Co-registration with SNAP

Visualize geometric offset

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

\geodata\uas\clip_ebee_ortho_align.tif is a reference image which is very well georeferenced. \geodata\uas\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.

• 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:

• 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

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)

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