[Qgis-user] NTV2 Grid Shits

[Siki Zoltan]

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 <tylerkveinot at gmail.com>
> 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 <andre.joost at arcor.de> 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 <andre+joost at nurfuerspam.de
>>>>>
>>>> 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
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Qgis-user mailing list
>>>>> Qgis-user at lists.osgeo.org
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>>>>>
>>>>>
>>>>
>>>
>>>
>>
>