Re: [Qgis-user] Custom CRS - adding a rotation

[Paul Paris]

GRASS's v.transform:
https://grass.osgeo.org/grass70/manuals/v.transform.html might also be
useful here.

Paul

On Thu, Apr 6, 2017 at 11:10 AM, Andre Joost 
wrote:

> Am 05.04.2017 um 20:46 schrieb Brock Riedell:
>
>> I have some downloaded geologic map shapefiles that were digitized
>> incorrectly in UTM space, and they render a few hundred meters away from
>> their proper locations on georeferenced U.S. topo maps as well as on
>> Google, Bing, and ESRI online base map data. This is too much for datum
>> shift; the NAD27 to NAD83 transformation should offset coordinates about
>> 90 m.  I have determined that the correction involves a counterclockwise
>> rotation of ~1.4 degrees and not a simple translation. I have reviewed
>> the PROJ.4 documentation about using the 7-parameter 'towgs84' options
>> to add the rotation.  I have not been able to get this working by trial
>> and error; the data plot out 150-200 km away from where they should be.
>> Questions:
>>
>> (1) Do I need to input the rotation value as both Rx and Ry?
>> (2)The documentation says rotations are input as seconds of arc rather
>> than degrees, correct?
>> (3) How does the scaling parameter in towgs84 interact with the scale
>> factor k_0?
>>
>
> The towgs84 parameters are really ment for small rotations only. If you
> have big rotations, think of using a custom oblique mercator transformation.
>
> You can find an example at http://gis.stackexchange.com/q
> uestions/83861/using-customized-coordinate-system-in-arcgis-desktop
>
> HTH,
> André Joost
>
>
> ___
> Qgis-user mailing list
> Qgis-user@lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
___
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user

Re: [Qgis-user] Custom CRS - adding a rotation

[Fernando M. Roxo da Motta]

On Wed, 5 Apr 2017 11:46:57 -0700, Brock Riedell  wrote:


> I have some downloaded geologic map shapefiles that were digitized 
> incorrectly in UTM space, and they render a few hundred meters away
> from their proper locations on georeferenced U.S. topo maps as well
> as on Google, Bing, and ESRI online base map data. This is too much
> for datum shift; the NAD27 to NAD83 transformation should offset
> coordinates about 90 m.  I have determined that the correction
> involves a counterclockwise rotation of ~1.4 degrees and not a simple
> translation. I have reviewed the PROJ.4 documentation about using the

  It seems that it fits completely the definition of an affine
transformation.   There is a plugin with this name that should do the
magic.


  HTH


> 7-parameter 'towgs84' options to add the rotation.  I have not been
> able to get this working by trial and error; the data plot out
> 150-200 km away from where they should be. Questions:
> 
> (1) Do I need to input the rotation value as both Rx and Ry?
> (2)The documentation says rotations are input as seconds of arc
> rather than degrees, correct?
> (3) How does the scaling parameter in towgs84 interact with the scale 
> factor k_0?
> 
> 
> Thanks and regards
> Brock
> 
> 








  Roxo

-- 
 Non luctari, ludare ---+ WYSIWYG
Fernando M. Roxo da Motta   | Editor?
Except where explicitly stated I speak on my own behalf.|  VI !!
  ( Usuário Linux registrado #39505 )   | I see text,
 Quis custodiet ipsos custodes?-+ I get text!
 
___
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user

Re: [Qgis-user] Custom CRS - adding a rotation

[Andre Joost]

Am 05.04.2017 um 20:46 schrieb Brock Riedell:

I have some downloaded geologic map shapefiles that were digitized
incorrectly in UTM space, and they render a few hundred meters away from
their proper locations on georeferenced U.S. topo maps as well as on
Google, Bing, and ESRI online base map data. This is too much for datum
shift; the NAD27 to NAD83 transformation should offset coordinates about
90 m.  I have determined that the correction involves a counterclockwise
rotation of ~1.4 degrees and not a simple translation. I have reviewed
the PROJ.4 documentation about using the 7-parameter 'towgs84' options
to add the rotation.  I have not been able to get this working by trial
and error; the data plot out 150-200 km away from where they should be.
Questions:

(1) Do I need to input the rotation value as both Rx and Ry?
(2)The documentation says rotations are input as seconds of arc rather
than degrees, correct?
(3) How does the scaling parameter in towgs84 interact with the scale
factor k_0?


The towgs84 parameters are really ment for small rotations only. If you 
have big rotations, think of using a custom oblique mercator transformation.


You can find an example at 
http://gis.stackexchange.com/questions/83861/using-customized-coordinate-system-in-arcgis-desktop


HTH,
André Joost


___
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user

[Qgis-user] Custom CRS - adding a rotation

[Brock Riedell]

I have some downloaded geologic map shapefiles that were digitized 
incorrectly in UTM space, and they render a few hundred meters away from 
their proper locations on georeferenced U.S. topo maps as well as on 
Google, Bing, and ESRI online base map data. This is too much for datum 
shift; the NAD27 to NAD83 transformation should offset coordinates about 
90 m.  I have determined that the correction involves a counterclockwise 
rotation of ~1.4 degrees and not a simple translation. I have reviewed 
the PROJ.4 documentation about using the 7-parameter 'towgs84' options 
to add the rotation.  I have not been able to get this working by trial 
and error; the data plot out 150-200 km away from where they should be. 
Questions:


(1) Do I need to input the rotation value as both Rx and Ry?
(2)The documentation says rotations are input as seconds of arc rather 
than degrees, correct?
(3) How does the scaling parameter in towgs84 interact with the scale 
factor k_0?



Thanks and regards
Brock


___
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user