can run the Adjust tool again to perform triangulation and update the image collection.

GCP Manager

The GCP Manager pane is used to add, edit, and manage your control points so they can be used in your ortho mapping project. If your GCP Manager does not have any rows in the table, it means that there are currently no GCPs or tie points associated with your ortho mapping project. If you already have GCPs saved in a file, then you can import them using the Import GCPsImport GCPs button. If you do not have a GCP file, you can create GCPs using Compute GCPs Compute GCPs, which is located under the Manage GCPs drop down menu. You can also create new GCPs and tie points using the Add GCP or Tie Point Add GCP or Tie Point tool.

The table below lists all the tools you can use within the GCP Manager pane. For the full workflow to add GCPs, see Add GCPs to your ortho mapping workspace.

IconNameDescription
Add GCP or Tie Point

Add GCP or Tie Point

Create a GCP by clicking a location on the map. Then add the corresponding tie points in the GCP Manager viewer.

Clear Links

Clear Links

Delete all the links between the images, for the selected ground control point.

Delete GCP

Delete GCP

Delete the selected ground control point.

Delete All

Delete All

Delete all the ground control points.

Import GCPs

Import GCPs

Import a GCP file from a text file, a CSV file, or a feature class.

The feature class must have x, y defined in either the Shape field or in two separate fields.

Export GCPs

Export GCPs

Export the GCPs to a file.

Filter

Filter

Toggle the filter button to show all the GCPs, or only the GCPs in the current map display. The default is to show all GCPs.

Click the Filter button to filter out GCPs that are outside of the current extent. This can be used when GCPs are outside of the area of the image collection, or used to focus on one GCPs within area of interest.

Refresh

Refresh

Refresh the GCPs in the GCP Manager and the map display.

This is useful when you make an edit to a GCP, to make sure that the manager and the map display are still in sync.

Full Extent

Zoom

Zoom to the full extent of the image.

Show GCP

Show GCP

Display the corresponding GCP location in the image display window.

DRA Image Analysis

Dynamic Range Adjustment

Adjust the stretch, only using the data contained within the image display window.

To temporarily disable a GCP, change the XY Accuracy and Z Accuracyfields to <NA>.

If you want to change a GCP into a check point, right-click on the GCP row in the table, and choose Change to Check Point.

The image viewer in the GCP Manager pane is able to use dynamic range adjustment (DRA) to display the image. Press Ctrl + D to toggle DRA on and off.

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