[Proj] Data-driven projections Re: Understanding 2D Helmert

[Kristian Evers]

Luke,

It is an interesting idea you and your colleague are bringing to the table here. I can certainly see why it is intriguing to have data-driven projections readily available in GIS applications. I am not entirely convinced that PROJ is the right tool for the job though. I can easily see PROJ implement various generic mappings consisting of an arbitrary set of parameters [0], where it would be up to the user of PROJ to submit the needed parameters. Similarly to how various projection parameters are in the hands of the user already.

The paper doesn’t go into much details with the math behind the mappings, nor how the mapping between geodetic coordinates and projected coordinates stated in the mapstring should be determined (it seems like there is a chicken and egg type of problem here). For me to really be able make a judgement if this is suitable for PROJ I need some elaboration on those points.

/Kristian

[0] PROJ’s Horner transformation is an example of one such mapping (https://proj4.org/operations/transformations/horner.html?highlight=horner)

On 28 Oct 2018, at 19:54, Luke Bergmann <luke.bergmann at gmail.com<mailto:luke.bergmann at gmail.com>> wrote:



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