[Proj] Conic projection, but centric (gnomonic)

[stevejking]

Lukasz Komsta wrote
> The closest solution is
> 
> +proj=eqdc +lat_1=52 +lat_2=52 +lat_0=52 +lon_0=19 +axis=esu +a=6390000
> +b=6390000 +ellps=sphere +x_0=330000 +y_0=-350000

Lukasz, if you are trying to transform from this projection to wgs84 or GPS,
you will need to add a +towgs84 or +nadgrids component. I think developing a
nadgrids gridshift file to accompany this would be the best solution, since
that could give the greatest accuracy since it can take account of the
apparent distortions in the original grid (as one of your links indicated),
as well as accommodate the main ellipsoidal latitude and longitude shifts
from your sphere to wgs84.

Steve 


Lukasz Komsta wrote
> Dear All,
> 
> In late 1970s, Institute of Botany of Jagiellonian University in Krakow
> (Poland) developed a geobotanical grid. This grid has interesting history,
> because the details of projection were never officially published. After
> my reverse engineering followed by further numerical investigation by my
> colleague it was revealed that this grid is based on something which is
> called in mapproj package "central conic projection" with one tangent
> (with quite strange Earth radius, but it is only a detail). The projection
> is from Earth center, not parallel nor stereographic.
> 
> I implemented this grid in various languages and the detailed info is
> here: https://atpol.sourceforge.io/.
> 
> The creators of original grid officially confirmed that this projection is
> same with their original idea and this caused rising of interest in usage.
> 
> However, there is no possibility to set this projection in PROJ4 (as far
> as i know), which results in incompatibility of many GIS systems with this
> botanical grid.
> 
> The closest solution is
> 
> +proj=eqdc +lat_1=52 +lat_2=52 +lat_0=52 +lon_0=19 +axis=esu +a=6390000
> +b=6390000 +ellps=sphere +x_0=330000 +y_0=-350000
> 
> ...but this results in quite significant inaccuracy, as EQDC is not
> gnomonic (central) projection.
> 
> So, my questions are:
> 
> 1. Is there a possibility to achieve desired projection using PROJ4 ?
> 2. If not, are there any possibility to implement such a functionality in
> the future to allow GIS users using this grid?
> 
> Thank you very much in advance
> 
> Lukasz Komsta
> 
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