If you have processed your dataset using the Propeller platform you can download a high resolution orthomosaic in GeoTIFF format in your sites coordinate system. If the GeoTIFF file size is too large to use with your software, you can use QGIS to compress the file.
As a prerequisite you will need to have QGIS installed on your computer. If you don't have it, follow these instructions. Before you start the compression process you need to load your GeoTIFF into QGIS by either dragging and dropping onto QGIS or use the Add Raster Layer function from Layer menu.
You can compress GeoTIFFs using QGIS in 3 different ways. We have recorded them below for your reference.
- An orthomosaic in the GeoTIFF file format
- QGIS installed on your computer
1. Exporting the file and re-scaling the pixel size
This is the easiest method where you just need to export the original GeoTIFF with bigger pixel size. This will allow you to save some space on your computer. However, the output file will have a reduced resolution where you may lose some details.
2. Aligning the file with the Lanczos algorithm and re-scaling the pixel size
Aligning the raster is a very similar method to the exporting one, however, it can use different algorithms to re-sample the pixel size. The Lanczos algorithm gives the best results and you will not lose as much of the original photo quality.
3. Compressing the file with JPEG compression (recommended)
The last method is the actual compression. It uses JPEG compression but the output file will remain a GeoTIFF. As you don't change the size of the pixel you are not losing the resolution and accuracy quality, which in our opinion makes this method the best choice from the available ones.
The below table presents how the size of the input file changes over Aligning raster and JPEG compression:
You should also be aware of the downsides of the compression in QGIS:
- Change of the pixel size while exporting or aligning raster - the spatial resolution of the output file is changed so the file may not be the high resolution file anymore and as a result you may loose some of the information or details.
- Time consuming - depending on the original size of the file sometimes it can take up to 1-2 hours to compress the input file.
- Some third-party software may not be able to open tiled or BigTIFF files - while creating output files with JPEG compression we choose these parameters, you should be aware of the limitations that some software may have.
I still can't do it!
We wrote these articles to arm you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient. If you're stuck, you can connect with our support team by clicking the support button on the top right corner of your user portal.