Re: [Qgis-user] NTV2 Grid Shits

[TYlerVeinot]

I have no need to transform from ATS77 to NAD27 but it sounds like a good
idea if one had to. I have 2 GSB Files PE7783V2.gsb from the GeoCalc
Software designed by GeoNB for PEI to transform from ATS77 to NAD83 and
NTv2.gsb which is a national gsb for going from NAD27 to NAD83. I came back
to this post because after installing QGIS3 and removing QGIS2 I lost all my
old custom CRS's that were tied into using those GSB's to transform
coordinates, and they seemed to work because the coordinates were slightly
different than if I did not have the +XYZ.gsb in the PROJ4.
I am trying to add my new gsb files directly to the srs database so that
they come up as transformation options in QGIS3. I added them to the
database table but they do not come up as options in the CRS screen. Has
anyone tried adding it directly?



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Re: [Qgis-user] NTV2 Grid Shits

[stevejking]

Tyler,
I think the following might work.

Pick up the NAD27toATS77 and ATS77toNAD83 here:
http://georepository.com/search/by-name/query/Ats77/transformation_page/1/#transformation

Add the two multiband grids together somehow (open gsb's as raster in qgis)
i.e. Band 1 longitude shift and band 2 latitude shift. The other two bands
can be zero. Save the new grid as a multi band geotif.

From a command prompt Navigate to gdal_translate located in QGIS 2.16\Bin\
or equivalent
Then type:
gdal_translate  -of NTV2 

This will create new_ntv2_grid.gsb which will be NAD27toNAD83 ( a proxy for
wgs84 as far as proj4 is concerned).

Just remember to put the gsb on your from string, and your to string
+towgs84=0,0,0,0,0,0,0



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Re: [Qgis-user] NTV2 Grid Shits

[Andre Joost]

Am 24.10.2017 um 22:42 schrieb stevejking:

Tyler,
  NAD27 and ATS77 don't seem to share the same ellipsoid.
spatialreference.org lists ATS77 as
+proj=sterea +lat_0=47.25 +lon_0=-63 +k=0.12 +x_0=70 +y_0=40
+a=6378135 +b=6356750.304921594 +units=m +no_defs

It's missing a +towgs84= or +nadgrids= BUT Notice the ellipsoid a and b
parameters do not match the NAD27 clarke66 ellipsoid. So a nadgrids shift
file for NAD27, will not work for ATS77.



See 
https://knowledge.safe.com/articles/815/datum-and-grid-shift-for-canadian-provinces-new-br.html 
and 
https://knowledge.safe.com/articles/789/where-to-source-canadian-grid-shift-files-not-incl.html


HTH,
André Joost


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Re: [Qgis-user] NTV2 Grid Shits

[stevejking]

Tyler,
 NAD27 and ATS77 don't seem to share the same ellipsoid.
spatialreference.org lists ATS77 as 
+proj=sterea +lat_0=47.25 +lon_0=-63 +k=0.12 +x_0=70 +y_0=40
+a=6378135 +b=6356750.304921594 +units=m +no_defs 

It's missing a +towgs84= or +nadgrids= BUT Notice the ellipsoid a and b
parameters do not match the NAD27 clarke66 ellipsoid. So a nadgrids shift
file for NAD27, will not work for ATS77.

Steve



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Re: [Qgis-user] NTV2 Grid Shits

[stevejking]

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Re: [Qgis-user] NTV2 Grid Shits

[stevejking]

Last I checked QGIS 2.14 ignored any +geoidgrid=
But it works fine in various stand alone Proj4 tools.

Alternatively, any nadgrids and any geoidgrids files will open in QGIS as
raster grids, so you can use them that way too. For example A gsb file will
be multi band, latitude shift, longitude shift (usually arc seconds of a
degree), and two error values usually set to zero. And for example a GTX
file will be a grid of vertical shifts usually to the WGS84 or GRS80
ellipsoid. Both grid files need to be realised on the CRS native ellipsoid
in latlong coordinates, ie. not necessarily on WGS84 ellipsoid. Note some
nadgrids files are produced in the reverse direction, but proj4 assumes
shifts are to WGS84 from the CRS ellipsoid.

Steve


Siki Zoltan wrote
> Dear Tyler!
> 
> , I don't know if
> QGIS allow +geogrids, too...
> 
> 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@

> 
>> 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@

>  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@

> 
> 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\
> 
> \.qgis2\pyt
>> hon\plugins\ntv2_transformations
>> Without that processing would not know about your grid.
>>
>> HTH,
>> André Joost
>>
>>
>>
>> ___
>> Qgis-user mailing list
>> 

> Qgis-user@.osgeo

>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
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>


>>>
>>
> 

Re: [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 
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  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 

Re: [Qgis-user] NTV2 Grid Shits

[Tyler Veinot]

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 
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  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 >> >
>>> 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\\.qgis2\pyt
 hon\plugins\ntv2_transformations
 Without that processing would not know about your grid.

 HTH,
 André Joost



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>>>
>>
>>
>
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Re: [Qgis-user] NTV2 Grid Shits

[Andre Joost]

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\\.qgis2\python\plugins\ntv2_transformations

Without that processing would not know about your grid.

HTH,
André Joost


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