<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Gentlemen,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Thanks very much for looking into my "headache" problem. I never found the "cct" option neither the "+exact " option regarding the helmert transformation. I can now more or less use the trimble coefficient to get a proper transformation (within 2-3 cm) . At least within the OSgeo proj4 system. The next step is to get this working in Qgis!!?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Kind regards,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Michel</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">echo -63.25156367 17.61578594 -41.194 |cct +proj=pipeline +step +proj=cart +ellps=WGS84 +step +proj=helmert +convention=coordinate_frame +x=194.245 +y=-154.53 +z=102.676 +rx=351.5046 +ry=-701.841 +rz=251.9889 +s=6.296557 +exact +step +proj=cart +inv +ellps=intl +step +proj=tmerc +units=m +lat_0=17.63621319 +lon_0=-63.23752013 +x_0=4714.87 +y_0=1967.19 +k_0=1.0<br> 3215.4356 -287.5511 2.0691 inf<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Op vr 2 aug. 2019 om 10:54 schreef Kristian Evers <<a href="mailto:kreve@sdfe.dk">kreve@sdfe.dk</a>>:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Nick,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">With the helmert [0] operation you can choose to use either the small angle approximation or the full set of equations. Enable the full equations with the +exact
flag.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Michel,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">I haven’t studied you email closely, but at least I can see that in your example with the pipeline you are using proj where should be using cct. The reason being
that proj only works in 2D and you are asking for a 3D transformation. Generally, proj should only be used for projection of geodetic coordinates.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">/Kristian<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="DA" style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">[0]
</span><a href="https://proj.org/operations/transformations/helmert.html" target="_blank"><span lang="DA">https://proj.org/operations/transformations/helmert.html</span></a><span lang="DA" style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u><u></u></span></p>
<p class="MsoNormal"><span lang="DA" style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span style="font-size:11pt;font-family:Calibri,sans-serif">From:</span></b><span style="font-size:11pt;font-family:Calibri,sans-serif"> PROJ <<a href="mailto:proj-bounces@lists.osgeo.org" target="_blank">proj-bounces@lists.osgeo.org</a>>
<b>On Behalf Of </b>Nick Mein<br>
<b>Sent:</b> 2. august 2019 10:45<br>
<b>To:</b> Michel Ruijter <<a href="mailto:mnrengineering@gmail.com" target="_blank">mnrengineering@gmail.com</a>><br>
<b>Cc:</b> <a href="mailto:PROJ@lists.osgeo.org" target="_blank">PROJ@lists.osgeo.org</a><br>
<b>Subject:</b> Re: [PROJ] CRS for small Island (Saba), conversion of known projection and transformation parameters (Trimble) into proj4 string<u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">There was a long discussion in this mailing list back in 2017 about 7 parameter transformations with large rotations. You can find the discussion at <a href="http://osgeo-org.1560.x6.nabble.com/towgs84-approximation-error-td5313738.html" target="_blank">http://osgeo-org.1560.x6.nabble.com/towgs84-approximation-error-td5313738.html</a>.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">I'm not sure that there was ever a resolution to the discussion. But if PROJ is still using small-angle approximations for 7 parameter transformations then that is probably the reason that it isn't giving the expected results?<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Fri, 2 Aug 2019 at 03:39, Michel Ruijter <<a href="mailto:mnrengineering@gmail.com" target="_blank">mnrengineering@gmail.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif">Ls,<br>
For a small Caribbean Island (Saba) I am trying to get the proper proj4 CRS (for Qgis) in order to use GPS based coordinates on local grid related system<br>
The following projection and datum parameters are used in a TRimble software package (and used in the RTK equipment) in local "Kadaster" coordinates to set out benchmarks etc<br>
<br>
Ellipsoid<br>
Ellipsoid Name : (WGS 84) <br>
Flattening 1/f : 297.000 <br>
Semi Major Axis : 6378388.000m <br>
<br>
<br>
Datum Transformation : Seven Parameter<br>
WGS84 to (WGS 84) (sounds a little bit confusing since ellipsoid seems to be the international ellipsoid<br>
Translation X : 194.245m Rotation X : 0°05'51.504629" <br>
Translation Y : -154.530m Rotation Y : -0°11'41.841439"<br>
Translation Z : 102.676m Rotation Z : 0°04'11.988863"<br>
Scale Factor : 6.2965571264 ppm<br>
<br>
<br>
Transverse Mercator Projection<br>
Projection Origin False Origin<br>
Latitude : 17°38'10.36749"NFalse Northing : 1967.190m<br>
Longitude : 63°14'15.07247"WFalse Easting : 4714.870m<br>
Height : N/A False Elevation : N/A<br>
Scale Factor : 1.00000000<br>
<br>
Test coordinates: <br>
WGS84 in°N WGS84 in°E z(ellips) LocalE in m LocalN in m Z(msl)<br>
1 17.61578594 -63.25156367 -41.19 3215.38 -287.59 2.065<br>
2 17.62323214 -63.23827421 290.27 4629.098 530.823 333.55<br>
<br>
These coordinates have been verified with pctrans (software of the dutch navy) and the conversion (Trimble) seems to be good to within 2 cm<br>
<br>
I have tried to convert the translation rotation and projection into a proj4 structure within Qgis<br>
I converted the rotation into arcseconds:<br>
<br>
Rotation X : 0°05'51.504629" (351.504629")<br>
Rotation Y : -0°11'41.841439" (-701.841439")<br>
Rotation Z : 0°04'11.988863" (251.988863")<br>
<br>
+proj=tmerc +lat_0=17.63621319 +lon_0=-63.23752013 +k=1 +x_0=4714.870 +y_0= 1967.19 +ellps=intl +towgs84=194.245,-154.53,102.676,-351.5046,701.841,-251.9889,6.296557 +units=m +no_defs<br>
<br>
(note all signs of of rotation have been changed compared to Trimble notation )<br>
<br>
application of this proj4 string in Qgis results in the following two local grid positions:<br>
1 3250.9 mE -209.59mN<br>
2 4658.157mE 620.26 mN <br>
<br>
I also tried to use OS4GEO installed on a win10 machine in many variants e.g.<u></u><u></u></span></p>
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echo -63.25156367 17.61578594 |cs2cs +proj=latlong +ellps=WGS84 +towgs84=0,0,0 +no_defs +to +proj=tmerc +ellps=WGS84 +lat_0=17.63621319 +lon_0=-63.23752013 +k=1 +x_0=4714.87 +y_0=1967.19 +towgs84=-194.245,154.53,-102.676,-351.5046,701.841,-251.9889,-6.296557
+units=m +no_defs<br>
<br>
with as a result x=3458.54 y=-202.09 z=286.19<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif">I have tried to use the pipeline option as well however, in one of the first steps OSgeo seems not to convert coordinates properly:<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif">e.g. with the statement below I expect to get 17.00 17.00 as an answer but I get 17.00 0.00 !!!<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif"> <u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif">echo 17.0 17.0 | proj +proj=pipeline +step +proj=cart +ellps=intl +step +proj=cart +inv +ellps=intl<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:Arial,sans-serif"><br>
<br>
I have tried a number of versions of this transformation (changing signs in the towgs string string but this does not result in proper coordinates.<br>
<br>
What is wrong with this proj4 string based on the rotation and projection information from the Trimble software and how in general can we use the translation and projection information into a valid proj4 string?<br>
<br>
Kind regards,<br>
<br>
Michel Ruijter<br clear="all">
<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">-- <u></u><u></u></p>
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<p class="MsoNormal">Michel Ruijter<u></u><u></u></p>
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<p class="MsoNormal">MNRengineering<u></u><u></u></p>
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<p class="MsoNormal">de Kempenaerstraat 82, 2341GP, Oegstgeest<u></u><u></u></p>
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<p class="MsoNormal">mob: +31638944484, tel: +31718897137<u></u><u></u></p>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">Michel Ruijter<div>MNRengineering</div><div>de Kempenaerstraat 82, 2341GP, Oegstgeest</div><div>mob: +31638944484, tel: +31718897137</div></div></div></div></div></div></div>