Block Adjustment window

The Block Adjustment window provides an interface for editing control points and performing quality control for the block adjustment computation. It allows you to edit tie points and ground control points (GCP), and provides access to the image block adjustment geoprocessing tools.

The minimum required inputs for the window are a mosaic dataset and the associated control point tables. Other optional inputs include the solution table, residual table, overlap polygon, and point coverage table, which are useful for identifying areas that need control points or finding and removing bad control points.

Accessing the Block Adjustment window

The Block Adjustment window is not shown in ArcMap by default. You will need to add the button to a toolbar so you can access it when you need it.

1. Click the Customize menu and click Customize Mode.
2. Click the Commands tab.
3. Scroll to the bottom of the Categories and choose Windows.
4. In the Commands, click and drag the Block Adjustment icon to any toolbar. Click Close to dismiss the Customize window.
5. Click the Block Adjustment icon to open the Block Adjustment window.

Block Adjustment user interface

The Block Adjustment window is composed of many parts: the Images, Overlaps, and Control Points tables, the geographic tiles of each of the highlighted controls points, and a set of tools on a toolbar.

The Images table shows you all the images that exist within the mosaic dataset. When you select an image, the Overlaps table lists the overlap combinations that exist for the selected image. When you choose an overlap scenario, the bottom part of the window will populate with the images that overlap. The Control Points table lists all the control points that exist for the Image ID that was highlighted.

There are many tools within the Block Adjustment window. Below are the descriptions of each tool.

Icon	Label	Description
	Add	Start a new point set, which will have a new point ID. Clicking a point from the image viewer will add a tie point. Clicking a point from map will add a ground control point.
	Edit	Move a control point from one place to another.
	Delete	Delete a control point. If the cursor is close to the point, it will be deleted when you click on the point. If you want to delete a whole point set that is associated with the point, press and hold the Shift key while clicking on the point. You can also select a point and use this button to delete the point.
	Save	Save the edits to the control point table.
	Stop editing	Stop the editing session.
	Select	Select a set of control points by clicking on any point within the set.
	Select by graphic	Select control points by drawing a polygon on the map.
	Zoom to point	Select the overlapped images based on the point on the map. It will zoom and center the map for each image in the image viewer.
	Zoom to resolution	Zoom to the image resolution for each image in the image viewer.
	Link viewer to map	Toggle between linking or unlinking the map and the image viewer.
	Reset	Reset the Block Adjustment window.
	Layer list	Choose the current mosaic dataset to use in the Block Adjustment window. The check box toggles the mosaic dataset's image on the display to on or off.
	Options	Bring up the window to set the default settings for the Block Adjustment window.
	Block adjustment tools	Click to open a block adjustment geoprocessing tool.
	Tie Points	Displays the tie points that are used within the Map.
	Center to selected tie points	Centers the Map around the selected tie points.
	Zoom to image resolution	Zooms to the image resolution for all images in the viewer.
	Set display scale	Use the scale bar to set the display scale for images in the viewer.
	Select blunder points	Select blunder points.
	Select ground control points	Select ground control points.
	Select ground control points by query	Select control point based on a user-defined query.
	Clear selected ground control points	Clear selected control points.
	Set a minimum residual value	Filter control points based on their residuals. A value of -1 will return all points.
	Ground Control Point IDs	Labels the ground control points with the appropriate Point ID.
	Residuals	Displays the residual vectors on the map. These arrows can be adjusted by using the scale factor. The size of the arrow will be residual * scale factor . The default scale factor is 15.

Block Adjustment Options

The Options window allows you to set default settings for your block adjustment workflow. There are three sections within the Options window: Default Dataset Names, Symbols, and Image Viewers.

The Default Dataset Names section allows the system to automatically reorganize these tables if they are in the same geodatabase as the mosaic dataset and have the suffixes specified in the defaults. You can also set the paths to the datasets if they have different names or are in different tables. These settings are stored in the register key, which won't change unless you click the Reset button. It is always recommended that you set the DEM for the area when you edit control points, since it is used as the Z-value for new points that are added.

The Symbols section allows you to customize the display symbols for tie points, ground control points, and selected control points. The Color By Rays check box will color code the tie points based on the number of rays within the tie point set.

Color of Rays based on the Count

Number of Rays	Color
2	Green
3	Blue
4	Pink
5	Yellow
6	Cyan
More than 7	Dark red

The Image Viewers section allows you to customize the image viewers using a fixed size, fixed number, or fit to display. Choose which option to use when displaying your image viewers:

• Fixed size—Choose this option if you want to display the image viewers in width and height.
• Fixed number—Choose this option to define the number of image viewers that will be used.
• Fit to Display—Choose this option to display all image viewers. This is the default.
• Display in Float Viewers—Choose this option to show the image viewers as stand-alone windows. You can position and resize the windows.

The Display Overlap Envelopes check box allows you to show the overlapping polygons in map view, where the polygons are rendered with different colors and sizes of outlines to denote the number of images in the overlapping polygon.

Workflow for using the Block Adjustment window

The following is an overview of steps for using the Block Adjustment window.

• Create tie points and ground control points from your mosaic dataset.
• Open the Block Adjustment window and set it up.
• Enter the ground control points.
• Edit the control points.
• Add tie points.
• Save your control points.

Set up the Block Adjustment window

Once you have created some control points and tie points, you can use the Block Adjustment window to perform a quality-control check.

1. Add the mosaic dataset to ArcMap.
2. Click the Block Adjustment window to open the Block Adjustment window. You can dock the window on the right side of ArcMap or drag the window to another monitor if you have dual monitors.
3. Select the mosaic dataset in the combo box and specify the control point table and other inputs.
   1. Click the Options button.
   2. Browse and set the corresponding tables.
      1. If all your tables are in the same geodatabase and use a mosaic dataset name plus a suffix for tables, the system can automatically detect the tables for the mosaic dataset. The default suffixes are _tiepoints, _controlPoints, _overlap, _coverage, _solution, _residual, and _DEM.

4. Click OK in the Options window.

   Once the dataset names are set, the Block Adjustment window will be active and ready to use.

Enter ground control points

There are three ways to add ground control points to the control point table, depending the type of ground control information you have:

• If you have georeferenced layers or maps as a ground control reference
• If you have a ground control point shapefile
• If you have georeferenced image chips or an image as a ground control reference

If you have georeferenced layers or maps as a ground control reference, use the following steps:

1. Add the georeferenced layers to ArcMap.
2. Make sure you have defined the DEM in the Block Adjustment Options window for your study area.
3. In the map, pan and zoom to find the location where you can enter a control point and click Zoom to point to center your map and image viewers to the point.
4. Optionally click Link viewer to map to link the map with image viewers so you can navigate the map and image viewers at the same time.
5. Click Add to start a new point set, click the map to enter a ground control point, and click the image viewers to enter the tie points.
6. Press the E key to end the point set.
7. Repeat the previous two steps to enter additional points.
8. Click the Save button to save the edits.

If you have a ground control point shapefile, use the following steps:

1. Prepare a point feature class (or point shapefile) from these coordinates.
2. Use the Append Control Points tool to append these points to the control point table.
   1. When you append your data, it is a good idea to use a DEM for accuracy.
   2. You can also use the tag field as the identification for the ground control points.
3. In the Block Adjustment window, click to sort by control points, and click the PointID column to sort by descending order. The added ground control points are on top.
4. Click each ground control point and the image viewers will display the overlapped images.
5. Right-click the ground control point row and choose Add to point set.

   

6. Click the image viewers to add tie points.
7. Press the E key to end this point set.
8. Click the Save button to save your edits.

Note:

If you have coordinates for only a small number of ground control points and these are not stored in a shapefile, you can enter them from the window by right-clicking on the map and entering the coordinates directly.

If you have georeferenced image chips or an image as a ground control reference, use the following steps:

1. Use the Compute Control Points tool to compute GCPs from the referenced image.
2. If you have a collection of image chips instead of one image, create a mosaic dataset from these images. Use the mosaic as a reference to compute GCPs.
3. Merge the result to the control point table using the Append Control Points tool.

Enter Checkpoints

Checkpoints are just like GCPs, which depict a known location onto the image. GCPs are used in the calculation of the block adjustment, but checkpoints are not used.

You can turn a GCP into a checkpoint if you do not want that particular point to be used in the block adjustment calculation. To change a GCP into a checkpoint, follow the steps below:

1. In the Control Point table, choose the row that you want to change from type GCP (to a checkpoint).
2. Right-click and choose Change Type.

The Type will now change to CHP (check point).

Edit control points

Some tie points used in the block adjustment might have large residual and RMS values. You can use the Block Adjustment window to examine and find high error points. You can then edit or delete them. There are a few ways to navigate to those potential points to edit:

• Select by control points.
• Sort by images.
• Select a point from map.
• Select spatially.
• Select by attribute.

You can select the control pointsyou want to edit.

1. Click the radio button to Select by control points.
2. Click the Residual column to sort by descending values; points that have a larger residual appear on top of the table.
3. Click each point set you want to examine. A point set is a set of points that all have the same PointID.
4. Examine the points in the pointID.

   • If a point needs to be moved—Click the Edit button and click the new location of the point. Optionally, you can use the number keys (4, 6, 2, 8) to finetune the location of the cursor.

   • If a point needs to be deleted—Click the Delete button and click the point to delete.
   • If a point set needs to be deleted—Click the Delete button and click on a point within the point set while holding the Shift key. Alternatively, right-click on the row in the control point table and access the context menu to delete a point or a point set.

You can select control points by sorting by images.

1. Click the radio button to sort by images.
2. Click the RMS column to sort by descending values; points that have a larger residual appear on top of the table.
3. Click an image that has a large RMS value.

   The Overlaps list box displays the combination of the images that overlap with the image you just chose.

4. Click a row.

   The overlapped images are displayed in the image viewers and the corresponding control points are displayed in the Control Points list box.

5. Click the control point to examine the accuracy.
6. Edit or delete the control points that will produce large residuals by clicking the Delete button.

You can select control points by selecting a point from a map:

1. Click the Select button and click a control point in the map display.

You can select images by spatially selecting a point on the display.

1. Click the Zoom to point button and click the map display.

   The overlapped images will be selected, based on the point where you clicked the map. It will zoom and center the map for each of the images in the image viewers.

Perform a query to select images by attribute:

1. Click the Query button, which is located above the control point list box.

   To remove the results from the query, click the Reset button.

Adding tie points

Sometimes the automatic tie point generation will not generate tie points for some areas. This may be due to images in different years or seasons, or there have been a lot of changes in the images. In these cases, you will need to use the Block Adjustment window to manually add tie points. There are two ways to identify areas that need more tie points:

• Visually examine the map view.
• Use the percentage of point coverage tool.

To visually examine where control points may be needed, you can look at the overlapping polygons and control point distribution in the map view.

1. Turn on the overlap feature class by enabling the Display Overlap Envelope check box in the Options settings.
2. In the map, find the areas that have fewer control points, based on the control points and overlapping polygons.
3. Use the Zoom and point button to zoom on each image within the viewers, to the location you clicked on in the main map display.
   1. Optionally click the Link view to map button. This allows you to zoom and pan the map and all the viewers simultaneously.
4. Click the Add button to start a point set with a new pointID. Then click the image viewers to create the tie points.
   1. If you need to add a point to an existing point set, right-click the row of the same point ID and choose to add to the point set.
5. Press the E key on your keyboard to end the point set.

Use the percentage of point coverage tool to identify where control points may be needed.

1. Click the radio button to sort by Images.
2. In the Images list box, click the column to sort by Coverage or #Points.
3. In the Overlap list box, click each row to display the overlapped images.
4. If you need to enter more tie points, continue with the steps below.
5. Click the Zoom and point button. This allows you to zoom each image viewer to the same location that was clicked on in the main map display.
   1. Optionally click the Link view to map button. Zoom and pan the map and the viewers simultaneously.
6. Click the Add button to start a point set with new pointID. Then click the image viewers to create the tie points.
   1. If you need to add a point to an existing point set, right-click the row of the same point ID and choose to add to the point set.
7. Press the E key to end the point set.

Save your control points

To save the points you finished editing, click the Save button. Click the Stop editing button to stop editing and to remove the locks on mosaic datasets and control point tables.

Here is a list of hotkeys and shortcut keys that can help you with editing.

Short cut	Description
E	End a point set.
Number key 4	Move cursor left.
Number key 6	Move cursor right.
Number key 2	Move cursor down.
Number key 8	Move cursor up.
Double-click on an image in the Images List box	A raster view with the image will pop up.