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How to mosaicing multiple orthophotos

This article shows you how to create and upload a mosaic of orthophotos in your eVouala account. Be sure to have on your computer GDAL/OGR software to process raster files.  For the purpose of this exercise, we will download a set of two orthophotos from Township Of Langley (in Canada) open data portal. A real use case you will have much more the only two Orthophotos.


Next step will be to compress and add an overview of all your raster files. For this use gdal_translate and gdaladdo command line tool: (read this article for more information about this tool)

gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES 526E_5443N.tif 526E_5443N-3857-ycbcr.tif
gdaladdo --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config INTERLEAVE_OVERVIEW PIXEL -r average 526E_5443N-3857-ycbcr.tif 2 4 8 16
gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES 527E_5443N.tif 527E_5443N-3857-ycbcr.tif
gdaladdo --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config INTERLEAVE_OVERVIEW PIXEL -r average 527E_5443N-3857-ycbcr.tif 2 4 8 16

The last step will be to create a VRT file. This will allows you to "virtually" merge all raster files together.  Again, for this step you also use a GDAL/OGR tool that will let use create a VRT file:

gdalbuildvrt TownshipOfLangley.vrt *r.tif

tol.png

Now to test the result of your work, open QGIS and drag-and-drop the VRT file from your file browser in QGIS layer tree.  You will see how fast the navigation will be!  To visualize your mosaic in eVouala, you will need to zip the compressed tif files with the VRT file (very important) and drag-and-drop it on import view.

import.png

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