Co-registration with SNAP

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Visualize geometric offset

  • Start SNAP Desktop
  • File --> Open Product.... Browse for Unmanned Aerial System (UAS) ortho mosaics:

clip_ebee_ortho_align.tif is a reference image which is very well georeferenced. clip_mavic_ortho_align.tif is an image with a positional offset. It needs to be registered to the reference image. Open or drag and drop marked files from Windows File Explorer into the SNAP Product Explorer tab.

  • Mark the reference image clip_ebee_ortho_align.tif in ToC. Right click Open RGB Image Window --> OK.
  • Mark the image to be registered clip_mavic_ortho_align.tif in ToC. Right click Open RGB Image Window --> OK.
  • Window --> Tile Vertically. Both side-by-side windows are spatially linked. Zoom in and use the Panning tool to see the offset between both images

Split multiband to single band files

  • Mark the image to be registered clip_mavic_ortho_align.tif in ToC. Raster --> Subset --> Band Subset. Check exclusivly band_1.

Snap specify band subset band 1.png

  • Repeat this step for band_2 and band_3 creating separated single bands of the image to be registered .

Co-registration of single band raster files

  • Raster --> Geometric operations --> GeFolki Co-registration.
  • Define I/O Parameters and Processing Parameters:

Snap gefolki io.png Snap gefolki params.png

  • Click Run.
  • Repeat this step for band_2 (subset_1) and band_3 (subset_2). Adjust processing parameters for each band, accordingly.

Stack single bands to multiband file

  • Create a stack of all coregistered single bands. Raster --> Geometric --> Collocation
  • Resampling Method: Bilinear Resampling

Snap collocation.png

Convert data type from float32 to uint8

  • Raster --> Data Conversion --> Convert Datatype
  • Check Save as and select GeoTIFF from drop downlist.
  • Target Data type: uint8
  • Scaling: Linear (slope and intercept)

Snap datatype io.png Snap datatype params.png

  • Mark the coregistered image collocate_cnv in ToC. Right click Open RGB Image Window --> OK. Check the geometric quality of the co-registration comparing the reference image clip_ebee_ortho_align.tif (bottom), the image with an positional offset clip_mavic_ortho_align.tif (middle) and the co-registered image collocate_cnv.tif (top).

Check collocation.png

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