Create a DSM/DEM for SkySat imagery workflow

Introduction

Sharing instructions and examples of how to include DEM in satellite images packages

Instructions

DEM generation from (SkySat) stereo steps are usually platform or software specific.

 

Please see this article on a sample workflow and detailed implementation of DEM on SkySat imagery: https://www.sciencedirect.com/science/article/pii/S0924271620303506

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 This is an example of how it can be used in ArcGIS Pro 2.8 (or higher):

Elevation data can be derived from stereo image pairs using photogrammetry algorithms. A stereo pair is comprised of two images of the same geolocation taken from different perspectives.

Stereo image pairs collected from different perspectives

The stereo image pairs of an image collection are used to generate a point cloud (3D points) from which elevation data can be derived. The derived elevation data will be used to orthorectify the image collection in the ortho mapping workspace.

For more detailed information please visit this site:
https://pro.arcgis.com/en/pro-app/help/data/imagery/generate-elevation-data-using-the-dems-wizard.htm
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ENVI, L3 Harris Geospatial, has an add-on that you can use too. 

There are three steps in creating a DEM that are crucial to generating acceptable results: epipolar image creation, image matching, and DEM geocoding.

  • Epipolar Image Creation: Creating epipolar images is an essential processing step in DEM extraction. Epipolar geometry describes the geometrical constraint between two frame images of a stereo pair. It represents the fact that a ground point and the two optical centers lie on the same plane. This means that for a given point in one image, its conjugate point in the other image must lie on a known line in the second image. By creating epipolar images, the search space for finding corresponding image points in automatic image matching is reduced. For information about building epipolar images for the use with DEM Extraction Wizard, see Generate Epipolar Images.
  • Image Matching: Image matching finds the conjugate points on both the left and right images which correspond to the same ground feature. The output of the image matching procedure is called a parallax image, in which the x-coordinate difference (along epipolar lines) between the left and right image is stored and is used to build the DEM. Thus, the quality of image matching largely determines the quality of the output DEM.
  • DEM Geocoding: DEM geocoding reprojects the DEM from the epipolar projection to an output map projection and units that you specify. This step involves filling failed pixels and resampling to a pixel spacing that you specify. When you provide ground control points (GCPs), you can compute the absolute orientation of the computed terrain model in this step.

For more information on using the ENVI add-on please see the link below:
https://www.harrisgeospatial.com/docs/IntroductionToDEMExtraction.html

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