[Qgis-user] Question on Project Properties - Ellipsoid

[Greg Troxel]

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

> On Tue, 14 Jul 2020 at 05:59, Randal Hale
> <rjhale at northrivergeographic.com> wrote:
>>
>> I hope everyone is staying safe out there.
>>
>> So I've had some questions regarding setting up a QGIS Project and now
>> I've convinced myself that I'm doing this wrong. When I get a new
>> project in and I start setting up QGIS generally my project will be in a
>> Stateplane projection - in this case EPSG:2274 (TN Stateplane NAD83).
>> When I set up the project I change the ellipsoid to be
>> "none/planimetric" (In the project properties). I don't set up the
>> ellipsoid to be GRS 1980 and haven't for some time.
>
> Can I ask why you do this?

I too am boggled by this.  EPSG:2274 is a Lambert Conformal Conic
projection of NAD83, and I don't understand what it means to do that
projection to/from geodetic coordinates without an ellipsoid definition.
Using the GRS80 ellipsoid is part of the definition of this CRS, so if
you change that you are using a different CRS that is not actually 2274,
and that 2274prime CRS should throw an exception if you try to convert
to/from NAD83 geodetic.

So I'd say the bug is qgis/proj allowing transforms to/from a
LCC-but-no-ellipsoid CRS.   And maybe qgis allowing
2274-but-no-ellipsoid is a bug too.