GPSBabel: convert, manipulate, and transfer data from GPS programs or GPS receivers. Open Source and supported on MacOS, Windows, Linux, and more. Pointy clicky GUI or a command line version...
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[Gpsbabel-misc] Accuracy of BNG > GPX (WGS84) transformation
Mon, 5 Aug 2024 19:37:42 +0200
Previously we used the Molodensky transform. This PR adds an implementation of the Helmert transform, and uses it to transform between OSGB36 and WGS84. Transforms between other coordinate systems still use Molodensky. Using the Helmert transform for other use cases would require knowledge of the translation, rotation and scaling parameters between those coordinate systems.
This came up on: [Gpsbabel-misc] Accuracy of BNG > GPX (WGS84) transformation Mon, 5 Aug 2024 19:37:42 +0200
Previously we used the Molodensky transform. This PR adds an implementation of the Helmert transform, and uses it to transform between OSGB36 and WGS84. Transforms between other coordinate systems still use Molodensky. Using the Helmert transform for other use cases would require knowledge of the translation, rotation and scaling parameters between those coordinate systems.
https://www.ordnancesurvey.co.uk/documents/resources/guide-coordinate-systems-great-britain.pdf states that we should expect errors up to 3.5m with the Helmert transform.
This does NOT implement OSTN15. If you really need better accuracy then you should convert your coordinates outside of GPSBabel.