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Projections, datums, and coordinate systems
Projections, datums, and coordinate systems

Background on spatial referencing and how to convert projections and coordinate systems

Karen Joyce avatar
Written by Karen Joyce
Updated over a week ago

When you upload drone mapping images to GeoNadir, each photo is tagged with the latitude and longitude of drone location at the time of capture. When we process these data to create the orthomosaic, DSM, and DTM, the data are projected onto the surface of the earth and assigned with the WGS84 datum and Transverse Mercator projection.

The combination of WGS84 and Transverse Mercator works well on a global scale. This is important for consistency across GeoNadir as we are a global platform.

However in some cases, you may wish to use a projection or datum that is optimized to reduce distortions in your local area. This will give you the most accurate distance and area measurements at your site.

To convert your processed products to a local datum and projection, you will need to download the products and have access to GIS or image processing software (e.g. QGIS, ArcGIS Pro, ENVI). Then you will be able to follow these steps:

  1. Download the orthomosaic, DSM, and DTM (Professional and Pro + subscriptions only)

  2. Open the files in your GIS or image processing software

  3. Search for the reproject tool

  4. Select your desired output datum, projection, coordinate system (your input should be auto-detected as WGS84 and UTM zone XX where XX is the UTM zone in the location of your dataset)

  5. Apply the reprojection tool. This will generate a new file so make sure you name it appropriately.

Do not attempt to just modify the metadata to read your desired datum and projection. This will result in all sorts of positional errors. You must use a reprojection tool to apply the mathematical algorithm to transform the data itself.

Note that you no longer need to reproject your data to overlay datasets with different projections and coordinate systems. Most GIS and image processing packages are able to read the file metadata and perform overlay corrections on the fly.

Further help on finding and applying the tool to reproject your data:

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