Nyall had requested I submit a bug report...which I forgot
about....until now soooo -> https://github.com/qgis/QGIS/issues/34983
I added your explanation as a comment to the original email.
Randy
I added your message as a comment
On 3/10/20 2:09 PM, Michael.Dodd wrote:
Is there any more news on this 'bug' as it appears to be serious or it
might simply be the wording.
Example:
Project created in old version of qgis and opened in recent version.
It comes up with the message about "Ballpark Transformations" and
suggests installing proj-datumgrid-europe-1.5.zip to enable a better
transformatoin between epsg:27700 and epsg:4326. The project contains
the OS GB1936 system and WGS84.
So I installed the relevant .gsb files in the correct directory with
the other .gsb files, restarted and tried again to open the project.
This time it did not come up with the message suggesting the download
but instead just suggested using one of the other transformations
which are less accurate than the proper OSTN15_NTv2 transformation.
Need to know why it is doing the less accurate transformation and how
to get it to do the correct transformation instead.
------------------------------------------------------------------------
*From:* Qgis-user <qgis-user-boun...@lists.osgeo.org> on behalf of
Randal Hale <rjh...@northrivergeographic.com>
*Sent:* 27 February 2020 17:56
*To:* qgis-user@lists.osgeo.org <qgis-user@lists.osgeo.org>
*Subject:* [Qgis-user] Question On "BallPark Transform"
CAUTION: This mail comes from outside the University. Please consider
this before opening attachments, clicking links, or acting on the
content.
Greetings,
I received an email from two users with 3.12 asking about "Ballpark
Transformations" - the exact phrase was "Used a Ballpark
transformation from EPSG:4326 to EPSG: 2274".
I've been able to generate the message twice by:
* changing the projection of a new project with no data from 4326 to
2274
* adding data with an incorrect spatial extent that I believe was in
4326 and applied to a project in 2274 (I think - I currently don't
have access to that data to confirm)
I've found mention of it here:
https://qgis.org/api/classQgsCoordinateTransform.html#a16adb051fafc25058c0040a310f1606b
<https://qgis.org/api/classQgsCoordinateTransform.html#a16adb051fafc25058c0040a310f1606b>
The expanded message in QGIS is:
/*An alternative, ballpark-only transform was used when transforming
coordinates between *//*EPSG:4326 - WGS 84*//*and *//*EPSG:2274 -
NAD83 / Tennessee (ftUS)*//*. The results may not match those obtained
by using the preferred operation:*//**/
/*Possibly an incorrect choice of operation was made for
transformations between these reference systems. Check the Project
Properties and ensure that the selected transform operations are
applicable over the whole extent of the current project.*/
If I check the project properties there is no Datum Transformation
defined after all this happens.
I'm assuming that if a project has no data and one jumps datums by
changing the projection it's saying "Hey since there is no data this
transformation is a "ballpark" i.e. not exact". Is there a preferred
way to dealing with this after it happens?
Randy
--
Randal Hale
rjh...@northrivergeographic.com <mailto:rjh...@northrivergeographic.com>
(p) 423.653.3611
http://www.northrivergeographic.com
--
-----------
Randal Hale
rjh...@northrivergeographic.com
https://www.northrivergeographic.com
(423)653-3611
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