Seamlines are used when mosaicking images in a mosaic dataset. Use seamlines instead of footprints to define the edges along which the images in the mosaic dataset are mosaicked together. A mosaic dataset using seamlines removes overlap between the images in the mosaic dataset. The Seamlines mosaic method is recommended when you do not need to view individual mosaic dataset images separately, or when you want to keep specific features from one input image visible throughout the mosaic dataset. For example, if tall buildings are visible in your mosaic dataset, you may want to see the building from only one perspective and prevent it from appearing disjointed or split as you pan the mosaic dataset.
When you use the Seamline mosaic method, the mosaicked image does not change as you move around the image, as can happen when using other mosaic methods, such as Closest To Center. Also, when you create seamlines, you can ensure that the mosaicked image is optimally displayed by editing the seamlines so features do not appear disjointed.
Seamline creation
To create seamlines for a mosaic dataset, use the Build Seamlines tool. Seamlines are similar to footprints: there is one polygon representing each image. The shape of the polygon represents the part of the image that is used to generate the mosaicked image when viewing the mosaic dataset. Once the seamlines are built, a Seamline layer is present in the Contents pane each time you add the mosaic dataset to ArcGIS AllSource.
By default, the seamlines are generated using the North-West mosaic method. You can also create the seamlines using the Closest To Viewpoint or By Attribute mosaic method. Based on the method, a ranking value is stored in the SOrder field in the attribute table. When the Seamline mosaic method is used, the SOrder field value is used instead of the ZOrder field value. The SOrder field value determines the order in which the images will be mosaicked together, and—as with the ZOrder field value—the lower value is mosaicked on top. The following example shows the mosaic order of three images and the area of overlap where the seamline will intersect:
You have several options when building seamlines:
- GEOMETRY—Create seamlines from the footprints without computing a path between intersecting points, but considering the mosaic method, such as North-West.
- RADIOMETRY—Build seamlines by examining the values and patterns in the intersecting area and compute a path between the intersecting points. This path is then merged with the footprint to create the seamline for each single image in the mosaic dataset. The diagram below
represents a series of seamlines created for 12 images. The mosaicking order uses the North-West method and the RADIOMETRY computation option.
- COPY_FOOTPRINT—Build seamlines by copying the footprints in which each seamline is the copy of the corresponding footprint.
- COPY_TO_SIBLING—Commonly used with satellite imagery when the panchromatic band does not always share the same extent as the multispectral band. This option ensures that they share the same seamline.
- EDGE DETECTION—Generate seamlines over intersecting areas based on the edges of the features in the overlap area. Use this option when you want to use the edge of the feature to make the transition less apparent.
- VORONOI—Incorporate the polygons in a Voronoi diagram to create the seamlines.
- DISPARITY—Create seamlines based on the disparity between images of stereo pairs. This option avoids splitting features between stereo images that may lean in different directions.
Use custom seamlines
If you have a seamline (polygon) file, first run the Build Seamline tool to establish the framework for the seamlines using the COPY_FOOTPRINT computation option. You can then use the Import Mosaic Dataset Geometry tool to replace the seamlines with your own.
Generate seamlines at different dataset levels
If the mosaic dataset is composed of multiple resolutions of data, such as high-resolution aerial orthoimagery and lower-resolution satellite imagery, you can generate seamlines that are unique to each of these datasets by specifying an appropriate pixel size. If you don't specify a pixel size, the seamlines are automatically generated for each pixel size specified in the pixel size level table of the mosaic dataset.
Blend along seamlines
You can define a blending value (feathering) and type that will occur along the seamline. Blending occurs between pixels in overlapping images. By default, the Blend Width value is defined in the mosaic dataset's default properties. This value defines the blending distance in pixels along the seamline. You can replace this value in the seamline attribute table.
The seamline attribute table contains a Blend Width field and Blend Type field for every seamline in the mosaic dataset. The options for the Blend Type field value are Both, Inside, and Outside. If the Blend Width field value is 10, and you use Both as the blend type, 5 pixels are blended on the inside and outside of the seamline. If the value is 10, and the blend type is Inside, 10 pixels are blended on the inside of the seamline. You can replace the Blend Type field value in the seamline attribute table.
To blend the pixel values along a seamline, you must set the mosaic method to Seamline and the mosaic operator to Blend. You can specify these settings in the Build Seamlines tool, or set them as default properties of the mosaic dataset.
Remove seamlines
To remove all the seamlines from a mosaic dataset, right-click the mosaic dataset in the Catalog pane and click Remove > Remove Seamlines.