25Apr
Published On: 25 April 2019

Elevation Problems Resolved with Geoid Model Support in delair.ai

Finally, a drone data processing platform that supports more than just ellipsoid heights and fixed elevation offsets! You can now use your vertical coordinate reference system or datum of choice, such as NAVD88 in the US, through the support of geoid models in delair.ai.

A big challenge that a lot of drone surveyors face during the photogrammetry process is getting the final georeferenced map products to align properly with their or their clients’ existing geospatial data.  This is not because the data are bad, but often because there has been either an incorrect datum transformation, a projection error, or simply because the drone data has not been transformed to match the source data.  The elevations can be the hardest to troubleshoot because the map looks fine, but when you hand the point cloud or a surface model to an engineer who compares it to existing data, there is a consistent (or worse, a very inconsistent) vertical shift across the entire dataset.  More often than not, this is due to a user error in the data processing parameters, a lack of local geoid model support in the chosen photogrammetry software, or a less-than-adequate transformation protocol being applied to the final deliverables after the photogrammetry process, which introduces new sources of error.

The delair.ai platform makes this problem easy to avoid by taking care of it at the very beginning of the process.  The most common professional mapping drones record the photo center coordinates in the exif data in WGS84 latitude/longitude for the horizontal, and either ellipsoid or EGM96 height in meters for the vertical. When you import these photos into the delair.ai platform, the WGS84 latitude/longitude coordinates are automatically read, then you indicate whether the elevations are in ellipsoid height or according to a certain geoid model (such as EGM96).

Next, you select the coordinate reference system (CRS) in which you want to process your data and ultimately export any layers.  This is where delair.ai makes surveyors happy. You can select your preferred projected CRS of choice from a library by searching for the EPSG code or by keyword.

Then finally, you can set the vertical CRS to either the ellipsoid height of the selected horizontal CRS, or to any one of multiple local geoid models supported and maintained by the delair.ai platform. Currently this includes many geoids for North America and Europe, and more regions will be added based on customer demand.

For example, if you are doing a topographic survey in near Boise, Idaho, USA, you can set your CRS to the state standard of US State Planes NAD83, Idaho West zone, in US survey feet (EPSG code 2243) and set the vertical CRS to use GEOID12B in order to adhere to the NAVD88 datum.

While the Delair Aerial Intelligence platform is often looked to for the advance business analytics it provides for mines, quarries, construction, agriculture, and other markets, it is important to highlight that the core functions of the platform are designed to support the workflows and high-accuracy data products that land surveyors require. Coupled with a Delair UX11 UAV with PPK, you can expect to end up with accurate maps in the coordinate system you require.