Available with Advanced license.
Block adjustment is the process of computing an adjustment or transformation based on the internal relationship between overlapping images, control points, a camera or sensor model, and a digital elevation model (DEM). After performing a block adjustment, it is necessary to review the results of the adjustment and assess the quality of the control points (ground control points [GCPs], tie points, and check points) used in the adjustment. A summary of the results are displayed in the Adjustment Report window in the Review group on the Ortho Mapping tab.
Use the adjustment report to assess the number of control points used in the adjustment, the areas of the image collection where control points and overlap are sufficient or lacking, and the reprojection error in the images.
Note:
The adjustment report .html file, initial and adjusted GCP positions shapefiles, and tie point matches shapefiles are stored in the Project folder at \ArcGIS\Projects\[project name]\OrthoMapping\[ortho mapping workspace name].eomw\Reports\.
Note:
When a tie point set is identified in overlapping images, the 3D coordinates of the corresponding point can be calculated in the block adjustment. The 3D point is then reprojected on all the images it intersects, and the distance between the reprojected point and the initial tie point is called the reprojection error.
Adjustment Summary table
The Adjustment Summary table provides a synopsis of your most recent block adjustment. The fields in the Adjustment Summary table are described as follows:
| Field name | Description |
|---|---|
Project Name | Name of the ortho mapping workspace. |
Report Time | Date and time the report was generated. |
Number of Input Images | Number of images in the collection used in the ortho mapping workspace. |
Number of Adjusted Images | Number of images adjusted in the block adjustment. |
Number of Tie Points | Number of tie points used to perform the block adjustment. |
Number of Solution Points | Number of solution points generated in the block adjustment. |
Reprojection Error (pixel) | The root mean square error (RMSE) of the reprojection across all adjusted images. The units are pixels. Each computed 3D point has initially been detected on the images (2D keypoint). On each image, the detected 2D keypoint has a specific position. When the computed 3D point is projected back to the images, it has a reprojected position. The distance between the initial position and the reprojected one gives the reprojection error for the tie point. |
Ground Resolution (m/pixel) | Average ground resolution for all images in the image collection. The units are listed in the field heading. |
Adjustment Type | Adjustment type used in the adjustment. The options are as follows:
|
Ground Control Points involved in Adjustment | Indicates whether GCPs were used in the adjustment. |
Summary of Quality Checks table
A summary of the quality and types of checks to assess the quality of the project are listed in the Quality Checks table, as described below.
| Field name | Description |
|---|---|
Tie Point Mean Reprojection RMSE (pixel) | Root mean squared error (RMSE) of the tie point mean reprojection in the adjustment. For most nadir frame camera cases, this value should be smaller than 0.5 pixel. For oblique cases, less than 1.0 pixel is acceptable. If the tie point mean reprojection RMSE is larger than 1 pixel, it may mean that camera calibration is not accurate. For example, camera might be a rolling shutter type, but adjustment doesn’t enable rolling shutter mode. Or the initial input camera focal length, or pixel size, is not correct. |
Calibrated Images | Number of images that are successfully involved in adjustment, so that image exterior orientation parameters and interior orientation parameters are accurately optimized. Check is passed |
Camera Calibration (Focal Length (mm)) | The comparison between input or initial camera focal length, and optimized focal length from adjustment. A difference less than 25% means camera calibration converges to an optimized value close to input focal length. Otherwise there might be blunders in input focal length or pixel size. |
Mean Number of Tie Point Observations | The ratio between number of tie points and number of solution points. It records the average number of images that can observe one solution point. It reflects the configuration of the flight. An ideal image collection should have a value larger than 3. A mean number of tie point observations less than 2.5 usually means the overlap between consecutive images is not sufficient. |
Ground Control Points Involved in Adjustment | If there are GCPs used to georeference the project, RMSE of GCP residuals in X, Y, and Z are listed. Check is passed |
Check Points for Accuracy Assessment | If there are check points used to evaluate the absolute accuracy of adjustments, the RMSE of check point residuals in X, Y, and Z are listed. Check is passed |
if 95% or more images are calibrated. There might be blunders in the input images or camera parameters if less than 50% images are calibrated. For example, more than half of the images are covered by water body.Summary of Tie Points table
For every adjusted image, a given number of tie points were used to perform the adjustment. The fields in the Summary of Tie Points table are described as follows:
| Field name | Description |
|---|---|
Min | Minimum number of tie points used in an image adjustment for the image collection. |
Max | Maximum number of tie points used in an image adjustment for the image collection. |
Median | Median number of tie points used per image adjustment for the image collection. |
Average | Average number of tie points used per image adjustment for the image collection. |
Distribution of Tie Point Residuals table
This table lists the number and percentage of tie points falling in each residual interval for 0.2 pixel. A good adjustment should have 90% of tie points below residual at 1 pixel.
Summary of Solution Points table
Tie points connecting two or more images are called multirays and are essential for aerial triangulation. This summary table lists the number of multirays detected and used in the adjustment. The number of 2-Rays is the number of 2-point tie point sets, or the number of tie points that connect two overlapping images. The number of 3-Rays is the number of 3-point tie point sets, or the number of tie points that connect three overlapping images, and so on. Adjustment quality is better when there are numerous multirays with many overlapping images.
Tie Point Projection Error Per Image table
This table lists the reprojection error for tie points in each image. The fields in the Tie Point Projection Error Per Image table are described as follows:
| Field name | Description |
|---|---|
Image ID | Image identification number. This is the same value as the OBJECTID field in the mosaic dataset footprint table. |
Image Name | Name of the image in the collection. This is the same value as the Name field in the mosaic dataset footprint table. |
Number of Tie Points | Number of tie points used to adjust the image. |
Mean Reprojection Error (pixel) | Average reprojection error across all tie points in the image. The units are pixels. |
Camera Calibration table
This table lists the camera calibration information for the adjustment. This information is either provided with the cameras tables when configuring the ortho mapping workspace or calculated when you check Perform Camera Calibration on the Adjust dialog box.
The table is only listed in the report for aerial and drone imagery. The fields in the Camera Calibration table are described as follows:
| Field name | Description |
|---|---|
Focal Length (mm) | Camera lens focal length in millimeters. Comparison of adjusted focal length and initial focal length from exif or other metadata. |
Principal Point X (mm) | The principal point is a point on the image plane where a line from perspective center (camera lens), perpendicular to the image plane, intersects the image plane. The X direction is parallel to the direction of image rows. |
Principal Point Y (mm) | The principal point is a point on the image plane where a line from perspective center (camera lens), perpendicular to the image plane, intersects the image plane. The Y direction is parallel to the direction of image columns. |
Distortion Parameters | Lens distortion parameters, defined by the Brown-Conrady Model. |
Pixel size (um) | Size of a pixel on the focal plane of the sensor. |
Images Used vs Total | Number of images used in the camera calibration, and the total number of images in the project. |
GPS Positioning Deviations table
This table shows the adjusted image positioning change (in meters) if the initial position information from the GPS is available. The minimum, maximum, median, and average deviation statistics across all images are listed at the bottom of the table. The table is only listed in the report for aerial and drone imagery. The fields in the GPS Positioning Deviations table are described as follows:
| Field name | Description |
|---|---|
Image ID | Image identification number. This is the same value as the OBJECTID field in the mosaic dataset footprint table. |
dX (m) | Image shift in the X direction from the initial position. The units are meters. |
dY (m) | Image shift in the Y direction from the initial position in meters. The units are meters. |
dZ (m) | Image shift in the Z direction from the initial position in meters. The units are meters. |
Initial GPS Positions and Adjusted Positions graphic
This graphic shows a scalar representation of the GPS deviations for each image. Red points indicate the initial position of the images from the GPS, and gray vectors indicate the magnitude of the positioning deviation as a result of adjustment. The vectors are exaggerated for visualization. When viewing this graphic, assess the directional shift of the images in your image collection to evaluate systematic error in the adjustment. Cyan square points indicate the dropped/removed images that are not involved in adjustment. The graphic is only listed in the report for aerial and drone imagery.
Cross Matches graphic
This graphic indicates the level of connection between images. Green points are the image positions after bundle adjustment, and a link between two images indicates that tie point sets were identified between the images. A link with a dark color indicates a larger number of tie point sets and a stronger connectivity between the images. Identify areas in your image collection where tie points are sufficient or lacking, and use this information to add control points or overlapping images if necessary. The graphic is only listed in the report for aerial and drone imagery.
Overlap Map graphic
This graphic is a static map of the overlap between images. Higher numbers of overlapping images produce higher accuracy for three-dimensional ortho products. You can use this graphic to identify areas in your image collection that may require additional overlap, or to better understand the accuracy of your adjustment.
Ground Control Points Summary table
This table shows an overall summary of the GCPs used in the block adjustment. It is only listed in the report if you used GCPs in the adjustment. The fields in the Ground Control Points Summary table are described as follows:
| Field name | Description |
|---|---|
Number of Input Ground Control Points | The total number of Ground Control Points in the GCPs feature class in the ortho mapping workspace. |
Ground Control Points Involved in Adjustment | The PointID value of the GCPs used to perform the block adjustment. This is the same value as the PointID field in the GCP attribute table. |
Minimum Number of Observations | The minimum number of tie points linking overlapping imagery to a GCP. |
Maximum Number of Observations | The maximum number of tie points linking overlapping imagery to a GCP. |
Average Number of Observations | The average number of tie points linking overlapping imagery to a GCP. |
Ground Control Point Deviations table
This table shows the adjusted positioning change (in meters) of the GCPs if GCPs were used in the adjustment. It is only listed in the report if you used GCPs in the adjustment. The fields in the Ground Control Point Deviations table are described as follows:
| Field name | Description |
|---|---|
Point ID | The PointID value of the GCP. This is the same value as the PointID field in the GCP attribute table. |
dX (m) | Shift in the X direction from the initial position of the GCP. The units are meters. |
dY (m) | Shift in the Y direction from the initial position of the GCP. The units are meters. |
dZ (m) | Shift in the Z direction from the initial position of the GCP. The units are meters. |
The minimum, maximum, median, and average directional shift values for each direction are listed at the bottom of the table. The RMSE of the shift across all GCPs is also listed.
Ground Control Points Reprojection Residual table
This table shows the directional residual error of the reprojected GCPs in each image. The fields in the Ground Control Points Reprojection Residual table are described as follows:
| Field name | Description |
|---|---|
Point ID | The PointID value of the GCP. This is the same value as the PointID field in the GCP attribute table. |
Image ID | Image identification number. This is the same value as the OBJECTID field in the mosaic dataset footprint table. |
Residual X (pixel) | The residual error in the X direction of the adjusted position of the GCP. The units are pixels. |
Residual Y (pixel) | The residual error in the Y direction of the adjusted position of the GCP. The units are pixels. |
Check Point Deviations table
This table shows the adjusted positioning change of the check points if check points were used to assess the accuracy of the adjustment. It is only listed in the report if you changed some GCPs to check points before the adjustment. The fields in the Check Point Deviations table are described as follows:
| Field name | Description |
|---|---|
Point ID | PointID value of the Check Point. This is the same value as the PointID field in the Check Point attribute table. |
dX (m) | Shift in the X direction from the initial position of the check point. The units are meters. |
dY (m) | Shift in the Y direction from the initial position of the check point. The units are meters. |
dZ (m) | Shift in the Z direction from the initial position of the check point. The units are meters. |
The average directional shift for all the checkpoints and the RMSE of the directional shift are listed at the bottom of the table.