<div dir="ltr">I downloaded the grid shift file from <a href="http://www.kadaster.nl/transformatie-van-coordinaten">http://www.kadaster.nl/transformatie-van-coordinaten</a><br><br>I am not using it yet. I took one of the sample points from the Use doc that came with it to see what I got compared to the expected. For example:<br><br><font size="1"><span style="font-family:monospace,monospace">Zuid-Limburg:<br> Ref: Latitude: 50.7925849160 Longitude: 5.7737955480 Altitude: 245.948<br> Ref: Easting: 182260.450 Northing: 311480.670 Altitude: 200.000<br> Proj4: Easting: 182225.909 Northing: 311388.163 Altitude: 245.948 98.746 meters from Ref<br></span></font><div class="gmail_extra"><br>The reference values are ETRS89. But I cannot think that accounts to 100 meters of difference. My proj spec is:<br><br> +proj=sterea <br> +lat_0=52.15616055555555 <br> +lon_0=5.38763888888889 <br> +k=0.9999079<br> +x_0=155000 <br> +y_0=463000 <br> +ellps=bessel <br> +towgs84=565.4174,50.3319,465.5542,-0.398957388243134,0.343987817378283,-1.87740163998045,4.0725<br> +units=m <br> +no_defs<br><br></div><div class="gmail_extra">Doing this via the C API as I do for many other projections. These are passed to pj_init_plus.<br></div><div class="gmail_extra"><br></div><div class="gmail_extra">Would the grid shift make such a large correction?<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Nov 1, 2016 at 12:51 PM, Bas Couwenberg <span dir="ltr"><<a href="mailto:sebastic@xs4all.nl" target="_blank">sebastic@xs4all.nl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="gmail-HOEnZb"><div class="gmail-h5">On 2016-11-01 12:33, Roger Oberholtzer wrote:<br>
> I am trying to get the Amersfoort / RD New projection working with<br>
> proj4. The users (a road authority in the Netherlands) claim to use<br>
> this definition with ESRI:<br>
><br>
> PROJCS["RD_New",GEOGCS["GCS_<wbr>Amersfoort",DATUM["D_<wbr>Amersfoort",<br>
> SPHEROID["Bessel_1841",<wbr>6377397.155,299.1528128]],<br>
> PRIMEM["Greenwich",0.0],<br>
> UNIT["Degree",0.<wbr>0174532925199433]],<br>
> PROJECTION["Double_<wbr>Stereographic"],<br>
> PARAMETER["False_Easting",<wbr>155000.0],<br>
> PARAMETER["False_Northing",<wbr>463000.0],<br>
> PARAMETER["Central_Meridian",<wbr>5.38763888888889],<br>
> PARAMETER["Scale_Factor",0.<wbr>9999079],<br>
> PARAMETER["Latitude_Of_Origin"<wbr>,52.15616055555555],UNIT["<wbr>Meter",1.0]]<br>
><br>
> I have started with the definition at<br>
> <a href="http://spatialreference.org/ref/epsg/amersfoort-rd-new/proj4/" rel="noreferrer" target="_blank">http://spatialreference.org/<wbr>ref/epsg/amersfoort-rd-new/<wbr>proj4/</a>. The<br>
> projections from that are 100 meters from where they should be. I have<br>
> seen claims that the Spatial Reference definition is incorrect, and<br>
> that a better one is (it adds the +towgs84):<br>
><br>
> “+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889<br>
> +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel<br>
> +towgs84=565.4174,50.3319,465.<wbr>5542,-0.398957388243134,0.<wbr>343987817378283,-1.<wbr>87740163998045,4.0725<br>
> +units=m +no_defs”<br>
><br>
> Still no joy. My source values are WGS84 lat/long from a GPS receiver.<br>
><br>
> Anyone have the correct proj4 definition for this?<br>
<br>
</div></div>The +towgs84 parameters as published by the Dutch Kadaster are:<br>
<br>
+towgs84=565.4171,50.3319,465.<wbr>5524,-0.398957,0.343988,-1.<wbr>877402,4.0725<br>
<br>
These are used in the epsg file from PROJ.4 4.9.3, see:<br>
<br>
<a href="https://github.com/osgeonl/rdprojectie/blob/master/doc/ntv2grid.md" rel="noreferrer" target="_blank">https://github.com/osgeonl/<wbr>rdprojectie/blob/master/doc/<wbr>ntv2grid.md</a><br>
<br>
Alternatively you can use the RDNAP grid shift files also published by<br>
Kadaster. If you're on Debian/Ubuntu you can install the proj-rdnap<br>
package (available in jessie-backports/non-free and Ubuntu wily and<br>
later), otherwise you can find the download link in the PROJ.4<br>
documentation at:<br>
<br>
<a href="http://proj4.org/grids.html#netherlands" rel="noreferrer" target="_blank">http://proj4.org/grids.html#<wbr>netherlands</a><br>
<a href="http://www.kadaster.nl/transformatie-van-coordinaten" rel="noreferrer" target="_blank">http://www.kadaster.nl/<wbr>transformatie-van-coordinaten</a><br>
<br>
Use the link in the "Benadering transformatieprocedure" section to go to<br>
the request package and fill in the form. You'll be sent a download link<br>
by email.<br>
<br>
We've recently had a mini-seminar about the correct usage of RD in open<br>
source software, and started collecting reference information resulting<br>
from that in a git repository:<br>
<br>
<a href="https://github.com/osgeonl/rdprojectie" rel="noreferrer" target="_blank">https://github.com/osgeonl/<wbr>rdprojectie</a><br>
<br>
You'll find more information in the linked posts on the Dutch<br>
mailinglist.<br>
<br>
Kind Regards,<br>
<br>
Bas<br>
______________________________<wbr>_________________<br>
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<a href="http://lists.maptools.org/mailman/listinfo/proj" rel="noreferrer" target="_blank">http://lists.maptools.org/<wbr>mailman/listinfo/proj</a></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature">Roger Oberholtzer</div>
</div></div>