Roger<br><br>The test data cannot be correct. ETRS89 coincides with WGS84 (or better ITRF) in 1989 and the current discplacement is only a few decimeters. The lat-long differences between your coordinates are 0.080" and 0.122", which correspond to approximately 2.9 m in lat and 2.5 m in long, i. e the differences you get in the projected coordinates.<br>
<br>Yout test point belongs to the portuguese geodetic network. The ETRS89 coordinates are correct, as you can check in:<br><br><a href="http://www.igeo.pt/produtos/geodesia/vg/rgn/ficha.asp?num=873">http://www.igeo.pt/produtos/geodesia/vg/rgn/ficha.asp?num=873</a><br>
(open with Internet Explorer)<br><br>Where did you get the WGS84 coordinates? They must be wrong.<br><br>Regards<br><br>José A. Gonçalves<br>Univ. of Porto, Portugal<br><br><br><br><div class="gmail_quote">2010/6/7 Roger Oberholtzer <span dir="ltr"><<a href="mailto:roger@opq.se">roger@opq.se</a>></span><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">On Thu, 2010-02-18 at 16:40 +0100, Roger Oberholtzer wrote:<br>
<br>
I now have some test data for the conversion from WGS84 lat/long to TM06<br>
northing/eastings. The suggested proj conversion of:<br>
<br>
"+proj=tmerc "<br>
"+ellps=GRS80 "<br>
"+k=1.0 "<br>
"+x_0=0 "<br>
"+y_0=0 "<br>
"+lon_0=-8.133108333333334 "<br>
"+lat_0=39.66825833333333 "<br>
"+towgs84=0,0,0,0,0,0,0 "<br>
<br>
seems in fact to work with ETRS89 lat/long, not WGS84 lat/long. When<br>
provided with WGS84 lat/long, the resulting northings/eastings are a few<br>
meters away. (Assuming my test data from the Portuguese Road Department<br>
is correct. I have double checked, so it might very well be.) In fact,<br>
it is a small error, but I want to provide the best I can. I am guessing<br>
that I need to change my +towgs84= to cause the WGS84 lat/longs to be<br>
converted to ETRS89. Does anyone know the proper values?<br>
<br>
This begs the question: what does<br>
<a href="http://spatialreference.org/ref/epsg/3763/" target="_blank">http://spatialreference.org/ref/epsg/3763/</a> assume is the datum of the<br>
original lat/longs? Seems it assumes ETRS89, not WGS84.<br>
<br>
Here is a sample location that I have been provided (all altitudes set<br>
to 0.0):<br>
<br>
Ref (WGS84): Latitude: 41.6743830556 Longitude: -8.3312663889<br>
Ref (ETRS98): Latitude: 41.6744052222 Longitude: -8.3312324722<br>
Ref (TM06): Easting: -16498.151 Northing: 222796.720<br>
<br>
The proj conversion above properly converts the ETRS98 locations to<br>
TM06. But I want to convert the WGS84 locations to TM06. When I try<br>
that, I get:<br>
<br>
Easting: -16500.981 Northing: 222794.265<br>
<br>
which is 3.747 meters away.<br>
<br>
--<br>
Roger Oberholtzer<br>
<br>
OPQ Systems / Ramböll RST<br>
<br>
Ramböll Sverige AB<br>
Krukmakargatan 21<br>
P.O. Box 17009<br>
SE-104 62 Stockholm, Sweden<br>
<br>
Office: Int +46 10-615 60 20<br>
Mobile: Int +46 70-815 1696<br>
<br>
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