<p dir="ltr">Hi Andreas,</p>
<p dir="ltr">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?</p>
<p dir="ltr">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.</p>
<p dir="ltr">That is why I use the nrcan tool that can do transformation based on ITRF and WGS84 CRS.</p>
<p dir="ltr">I would be nice to do that strait in QGIS. I will look into your method and report back.</p>
<p dir="ltr">Nicolas</p>
<div class="gmail_quote">On Mar 31, 2016 10:24 AM, "Neumann, Andreas [via OSGeo.org] " <<a href="/user/SendEmail.jtp?type=node&node=5259013&i=0" target="_top" rel="nofollow" link="external">[hidden email]</a>> wrote:<br type='attribution'><blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p>Hi Nicolas,</p>
<p>That is not exactly true.</p>
<p>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</p>
<p>National mapping agencies typically provide these grid-shift files. As an example, our Swiss NMA provides these at <a href="http://www.swisstopo.admin.ch/internet/swisstopo/en/home/products/software/products/chenyx06.html" target="_top" rel="nofollow" link="external">http://www.swisstopo.admin.ch/internet/swisstopo/en/home/products/software/products/chenyx06.html</a> </p>
<p>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).</p>
<p>The grid shift files can be used both for reprojecting vector and raster data.</p>
<p>Greetings,</p>
<p>Andreas</p>
<p>On 2016-03-31 15:54, Nicolas Cadieux wrote:</p>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em">
<p dir="ltr">Hi,<br /> 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.</p>
<p dir="ltr">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.</p>
<p dir="ltr">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.</p>
<p dir="ltr">Nicolas</p>
<p dir="ltr">http://www.nrcan.gc.ca/earth-sciences/geomatics/geodetic-reference-systems/tools-applications/10925</p>
<p dir="ltr">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</p>
<div class="elided-text">On Mar 31, 2016 8:20 AM, "Joris Hintjens [via OSGeo.org] " <[hidden email]> wrote:<br />
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em">simply save the layer as a new one. "save as". you will be asked to enter the new CRS.
<div> </div>
<div>joris</div>
<div><br />
<div>
<blockquote style='border-left:2px solid #CCCCCC;padding:0 1em' style="border-left:2px solid #cccccc;padding:0 1em">
<div>Op 30 mrt. 2016, om 06:06 heeft Azzurra Lentini <<a href="/user/SendEmail.jtp?type=node&node=5258986&i=0">[hidden email]> het volgende geschreven:</div>
<br />
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<div dir="ltr">
<div style="font-family:'tahoma' , sans-serif">Hallo to all,</div>
<div style="font-family:'tahoma' , sans-serif">do you know how I can transform vectorial data from <span style="font-size:12.8px;font-family:'arial' , sans-serif">NAD83 (CSRS98) to UTM wgs84?</span></div>
<div style="font-family:'tahoma' , sans-serif"><span style="font-size:12.8px;font-family:'arial' , sans-serif">do you think if I do with reproject it would be ok?? or what u suggest??</span></div>
<div style="font-family:'tahoma' , sans-serif"><span style="font-size:12.8px;font-family:'arial' , sans-serif"> </span></div>
<div style="font-family:'tahoma' , sans-serif"><span style="font-size:12.8px;font-family:'arial' , sans-serif">thanks a lot </span></div>
<div> </div>
-- <br />
<div>
<div dir="ltr">Dr. Hydrogeologist <br />AZZURRA LENTINI<br />Expert of evaluation environmental hazards<br />GIS application <br />Haity Mobile Tel: 0050946057393<br />++++++++++++++++++++++++++<br />Italy Mobile Tel.: **(39) 338 24 40 676<br />++++++++++++++++++++++++++<br />SKYPE azzurrahydro<br />++++++++++++++++++++++++++<br /><a href="/user/SendEmail.jtp?type=node&node=5258986&i=1">[hidden email]<br />++++++++++++++++++++++++++<br />*Par respect pour l'environnement,*<br /><br />*n'imprimez ce mail qu'en cas d'absolue nécessité*<br /><br /> <br /><br /><br /><br /><br /></div>
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