[Qgis-user] Question on Project Properties - Ellipsoid

[Randal Hale]

On 7/13/20 7:41 PM, Greg Troxel wrote:
> 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.
I'd have to reload an older version - but it seems like before 3.10 (I'm 
on linux and was trailing on proj versions) that when I loaded some 2274 
data the ellipsoid was coming in wrong (not GRS80 and I can't remember 
what it was pulling in). In the testing this weekend it's coming in 
correctly (3.14) if I start out with a new profile etc etc - which 
further fueled the "I'm doing this wrong" line of thought.
>
> 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.
>
-- 
-----------
Randal Hale
rjhale at northrivergeographic.com
https://www.northrivergeographic.com
(423)653-3611