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How we handle coordinate systems, GCPs, and geoids in Birdi

Kayley Greenland avatar
Written by Kayley Greenland
Updated over a week ago

Overview: This article explains how Birdi handles coordinate reference systems (CRS), ground control points (GCPs), and geoid height models during data import and processing.

1. Coordinate System Transformation During Processing

When a map is processed on the Birdi platform, you are required to set an export CRS. Both drone images (usually in WGS84/lat-long) and GCPs (typically in a projected CRS like easting/northing) are transformed into this target CRS.

  • All outputs are produced in the selected export CRS.

  • For web viewing, Birdi creates tiled outputs (e.g. COG rasters or Cesium 3D Tiles) in display-friendly CRSs such as EPSG:3857 (Pseudo-Mercator).

2. Viewing the CRS of Imported and Processed Files

You can view the CRS directly in the Birdi platform:

  • Navigate to the Layer Details tab.

  • CRS metadata is shown for:

    • Most imported rasters

    • Most imported vectors

    • All processed outputs

3. How Birdi Auto-Detects CRS

Birdi automatically detects coordinate systems where possible. Here's how it works by file type:

  • GCPs: CRS must be explicitly indicated at import.

  • Rasters: CRS is typically embedded in the metadata.

  • Vectors: CRS is either embedded or read from the accompanying .prj file.

  • 3D Cesium Tiles: Usually supplied in WGS84 (EPSG:4326).

4. Geoid Height Model Support

Birdi supports the use of geoid models to provide accurate vertical datum transformations. Supported geoids currently include:

  • au_ga_AUSGeoid09_V1.01.tif

  • au_ga_AUSGeoid2020_20170908.tif

  • egm96-15.tif

  • us_nga_egm2008_1.tif

  • us_nga_egm84_30.tif

  • us_nga_egm96_15

Need a different geoid? Reach out to Birdi support—we can extend the list upon request.

5. Selecting a Geoid for Processing

During processing, Birdi allows users to select coordinate systems that are either:

  • Geoid-based (e.g., AHD in Australia)

  • Ellipsoidal (e.g., WGS84 without geoid adjustment)

The CRS selector typically includes options with labels like "+AHD" to indicate geoid integration.

Need Help? If you're unsure about the correct CRS or geoid for your dataset, contact our support team with your EPSG code, .prj file, or geoid preference

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