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Mosaic Tool - Manual Mosaicking in Geomatica 2018

PCI Geomatics -

In Geomatica 2018 mosaicking changed from previous versions to a standalone tool on the Geomatica toolbar - Mosaic Tool. The Mosaic Tool allows the user flexibility to prepare, edit and create a seamless mosaic.

You can follow this tutorial if your Geomatica licensing for Mosaic Tool does include the Automatic Mosaicking tools included with the Ortho Production Toolkit module. In the manual mosaicking workflow we will manually define the preparation of the mosaic, which consists of editing image order, adding and computing cutines, applying normalization and color balancing.

Section 1 of this tutorial outlines the different methods of initializing a mosaic project: OrthoEngine or Mosaic Tool. Once the mosaic project is created, all editing and generating of the final mosaic is completed in the Mosaic Tool.

Mosaic Tool Interface

Icons in the Toolbar

1. Open Mosaic Tool and Add Source Images

1.1 OrthoEngine

1.2 Geomatica Toolbar

2. New Project Wizard

2.1 Source Images

2.2 Mosaic Definition

3. Edit Image Order

4. Edit Cutlines

4.1 Drawing a Cutline

4.2 Edit a cutline

4.3 Adjust Blend Width

5. Adjust Normalization

6. Edit Colour Balancing

7. Add Source Images to Mosaic

8. Restore Images to Source

9. Additional Tools

9.1 Quality Control Layer

9.2 Verification

9.3 Mosaic Overview Window

Mosaic Tool Interface

The Mosaic Tool is the third icon on the Geomatica toolbar.

 

You can work on the entire mosaic or, with a larger mosaic project, work with a subset of the mosaic images that you open from the Mosaic Overview window.

The following figure identifies the basic elements you will work with in the Mosaic Tool window. Information about the Mosaic Tool menus, toolbars, control pane and view pane are available from the Geomatica Help – Mosaic Tool > About the Mosaic Tool window.

Icons in the Toolbar

 Button

 Label

 Description

 

New Project

Create a new mosaic project.

For information about creating a new project, see Creating a new mosaic project.

 

Open

Open a mosaic project, add source images to a project.

 

Save Project

Save the active mosaic project.

 

Mosaic Overview

Opens the Mosaic Overview window, in which you can view an overview of your mosaic and work with a subset of images in your mosaic.

 

Undo / Redo

Cancels or restores the last action.

 

Zoom To Overview

Zooms to display the entire image in the View pane.

 

Zoom Interactive

Zooms in on the user-defined area of the image. Click and drag an area of the screen to define the zoom area.

 

Zoom In / Out

Zooms in or out of an image.

 

Zoom 1:1

Zooms to a 1:1 resolution of the current image.

 

Pan

Enters pan mode, allowing you to dynamically move the image around the View pane. Click and drag to move the image.

 

Enhancements

Applies enhancement options to the currently selected image or layer. Options include: None, Linear, Root, Adaptive, Equalize, Infrequency, Tail Trim, Exclude Min/Max, Set Trim %

 

Contrast

Controls the difference between the light and dark extremes for all images displayed.

 

Brightness

Controls the overall luminosity (amount of light) for all images displayed.

 

Normalization

Applies normalization options to all images displayed.

Options include: None, Hot Spot, Adaptive Filter

 

Color Balancing

Allows you to apply a global or single color balance function.

Options include: None, Manual Area, and Overlap Area. The "Match Area" option is available only if match area shapes exist for the selected or active image.

 

Cursor Control

Displays the Cursor Control window, allowing you to define the cursor position in three different coordinate systems: raster, geocoded and in a user-defined projection. You can move the cursor in any of the supported coordinate systems by changing the associated coordinates.

 

RGB Mapper

Opens the RGB Mapping window.

 

Collection Viewer

Opens the Collection Viewer window, which allows you to work on the currently selected or active image.

 

Vector Editing

Displays the Vector Editing toolbar, allowing you to modify existing cutlines, exclusion masks, and match areas in the pixmap.

Options include: Find, Reverse Vertices, Add Vertices, Start Vertex, Previous Vertex, Midpoint, Next Vertex, End Vertex, Show Vertices, Vertices Information

 

New Cutline

Enters vector editing mode, allowing you to define new cutlines. Applies to the currently selected or active image.

Options include: Polygon, Rectangle, Ellipse

 

New Mask

Enters vector editing mode, allowing you to create a new exclusion mask for color balancing. Applies to the currently selected or active image.

Options include: Polygon, Rectangle, Ellipse

 

New Match Area

Collect polygons for the active image that will be used to apply a manual color balance function.

 

Map Layer Selection

Allows you to select a raster image layer in the View pane. The selected layer appears highlighted in the Control panel.

  • Single-click to select the top-most raster at the cursor location
  • Click-and-drag to select all layers touched

Control-click to select multiple images

 

Flash Selected Map Layers

Allows a selecting image in the Mosaic Viewer or in the tree list to flash for easy recognition.

 

Image Status

Allows you to set the status of a selected image or images. Options include: Verified, Unverified.

 

Add Image To Mosaic

Adds the active or selected layers to the output mosaic file.

Mosaic Overview Window

There are a number of options available from Mosaic Tool > Tools > Options. A particularly useful option is Performance – Bypass Mosaic Overview… When opening a large mosaic project, the mosaic overview window will open instead of automatically loading all of the images into the Mosaic Tool (which can be time consuming). You can change the image threshold at which the Mosaic Overview window appears when you open a mosaic project. See section 7.3 Mosaic Overview Window for more information

1. Open Mosaic Tool and Add Source Images

There are three methods of initially creating a mosaic project:

  1. OrthoEngine – If your data needs to be orthorectified, complete an orthorectification workflow in OrthoEngine first. The Mosaic Tool can then be opened from the Mosaic OE step.
  2. Mosaic Tool (Geomatica Toolbar) – If your data is ready to be mosaicked, open the Mosaic Tool directly from the Geomatica toolbar and load prepared images.

1.1 OrthoEngine

If you generated orthorectified images in an Orthoengine project, you can open the Mosaic Tool from Orthoengine.

  1. From the Mosaic Processing Step, click Mosaicking

 

  1. The Mosaic Tool opens and your ortho images will be automatically loaded into the New Project Wizard.

1.2 Geomatica Toolbar

If you have images that are ready to mosaic, you can open the mosaic tool directly from the Geomatica Toolbar.

  1. Once the Mosaic Tool opens, click New Project to open the New Project Wizard
  2. The Source Images window is the first window in the Wizard. Click Open to select images that you want to add to the mosaic project.

2. New Project Wizard

Whenever a new project is started the New Project Wizard is automatically opened. The three windows of the New Project Wizard are outlined in detail below.

2.1 Source Images

On the Source Images page of the New Project Wizard window, select the images you want to include in your mosaic and, if necessary, enter a NoData value for the source images.

After you select the source images you want, they appear in the Source file list box. For now, only the footprints appear but you will see your imagery later, when you generate the mosaic preview.

For information on the toolbars in the New Project Wizard, please see the Geomatica Help - New Project Wizard toolbars

  1. If you created a new project in the Mosaic Tool you will need to add the source images, by clicking the Open button.
  2. If you opened the Mosaic Tool from OrthoEngine, the images will already be loaded
  3. Add or remove images as required and then click Next

2.2 Mosaic Definition

After you add the source images you want to use, your next step is to enter information about the output mosaic file. You can specify the following information in this panel

  • Mosaic output
    • Single File - well suited for use with smaller, less complex projects. The entire mosaic is written to an individual file with a tile-definition layer of only one polygon shape.
    • Tiled - well suited for use with larger, more complex projects. That is, when mosaicking large volumes of data, it is more practical to create the mosaic as a series of smaller tiles rather than one (potentially) large file.
    • Defined by polygons - uses a file you specify that has an existing vector-polygon layer containing the tile definitions you want to use for the mosaic.
  • Output file name and format
    • The name you enter for Output file will be the file name of the mosaic according to the format you select. For example, <file_name>.pix or <file_name>.tif, as applicable
  • Channels, and Channel mapping
    • Original channel number is based on your source images. You can enter a different number of channels for the output mosaic (typically, this is to reduce the number of channels). You can also map the channels between the input and output images.
  • Output NoData
    • You can enter one or more NoData values in the output imagery. For example, to specify that channel 1 has a NoData value of -9999, channel 2 is 0 and channel 3 is 255, enter -9999,0,255. You can also skip a channel. For example, channel 1 has no defined NoData value, but you want to use 0 and 255, respectively, for channel 2 and channel 3, enter ,0,255 (notice the comma before the zero).
  • Mosaic extents and Mosaic size
    • You can change the extents by selecting a file or by dragging the blue Mosaic Extents polygon in the viewer. You can also specify the mosaic size to adjust the blue extents rectangle
  • Pixel size (x and y)
  • Projection Information
    • Select the projection type (Pixel, UTM, Long/Lat, Meter, SPCS, Other) and then enter the correct projection string
  • Bounds and UL, LR coordinates
    • Select Geocoded (easting, northing) or Geographic (latitude, longitude) to specify how to display the coordinates of the mosaic file
    • If necessary adjust the UL and LR coordinates based on the coordinate system

Enter the correct information for all of the Mosaic definition options and then Click Finish - The source images will be added to the mosaic tool and the output mosaic file will be defined.

3. Edit Image Order

The order of the images in the Source Images list is determined by the Sort method that you specified in the Mosaic Preparation. You can change the order of the images by holding and dragging the images in the sources images list to change the order that they appear in the mosaic. As you move the images in the list, the mosaic preview will be updated to show the changes

You can also change the image Z-Order. Right-click on an image in the Source Images list and click Properties. The Z-Order of the image is in the General tab. In the Z-order box, you can type or select a number to indicate the order in which the image will be added to the mosaic. A higher value represents top-most positioning. The mosaic image always has a z-order value of zero, meaning it is at the bottom of the image "stack".

4. Edit Cutlines

When you create a mosaic, you want to crop the images so the best portions of the images are seamlessly joined together. A cutline is a polygon that outlines the portion of an image that will be used in the mosaic. 

You can edit the cutlines to ensure that the seams between the images are not as noticeable. Editing the cultines can be done in the Mosaic Tool or in the Collection window. The Collection Viewer window in the Mosaic Tool provides a full-resolution, close-up view of the active (working) image, allowing you to generate or refine cutlines and match areas in the entire image, using a 1:1 resolution view. In this window, cutlines are drawn on top of the image, with the entire image being displayed by default.

The extents of this window are defined by the active image. All neighboring images are displayed, but you can toggle their display on or off using the toolbar buttons. You can also change the layering order the displayed images by changing their order in the Image Tree List.

Cutlines should avoid:

  • buildings or man-made features, since they may lean in different directions in the imagery
  • large bodies of water, because waves may look different in different images, and water tends to have different color in different images
  • areas that are significantly different in color and texture, such as forests and cultivated land, since they may look different from image to image

4.1 Drawing a Cutline

We will first create the cutline in the manual mosaic window and then open the collection viewer window to examine the cutline.

  1. Select the bottom image by clicking on the file in the files tree.
  2. Click on the New Cutline icon . The dropdown menu includes Polygon, Rectangle and Ellipse options.
  3. Position the cursor where you want to begin collecting the cutline.
  4. Draw a polygon around the part of the image that you want to be included in the mosaic.
  5. Make sure to include only the best sections of the image while retaining an overlap between the images. Once you have outlined a cutline polygon, hit the Enter key or double click to close the cutline. You can use the undo toolbar button to remove a bad cutline. 

 

  1. You can then continue to collect cutlines for the other images.

4.2 Edit a cutline

  1. To edit a cutline select an image from the Source Images list. You can expand the image to ensure that the cutline is currently visible

 

  1. On the toolbar click the vector editing icon  to open the vector editing toolbar

 

  1. Select one of the image cutlines using the Find tool 
  2. Two different representations for cutlines are shown – a solid line and a dotted line.
  • A solid cutline represents a cutline on the top of the image
  • A dotted cutline represents a cutline underneath an image

 

  1. Zoom into a section of the image where you want to adjust the cutline. In the example below, we can edit the cutline to pass around the water and not through the water.

 

  1. Select the Reshape tool from the Vector Editing Toolbar 
  2. Click on the image near a cutline where you want the new reshaped cutline to be placed.
  3. Continue to click along the feature in the image where the cutline should be located.
  4. Click enter once you are done editing to exit the reshaping tool

 

  1. You can also add vertices  or move specific vertices by selecting them with the Find tool and dragging them to a new location.

4.3 Adjust Blend Width

You can reduce the appearance of seams by blending the pixel values on either side of the cutline to achieve a gradual transition between the images. That is, blending "softens" the appearance of the seams such that the cutlines are virtually invisible, based on the value you specify.

You set up how you want to blend the seams in the Set Blend Width window, which you can open from either the Mosaic Tool window or the Collection Viewer window.

  1. To set a blend width for all images right-click Source images header > Set Blend Width. To set the width for a specific image right-click the image > Set Blend Width

 

  1. In the Set Blend Width window, make sure the Use blend width check box is selected. Type the width value that you would like to use

5. Adjust Normalization

You can choose to apply normalization to all of the images, or individual images in the Source Images list. There are three different normalization methods that you can apply:

None – This does not apply any normalization

Hot Spot - A hot spot is a common distortion in aerial photographs and optical-satellite images. The distortion is caused by solar reflections, which often appear circular in photographs. Hot spot normalization removes distortion from aerial and optical-satellite images. It normalizes the brightness over the image by fitting a Gaussian surface to the brightness values. Hot spot normalization does not remove smaller spot reflections from lakes, cars, and buildings.

Adaptive Filter - Use Adaptive filter normalization with images that have a large, irregular bright-and-dark pattern that cannot be modeled to a Gaussian surface. Patterns that model to a Gaussian surface are better handled by Hot spot.  Adaptive filter normalization adjusts the brightness and contrast over local areas, thereby improving image detail, while reducing the bright-and-dark pattern over the entire image.

Note: Because of the intensive processing required, Adaptive filter normalization is not dynamic; that is, the display is not updated when you apply the command, but applied in the output mosaic. Also, any color-balancing effects in the normalized image are visible only in the output mosaic.

  1. To adjust the normalization on a single image: Right-click the image > Normalization > Choose Method.

    Example:

               Before Hot Spot Normalization                          After Hot Spot Normalization

     

  2. To adjust the normalization on all images: Right-click the Source Images header > Normalization > Choose Method.
  3. To adjust the normalization on more than one image: Select the images in the Source Images section and click the Normalize button on the toolbar .

6. Edit Colour Balancing

One of the key requirements with mosaicking is ensuring that the colors of adjacent images on either-side of a cutline are as similar as possible.

Color Balancing in Manual Mosaicking can be done in two ways: Manual Area or Overlap Area.

Manual Area: The Manual Area color balancing method is based on the match areas that you identify in the overlapping sections of the image. These match areas are used to compute a lookup table (LUT) that adjusts the color in the image that you are adding to match the images that will be mosaicked first.

Overlap Area: The Overlap Area color balancing method computes the color balancing histogram using only the pixels in the overlapping area of the images being added to the mosaic file.

NOTE: The strategy for collecting overlap areas will vary from image to image. If the input images are similar in appearance, you can collect a single match area in the overlapping area between two images to achieve a good color balance between the images. However, you can collect several match areas if desired. For example, you can collect small match areas representing the different areas so the lookup table can be used to accurately correct radiometric mismatches. Collect a match area in a green area to balance greens, a match area in a dark area to match dark values, a match area in urban areas to match urban areas, and so on. Using a single large match area covering a large part of the overlapping images tends to only be effective if you have an overall bright or dark difference between the images.

  1. To do a color balancing with Match Areas, select the image in the file tree and click on the New Match Area icon  to begin the color balancing process.
  2. Draw the match area(s) in the main or collection viewer. Collect small match areas representing the different areas so the look-up table can be used to accurately correct radiometric mismatches.

 

  1. To apply color balancing to the image, click on the Color Balancing icon pull down menu. Choose between the Manual Area and Overlap Area to perform color balancing. If you don’t have match areas for the selected image, this option will be disabled. If you are unsatisfied with the color balancing outcome, click on the Color Balancing pull down menu and click on None; or hit the ‘Undo’ button which will apply the previous color balancing outcome.

 

  1. Continue to apply colour balancing to the rest of the images.
  2. After the colour balancing step is completed and you are satisfied with the results displayed in the mosaic window, proceed to generating the mosaic.

7. Add Source Images to Mosaic

The final step in the mosaic creation process is to add the edited source images to the defined mosaic.

  1. To add all of the images from the Source Images list to the mosaic, right-click Source Images and click Add to Mosaic. At this time, the full mosaic will begin to generate. The images will be added to the mosaic file in the order that they appear in the Source Images list.

You can also choose to add individual images to the mosaic file by right-clicking the image in the Source Images list and selecting Add to Mosaic.

** Note – If Add to Mosaic is not available from this drop-down menu, the mosaic file may not yet be defined. You can right-click Output Mosaic and choose Define Output Mosaic. Define Output Mosaic is also available from the Tools menu. 

  1. Once the mosaic generation is complete, the images will be added to the mosaic and will no longer be available in the Source Images list.
  2. You can expand the mosaic file to check which images are added to the mosaic.

8. Restore Images to Source

After generating the mosaic file, you can choose to reprocess any of the images if you notice a problem in the mosaic.

  1. In the Output Mosaic section expand your mosaic file. You will see all of the images that comprise the mosaic.
  2. Right-click on the image that you wish to edit and click Restore to source
  3. Once the images are reloaded into the Source Images section you can edit them and add them back to the mosaic.

9. Additional Tools

The tools outlined in the section below are optional steps that could be taken with your mosaic. The tools shown below are particularly beneficial when working with larger mosaics that require quality control and verification from multiple users.

9.1 Quality Control Layer

Potential problems in the mosaic can be identified using the Quality Control layer along with reference vectors and the mosaic preview. These problems can be addressed before generating the final output mosaic.

  1. From the Mosaic Tool main menu, select: File > New Quality Control Layer. 

         Note: If the mosaic project already contains a Quality Control layer, this option is disabled.

  1. The new Quality Control layer appears in the Mosaic Tool's Control pane.

         

         The Quality Control toolbar opens automatically.

  1. To turn the Quality Control Layer on and off, clear the check mark besides Quality Control Layer in the Image Tree List.
  2. In the Mosaic Tool view pane, zoom to an area that you want to flag for quality control purposes.
  3. From the Quality Control toolbar, select Point New .
  4. Click to place the new point.
  5. You can then modify the Type and Comment for the point.

9.2 Verification

This tool is particularly useful with a larger mosaic. When you inspect the quality of your mosaic and, if necessary, modify any images, you can change the status of one or more. Typically, this is to change the status to Verified from the default Unverified. Assigning a status helps you keep track of images you have and have not modified. Images marked as Verified will appear in green.

  1. In the Mosaic Tool window, click the Map Layer Selection tool
  2. Select the image or images for which you want to change the status.
  3. Click the Image Status button arrow and select Verified or Unverified.

9.3 Mosaic Overview Window

  1. On the Mosaic Tool toolbar, click on the Mosaic Overview  button.  The Mosaic Overview window will open with all images selected
  2. In the Mosaic Overview window, on the Selection toolbar, you can click Select to define a new working area. Defining a working area is to select the images you want to display and modify in the Mosaic Tool window. The working area you define determines the extents in the Mosaic Tool window and all of the data from the images you select will be displayed.
  3. In the Mosaic Overview window, on the Selection toolbar, click Select, and then do one of the following:
    • Drag to select one or more images. Each image that intersects the rectangle you draw is selected.
    • To select an individual image, click the image you want. To select the next overlapping image, and thereby use its extents, at the same location, click again

The selected images are now locked for editing by you, and other users can neither select nor edit the images.

  1. After you select the images you want to modify, click Open Selection.

 

  1. The selected images are opened in the Mosaic Tool window based on the defined working area.

 

  1. You can then edit the selection that was loaded.
  2. Once the edits are complete you can mark the images that you edited as Verified. The images will also show up as verified in the Mosaic Overview window.

 

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