Dear Tyler!
proj4 projections definitions are stored on ubuntu in the file
/usr/share/proj/epsg, edit this file to add +geoidgrids=your_grid.
QGIS projection definitions are stored in a sqlite database, on ubuntu you
can find the srs.db in the /usr/share/qgis/resources directory.
You can update the record of a projection in this database.
I have sofar used +nadgrids for horizontal coordinates, I don't know if
QGIS allow +geogrids, too.
Try to update parameters column in tbl_srs table:
UPDATE tbl_srs SET parameters=parameters || ' +geoidgrids=your_gtx_file'
where srid=your_epsg_code;
Be careful, if you update your QGIS version you probably have to update
also the srs.db.
Best regards,
Zoltan
On Tue, 24 Oct 2017, Tyler Veinot wrote:
Since you guys both know more about PROJ4 than I do I thought I would just
tag this question on;
Where is QGIS/PROJ4 with support for vertical datums? Is there a way I can
attach a vertical datum to a CRS in PROJ4?
Tyler
On Mon, Oct 23, 2017 at 9:09 AM, Tyler Veinot <[email protected]>
wrote:
Andre;
It seems QGIS does not like my gsb file, I downloaded the NTV2 gsb from
NRCan and pointed to it and it worked. For some reason the one specific for
PEI does not. However, the grid shift could be the same as far as I know;
cannot find any information on what mathematical principles are used to
define the shift to correct the coordinates.
Tyler
On Mon, Oct 23, 2017 at 8:01 AM, André Joost <[email protected]> wrote:
Am 20.10.2017 um 20:19 schrieb Tyler Veinot:
Andre;
Again, sorry accidently sent the email mid writing. Where was I....
Right so I added
nadgrids=PE7783V2.gsb a number of ways trying to sort it based on online
information and how some other CRS's were setup within QGIS but nothing
worked yet.
It might be better to post the full string.
When I add the directory to my gsb where do I add it in the line and does
it need quotes?
If you have blanks in folder names, surely.
HTH,
André Joost
On Fri, Oct 20, 2017 at 2:55 PM, Andre Joost <[email protected]
wrote:
Am 20.10.2017 um 14:31 schrieb Tyler Veinot:
Anyone knowledge in using grid shift files (gsb) with QGIS?
I have a local CRS NAD27 Double Stereographic Imperial that I need to
transform to NAD83 CSRS 2010 Epoch. I have the CRS properly defined
using
the provincial description
Can you add your custom CRS? Maybe you have +datum=nad27 which uses the
main nadcon transformation file. use +ellps=clrk66
+nadgrids=/path/to/your/file
but QGIS using its Clark 1866 to GRS80
transformation puts the points a little off from the NTV2 coordinate
transformation software we have. I have the GSB used (even though it
says
ATS77 the provincial geomatics guys tell me it shits NAD27 and ATS77
into
CSRS 2010 NAD83). I followed some directions on putting the file in a
specific folder and restarted QGIS set the settings to always ask for
grid
shift file for transformations yet I do not see the one I put in there
in
my list to pick from.
Can you explain where that setting should be?
I also tried to install a plugin for NTV2 transformations but cannot
activate it. When I go to Activate Additional Providers in my
Processing
Toolbox where NTv2 Datum Transformations resides I get the "Specified
Path
does not exist: C:\PROGA~1\QGIS~1.18\bin" error that I have not yet
managed
to resolve. To my understanding has something to do with GRASS plugins
and
past versions of QGIS.
You can workaround that GRASS error by creating that folder, or changing
the folder entry for GRASS 7 to an existing folder.
But to use your grid in the plugin, you would need some python code
around
it, like the other grids have in C:\Users\<username>\.qgis2\pyt
hon\plugins\ntv2_transformations
Without that processing would not know about your grid.
HTH,
André Joost
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