[PROJ] Determine "cut line" for arbitrary projection

[Lesparre, Jochem]

> The basic idea is to densify the vertices in areas with high distortion and possibly removing ones in areas with low distortion. For visualisation purposes I think this is neat solution but it may not be desirable in a GIS where you want the user to have full control over the vertices in a geometry.

Indeed. There is difference between the data vertices and how the data should be visualised. I think edges shouldn't be visualised with straight edges between vertices, but with geodesics. This means intermediate points (for visualisation only) are needed. As long as not all GIS software is visualising edges as geodesics, I recommend Dutch data creators to add intermediate points themselves. For common projections like ETRS89-LCC, LAEA, UTM etc., I analysed the required line segment length between intermediate points. For Europe the worst cases for common projections are World Mercator and Web Mercator. I made a graph for the relation between line segment length and deviation between a straight line and the geodesic for these projections:
https://www.euref.eu/sites/default/files/symposia/2024Barcelona/15-01-Lesparre.pdf (slide 12) which shows for example: for 1 cm accuracy, the vertices should not more than 400 m apart in North Scandinavia and not more than 1000 m apart in the South Mediterranean.

Jochem



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