Tile Stitching

Sometimes Pix4d will output multispectral data into tiles. These tiles need to be stitched together and then overlaid to create a single layer showing the reflective multispectral data. This can be done using the gdal extension within QGIS software.

  1. Check your data. The tiles will be found in your pix4d data folder under 4_index > relfectance > tiles.
  • You will want to check that you have tif images for the correct bands. Also check there is the same number of tifs for each band.
  • Ensure that you have local copies on your computer and you are not looking at files in the drive. If you are then copy the tif files into a local folder. Image of tile directory
  1. Open up QGIS. Under Raster > Miscellaneous select Build Virtual Raster. For input files select all the tiles of a single band (ie red_1_1 to red_2_2_). Click Ok
  • Select the NoAlpha tiles and not the Transparent_Reflectance version.
  • For output, select the same folder as the input and title the VRT “Location-Date-Band-NoAlpha.vrt” Build Virtual Raster

You should have a notification that the process is complete and the stitched tifs should now appear as one layer on canvas. Repeat this process with every band

Multi-Band Stacking

This is for when you have all the tiles of one band together as one image. This process merges the reflective tile into one image with mutliple bands.

  1. At the top of the QGIS window under Raster > Miscellaneous select Merge
  • The input files should be the .vrt files you completed in the previous step
  • Output should be “location-date-MergedNoAlphaReflectance.tif” and should be in the same folder as the data.
  • Select each input file as a separate band Merging Bands
  1. Click the edit icon to the right of the command line window at the bottom of the prompt.

  • Replace the first line with the following text

    gdal_merge.bat -separate -of GTiFF -co COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9 -o

  • Make sure the bands are in the order if Blue (if applicable), Green, Red, Red Edge, NIR You can now run the command. It may take a few moments to process

  1. You should now have a multi colored reflective single raster image. It likely will look purple or blue but you can convert it to a false color composite and it should like the example below. This file should be uploaded to the main results folder for this flight. False Color Example Merged Reflectance