[Qgis-user] Question on Project Properties - Ellipsoid

[Greg Troxel]

Nyall Dawson <nyall.dawson at gmail.com> writes:

> It's actually unrelated to projection. You CAN'T change the ellipsoid
> used by a projection, at least without creating your own custom
> projection.

That makes sense.

> The ellipsoid settings in project properties are only utilised for
> area/length calculations, not transformations.

So there is an implicit:

  when calculating length between two points, first convert them to some
  geodetic CRS (chosen how?)

  then use the configured ellipsoid to do the calculations, based on the
  two sets of lat/lon

?

Why is it useful/sound for someone to set an ellipsoid which is not the
ellipsoid used by the project CRS?