Use the comparison tools to conduct visual analysis and find differences in imagery to complete an image-based task. The comparison tools contain features to highlight areas of interest through layer comparison and change detection.
Use the Swipe tool
The Swipe tool allows you to interactively compare two layers vertically or horizontally in the Map Panel. This allows you to see what is underneath the layer you are focused on while analyzing imagery.
The Primary and Comparison layer drop-down menus will always contain the image layers but will also display images that you selected from the metadata table. Only two layers can be compared at a time. The web map is not available as a Comparison layer and is only available as an option for a Primary layer.
To use Swipe, complete the following steps:
- Click Tools
in an open project. - Click Swipe under Comparison Tools.
- Select a Primary layer.
- Select a Comparison layer.
Note:
The basemap is not available as a comparison layer. If additional layers are added through Add Layer, Web Map, or returned as a result from running another tool, use Refresh Layers
to refresh and update the list of layers available in the tool. - Choose Vertical or Horizonal for the swipe bar direction.
Note:
The default swipe direction is Vertical. - Click Apply.
The primary and comparison layer names will be added as a label in the Map Panel to provide context as to which image is displaying.
- Use the Swipe tool controls in the Map Panel header to change the swipe direction or to reset the tool and start again.
Note:
If the Map Panel is not visible, the Swipe tool is unavailable.
Use the Flicker tool
The Flicker tool is used to visually compare images. The Flicker tool allows you to display multiple layers underneath other layers by quickly turning it on and off automatically based on a defined rate. This can be useful for temporal change detection, data quality comparison, and other analysis you want to see between layers.
The Flicker tool is accessed from the Tools menu under Comparison Tools. The Map Panel must be visible to use the Flicker tool. The Web Map and Image Layer options are always available to you. The images you select from the metadata table are the images that will appear in the drop-down menu to apply to the Flicker tool.
The default and minimum flicker interval rate is half of a second (500 ms), while the maximum rate is five seconds (5000 ms). To use the Flicker tool:
- Click Tools in an open project.
- Click Flicker under Comparison Tools.
- Select at least two layers to be applied to the tool.
If additional layers are added through Add Layer, Web Map, or returned as a result from running another tool, use Refresh Layers
to refresh and update the list of layers available in the tool. - You can use the Move Up or Move Down buttons to set the order of how the images will be displayed when they are played.
- Click Apply.
- Slide Rate to choose a flicker rate between 0.5 seconds and 5.0 seconds.
- Click Play
.As the tool plays, the active layer name will be added as a label in the map panel to provide context as to which image is displaying.
The imagery layers are locked once Play
is clicked. - Use the Flicker tool controls in the map header panel to play or pause the tool, jump to the start or end of the images, or to reset the tool if you want to use another tool at the same time as the Flicker tool.
- Click Pause
to halt the Flicker tool or to choose new images to compare. - Click Reset
to return to the default settings of the tool.
Use the Detect Change tool
The Detect Change tool conducts automated pixel-based comparisons between two images selected in the image metadata table. This tool detects image change using multiple raster functions.
The tool must be run against two different raster IDs from a single image service that is query and search enabled. Once these images are selected, you can define the area of interest that the tool will run against. Results are returned as in-memory graphics that you can use for immediate visual comparison or in Excalibur project reports.
To use the Detect Change tool, complete the following steps:
- Click Tools in an open project.
- Click Detect Change under Comparison Tools.
- Click Image Metadata to expand the table.
- Check the boxes for two images in the table.
- Click the down arrow to collapse the Image Metadata table.
- Choose an image for Input Image 1.
If no images are selected in the image metadata table, a message will show in the view.
- Choose an image for Input Image 2.
You cannot choose the same image as Input Image 1.
- Click Draw Area
to draw a rectangle to define an area of interest.Alternatively, click Clear
to redraw the area of interest.An error will display If the area of interest is drawn outside of the selected image extent.
- Optionally, adjust theTransparency of the detection between 0% and 100%.
- Optionally, change the Threshold between Lower and Higher.
A lower threshold will find more differences in pixels between the images, but could add unwanted noise in the results. A higher threshold will return fewer pixels, but could exclude important changes. You may need to try a few different settings in different runs of the tool to see what will work best for the selected input rasters and the expectations for the results.
- Optionally, click Change Color to change the color of your detection when it appears.
- Click Submit.
Results are dynamically returned as graphics on the image.
- Click Reset to clear the results, selected images, and the drawn area of interest.
Note:
The tool is unavailable if the active image service is non-query enabled or not an ArcGIS imagery layer. If there is only one image in the image metadata table, the tool will also be unavailable as a minimum of two selected images is required to run the tool.
Use the Compute Change tool
The Compute Change tool computes the difference between two raster datasets. It can be leveraged to enumerate the differences between two classified rasters for land-coverage change analysis, or to examine changes between two single-band, continuous rasters such as elevation, temperature, canopy cover, and more. An output raster is generated, showing the difference between the two datasets.
To use Compute Change, complete the following steps:
- Click Tools in an open project.
- Click Compute Change under Comparison Tools.
- Select a Primary layer to be the basis for comparison.
The project must have two different images that can be selected. They can be selected from layers added to the project web map, or from images selected in the Image Metadata table.
- Select a Comparison layer.
- Select Use the view extent or Draw an area to define the Area of Interest. For Use the view extent, pan and zoom in the Map Panel to the desired area. For Draw an area, click Draw Area and draw the desired extent in the Map Panel.
Once enabled, click Cancel
to cancel the drawing. - Click Continue. Alternatively, click Reset to clear the selected images and srea of interest.
- Choose a calculation Method under Properties.
- Difference—The mathematical difference, or subtraction, between the pixel values in the Primary layer and the pixel values in the Comparison layer.
Comparison layer - Primary layer - Relative Difference—The difference in pixel values accounting for the quantities of the values being compared.
(Comparison layer - Primary layer)/max(Primary layer, Comparison layer) - Spectral Euclidean Distance—The Euclidean distance between two multiband rasters, where each pixel is treated as a vector. Larger values indicate more change between the images.
- Spectral Angle Difference—The spectral angle between two multiband rasters, where each pixel is treated as a vector. Larger angles indicate more change between the images.
- Band With Most Change—The band that accounts for the most change in each pixel between two multiband rasters.
- Difference—The mathematical difference, or subtraction, between the pixel values in the Primary layer and the pixel values in the Comparison layer.
- Type a Layer Name for the output layer.
- Optionally, change the output Folder to a different folder, or create a new one.
- Click Run. Alternatively, click Reset to reset the tool parameters.
The results will appear in the canvas and in the Layers list when the tool completes successfully. Any errors in the process will be returned by the server and displayed in the tool.