Re: [Qgis-user] vector shp from NAD83 (CSRS98) to UTM WGS84

Thu, 31 Mar 2016 08:09:12 -0700 

Hi Andreas, 
That is very interesting. I would like to know more about these grids and how 
QGIS deals with it.  Do you have any additional links to share? 
All I can see is that the proj4 parameters for many of the CRS in North America 
are identical and lead to no actual changes in the coordinate unless you are 
going from nad27 to nad 83 or Wgs84 which is more drastic. 
That is why I use the nrcan tool that can do transformation based on  ITRF 
and WGS84 CRS. 
I would be nice to do that strait in QGIS. I will look into your method and 
report back. 
Nicolas 
On Mar 31, 2016 10:24 AM, "Neumann, Andreas [via OSGeo.org]        " 
<[email protected]> wrote: 
Hi Nicolas, 
That is not exactly true. 
QGIS can very well cope with grid-shift based transformations. This requires an 
adequate grid shift file (a gsb file), which should be placed in the folder 
share/proj 
National mapping agencies typically provide these grid-shift files. As an 
example, our Swiss NMA provides these at  
http://www.swisstopo.admin.ch/internet/swisstopo/en/home/products/software/products/chenyx06.html
   
QGIS automatically detects whether a grid shift file is necessary for a 
transformation and if the appropriate gsb files is present it is used. The 
accuracy of the transformation then depends on the grid-shift file accuracy 
(resolution). 
The grid shift files can be used both for reprojecting vector and raster data. 
Greetings, 
Andreas 
On 2016-03-31 15:54, Nicolas Cadieux wrote: 

Hi,  It is my understanding that the parameters used in QGIS for that 
transformation are not sufficient  and will simply lead to a change in EPGS 
code number with no actual changes to the coordinates. 
If you are dealing with data in the 20k to 250k (like topo maps, SRTM), you can 
go ahead with that. Difference between both projection are basically due to 
continental drift and the addition of the third dimension. 
For anything submeter (Lidar, high precision GPS) I recommend using a more 
precise software.  I know that nrcan has good free tools for changing 
projection but I don't know if they handle anything else then points (TRX) 
I think.  Look at the links below for more information if needed.  File is 
included in attachment. 
Nicolas 
http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/10925
 
https://www.google.ca/url?sa=t&source=web&rct=j&url=http://www.naref.org/transf/nad83_geomatica2006.pdf&q=csrs98%20nad83&ved=0ahUKEwiex4GHiOvLAhUEdx4KHb0NAwcQFggpMAU&usg=AFQjCNHa-HRpS8Hcc1j74dAysyxgobNY1w&sig2=RRPnudp1rMyhmKYd7vbdoA
 
On Mar 31, 2016 8:20 AM, "Joris Hintjens [via OSGeo.org] " <[hidden 
email]> wrote: 
simply save the layer as a new one. "save as". you will be asked to 
enter the new CRS.
  
joris 



Op 30 mrt. 2016, om 06:06 heeft Azzurra Lentini <<a 
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Hallo to all, 
do you know how I can transform vectorial data from NAD83 (CSRS98) to UTM 
wgs84? 
do you think if I do with reproject it would be ok?? or what u suggest?? 
  
thanks a lot  
  
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