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Generate an orthomosaic using the Orthomosaic wizard

Available with Advanced license.

An orthomosaic is a georeferenced image product mosaicked from an image collection, where the geometric distortion has been corrected and orthorectified.

Seamlines and orthomosaic

The Orthomosaic wizard provides a common workflow for generating ortho image mosaics from the adjusted image collection. The Orthomosaic wizard provides a guided workflow with three preconfigured steps to generate a photogrammetrically corrected image from your image collection:

  1. Seamline generation
  2. Color balancing
  3. Orthomosaic settings

You can modify the default processing parameters, but you cannot remove a step. If you want to perform a specific step, you can use the Custom wizard.

Seamline Settings page

The first page to create a mosaic is to specify the seamline settings. Seamlines are polygons that are used for defining mosaicking boundaries and resolving the image overlaps.

Parameters for Seamline Settings

Parameter nameDescription

Select Mosaic Candidates

The Select Mosaic Candidates parameter is normally used for image collection with dense overlaps such as drones. It is used to find an optimum set of images that can be used in mosaicking images. The selected images will be used in seamline building, color balancing, and output mosaic operation.

Check on the checkbox to perform the selection of the best image candidates to use.

Maximum Overlap Area

The maximum amount of overlap that you want between the mosaic dataset and the footprint of each image in the mosaic dataset. If the percentage of overlap is higher than this threshold, the image is excluded since it will have too much redundant information.

The percentage is expressed as a decimal. For example, a maximum overlap of 60 percent is expressed as 0.6.

Maximum Area Loss Allowed

This is the maximum percentage of area that can be excluded by the candidate images. After the tool chooses the best candidate images based on the Maximum Area Overlap, it will then check to see if the maximum excluded area is below the threshold specified. If the excluded area is greater than the specified threshold, the tool will add more candidate images to fill in some of the voids that were missing. Most of these excluded areas will likely be along the border of the mosaic dataset.

The percentage is expressed as a decimal. For example, a maximum excluded area of 5 percent is expressed as 0.05.

Computation Method

Choose the computation method to use to generate your seamlines:

  • Geometry—Generate seamlines for overlapping areas based on the intersection of footprints. Areas with no overlapping imagery will merge the footprints.
  • Radiometry—Generate seamlines based on the spectral patterns of features within the imagery.
  • Edge Detection—Generate seamlines over intersecting areas based on the edges of features in the area.
  • Voronoi—Generate seamlines using the area Voronoi diagram.
  • Disparity—Generate seamlines based on the disparity images of stereo pairs. This method can avoid seamlines cutting through buildings.

Cellsize

Generate seamlines for raster datasets that fall within the following range of spatial resolutions.

Minimum Region Size

Specify the minimum region size, in pixel units. Any polygons smaller than this specified threshold will be removed in the seamline result. The default is 100 pixels.

Blend Width Units

Specify the unit of measurement for blend width.

  • Pixels—Measure using the number of pixels. This is the default.
  • Ground units—Measure using the same units as the mosaic dataset.

Blend Width

Blending (feathering) occurs along a seamline between pixels where there are overlapping rasters. The blend width defines how many pixels will be blended.

If the blend width value is 10, and you use BOTH as the blend type, then 5 pixels will be blended on the inside and outside of the seamline. If the value is 10, and the blend type is INSIDE, then 10 pixels will be blended on the inside of the seamline.

Blend Type

Determine how to blend one image into another, over the seamlines. Options are to blend inside the seamlines, outside the seamlines, or both inside and outside.

  • Both— Blend using pixels on either side of the seamlines. For example, if the Blend Width is 10 pixels, then five pixels will be blended on the inside and outside of the seamline. This is the default.
  • Inside—Blend inside of the seamline.
  • Outside—Blend outside of the seamline.

Request Size Type

Set the units for the Request Size.

  • Pixels—Modify the request size based on the pixel size. This is the default option, which resamples the closest image based on the raster pixel size.
  • Pixel scaling factor—Modify the request size by specifying a scaling factor. This option resamples the closest image by multiplying the raster pixel size (from cell size level table) with the pixel size factor.

Request Size

Specify the number of columns and rows for resampling. The maximum value is 5,000. Increase or decrease this value based on the complexity of your raster data. Greater image resolution provides more detail in the raster dataset but also increases the processing time.

Minimum Thinness Ratio

Define how thin a polygon can be, before it is considered a sliver. This is based on a scale from 0 to 1.0, where a value of 0.0 represents a polygon that is almost a straight line, and a value of 1.0 represents a polygon that is a circle.

Slivers are removed when building seamlines.

Maximum Sliver Size

Specify the maximum size a polygon can be to still be considered a sliver. This parameter is specified in pixels and is based on the Request Size, not the spatial resolution of the source raster. Any polygon that is less than the square of this value is considered a sliver. Slivers are removed when building seamlines.

Color Balance Settings page

The second page covers color balancing your mosaic. Color balancing makes transitions from one image to an adjoining image appear seamless.

Parameters for Color Balance Settings

Parameter nameDescription

Balance Method

The color balancing algorithm to use.

  • Dodging—Change each pixel's value toward a target color. With this technique, you must also choose the type of target color surface, which affects the target color. Dodging tends to give the best result in most cases.
  • Histogram—Change each pixel's value according to its relationship with a target histogram. The target histogram can be derived from all of the rasters or you can specify a raster. This technique works well when all of the rasters have a similar histogram.
  • Standard deviation—Change each of the pixel's values according to its relationship with the histogram of the target raster, within one standard deviation. The standard deviation can be calculated from all of the rasters in the mosaic dataset or you can specify a target raster. This technique works best when all of the rasters have normal distributions.

Color Surface Type

When using the Dodging balance method, each pixel needs a target color, which is determined by the surface type.

  • Single color—Use when there are only a small number of raster datasets and a few different types of ground objects. If there are too many raster datasets or there are too many types of ground surfaces, the output color may become blurred. All the pixels are altered toward a single color point—the average of all pixels.
  • Color grid— Use when you have a large number of raster datasets, or areas with a large number of diverse ground objects. Pixels are altered toward multiple target colors, which are distributed across the mosaic dataset.
  • First order— This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All pixels are altered toward many points obtained from the two-dimensional polynomial slanted plane.
  • Second order— This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All input pixels are altered toward a set of multiple points obtained from the two-dimensional polynomial parabolic surface.
  • Third order— This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All input pixels are altered toward multiple points obtained from the cubic surface.

Target Raster

The raster you want to use to color balance the other images. The balance method and color surface type, if applicable, will be derived from this image.

Recalculate Statistics

Once color balancing has been performed, there may be new pixel values within your raster. Check the checkbox to calculate the statistics with latest pixel values.

Orthomosaic Settings

The third page covers the output settings for your mosaic.

Parameters for Orthomosaic Settings

Parameter nameDescription

Pixel Size

The pixel size for the output orthomosaic.

The output pixel size should be the same or larger than the pixel size of source image.

Format

The output format for the output orthomosaic.

  • Cloud Raster Format
  • TIFF Format
  • JPEG Format
  • JPEG2000 Format
  • Meta Raster Format

Compression

The compression method for the output

  • None
  • LZW
  • JPEG
  • LERC
  • JPEG2000

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