[PROJ] How does proj deal with ellipsoid with respect to reprojection

[Pierre Abbat]

On Sunday, 29 March 2020 02:28:57 EDT Lesparre, Jochem wrote:
> Doing point in polygon in a projection will result in occasional wrong
> conclusions. A point near de edge can seem to be inside the polygon while
> it's outside, or the other way around, since a straight line in the
> projection deviates from the geodesic.
 
> I analysed this problem for the Netherlands (51 - 55 degrees north) in the
> azimuthal projection (+proj=sterea) of the national coordinate reference
> system RD (epsg:28992) and in plate-caree projection (+proj=lonlat). The
> deviation depends on the length, orientation and location of a polygon
> segment. I computed the maximum possible deviation in the Netherlands for
> both projections to advise the Dutch government not to allow any segments
> longer than 200 m in a new digital storage system for policy and zoning
> borders.

When doing point in polygon in the spherical stereographic projection, you are 
checking circular arcs, not straight lines, in the plane. A geodesic projects 
to a circle. How much does a geodesic of an ellipsoid, projected conformally 
onto a sphere, differ from a geodesic of a sphere?

Pierre
-- 
When a barnacle settles down, its brain disintegrates.
Já não percebe nada, já não percebe nada.