Thanks Mikael,<br><br>what if the Method is:<br><br><span class="propertyTitle emphasized_label"> </span> <div class="propertyValue show emphasized_content">Method [Geocentric translations (geog2D domain)]<br><br>and the Sign reversible field value is YES for all three parameters?<br>
<br><br>best regards,<br><br>Ilumas<br><br><br><br><br></div><br><br><div class="gmail_quote">On Fri, Apr 23, 2010 at 11:37 AM, Mikael Rittri <span dir="ltr"><<a href="mailto:Mikael.Rittri@carmenta.com">Mikael.Rittri@carmenta.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>
About the rotation sign conventions, I would<br>
add that calling the two conventions "European"<br>
and "American" is not helpful, since there is not<br>
much agreement about which convention is which!<br>
(Both conventions are used in Europe, and there<br>
is no obvious geographic pattern.)<br>
<br>
The terms "left-handed" and "right-handed" are<br>
just as bad.<br>
<br>
It is better to say that cs2cs uses the sign<br>
convention known as the<br>
<br>
Position Vector Transformation.<br>
<br>
If you look up the +towgs84 parameters on <a href="http://www.epsg-registry.org" target="_blank">www.epsg-registry.org</a><br>
(filter by Type: Coordinate Transformation), you will see the text<br>
<br>
"Warning: CARE! Ensure application uses this method! See Guidance Note<br>
7-1"<br>
<br>
above the parameter values. This means that you<br>
should scroll down _below_ the parameter values,<br>
where you find the Method. If it says:<br>
<br>
+ Method [Position Vector transformation]<br>
<br>
you can use the parameters directly in cs2cs.<br>
But if it says<br>
<br>
+ Method [Coordinate Frame Rotation]<br>
<br>
you should reverse the signs of the three<br>
rotation parameters.<br>
<br>
Best regards,<br>
<font color="#888888">--<br>
Mikael Rittri<br>
Carmenta AB<br>
SWEDEN<br>
<a href="http://www.carmenta.com" target="_blank">www.carmenta.com</a><br>
</font><div><div></div><div class="h5"><br>
-----Original Message-----<br>
From: <a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a><br>
[mailto:<a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a>] On Behalf Of Frank Warmerdam<br>
Sent: den 21 april 2010 18:14<br>
To: PROJ.4 and general Projections Discussions<br>
Subject: Re: [Proj] cs2cs's +towgs84 usage<br>
<br>
Ilumas wrote:<br>
> Dear list,<br>
><br>
> could you kindly confirm that the cs2cs's +towgs84 parameters remain<br>
> the same for a certain datum regardless of the direction of the<br>
> transformation. Some people (e.g.<br>
> <a href="http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberl" target="_blank">http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberl</a><br>
> y-td3410479.html)<br>
> <<a href="http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propber" target="_blank">http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propber</a><br>
> ly-td3410479.html>seem to suggest that the values need to be negated<br>
> when going FROM wgs84 TO something else, but this seems a bit strange<br>
> to me. Unfortunately all the examples in the man pages seem to be<br>
> about changing the coordinates TO wgs84...<br>
<br>
Ilumas,<br>
<br>
The parameters are always expressed in terms of what it takes to<br>
transform to WGS84. If PROJ is transforming from WGS84 it will<br>
internally reverse the sense of the transformation.<br>
<br>
Keep in mind there is also an issue with the handedness of the<br>
parameters.<br>
Some folks, mostly european, express the parameters with a different<br>
handedness. The scripts that generate the "epsg" init file already know<br>
about this case and convert to the usual PROJ.4/North American<br>
handedness but if you are researching parameters yourself from various<br>
sources you may need to be aware of it.<br>
<br>
Best regards,<br>
--<br>
---------------------------------------+--------------------------------<br>
---------------------------------------+------<br>
I set the clouds in motion - turn up | Frank Warmerdam,<br>
<a href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a><br>
light and sound - activate the windows | <a href="http://pobox.com/%7Ewarmerdam" target="_blank">http://pobox.com/~warmerdam</a><br>
and watch the world go round - Rush | Geospatial Programmer for Rent<br>
<br>
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