<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:st1="urn:schemas-microsoft-com:office:smarttags" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<meta name=Generator content="Microsoft Word 11 (filtered medium)">
<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><o:SmartTagType
namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PersonName"/>
<!--[if !mso]>
<style>
st1\:*{behavior:url(#default#ieooui) }
</style>
<![endif]-->
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman";}
h1
{margin-top:6.0pt;
margin-right:0in;
margin-bottom:6.0pt;
margin-left:.5in;
text-indent:-.25in;
page-break-after:avoid;
mso-list:l0 level1 lfo2;
font-size:12.0pt;
font-family:Arial;}
h2
{margin-top:6.0pt;
margin-right:0in;
margin-bottom:6.0pt;
margin-left:.75in;
text-indent:-.25in;
page-break-after:avoid;
mso-list:l1 level1 lfo4;
font-size:14.0pt;
font-family:Arial;
font-style:italic;}
p.MsoBodyText2, li.MsoBodyText2, div.MsoBodyText2
{margin-top:0in;
margin-right:0in;
margin-bottom:6.0pt;
margin-left:0in;
line-height:200%;
font-size:12.0pt;
font-family:"Times New Roman";}
a:link, span.MsoHyperlink
{color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{color:blue;
text-decoration:underline;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:Arial;
color:navy;}
@page Section1
{size:8.5in 11.0in;
margin:1.0in 1.25in 1.0in 1.25in;}
div.Section1
{page:Section1;}
/* List Definitions */
@list l0
{mso-list-id:1302539220;
mso-list-type:hybrid;
mso-list-template-ids:1400028960 1556136038 67698713 67698715 67698703 67698713 67698715 67698703 67698713 67698715;}
@list l0:level1
{mso-level-style-link:"Heading 1";
mso-level-tab-stop:.5in;
mso-level-number-position:left;
text-indent:-.25in;}
@list l1
{mso-list-id:2076705572;
mso-list-type:hybrid;
mso-list-template-ids:2072013344 127926764 67698713 67698715 67698703 67698713 67698715 67698703 67698713 67698715;}
@list l1:level1
{mso-level-number-format:alpha-lower;
mso-level-style-link:"Heading 2";
mso-level-tab-stop:.75in;
mso-level-number-position:left;
margin-left:.75in;
text-indent:-.25in;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
-->
</style>
</head>
<body lang=EN-US link=blue vlink=blue>
<div class=Section1>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Not true. A round trip will always close.
You’ll have learned nothing about the correct rotation sense. You can
test this yourself. Do one round trip with the rotations unchanged and do
another round trip with the rotations negated. They’ll both close on the
original point. Correctness is determined by the intermediate coordinates
(right or wrong), not by the round-trip closure. –Noel Zinn<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
proj-bounces@lists.maptools.org [mailto:proj-bounces@lists.maptools.org] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Ilumas<br>
<b><span style='font-weight:bold'>Sent:</span></b> Saturday, April 24, 2010
3:02 AM<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">PROJ.4
and general Projections Discussions</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Proj] cs2cs's
+towgs84 usage</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Well, I agree that for assessing the accuracy of the re-projection
results one needs a reference, but that should not be necessary for
understanding the behavior of the cs2cs or the towgs84 string.
Therefore I still argue that the test I suggested below is a valid way to test
whether the parameter values need to be negated or not. Anyone?<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>ilumas<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On Fri, Apr 23, 2010 at 3:39 PM, Jean-Claude REPETTO <<a
href="mailto:jrepetto@free.fr">jrepetto@free.fr</a>> wrote:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Le 23/04/2010 14:24, Ilumas a écrit :<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>><br>
> Anyway, I believe that the behaviour of a certain towgs84 string is easy<o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>> to test with cs2cs itself: just do the transformation to one
direction<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>> (e.g. from WGS84)
and convert the resulting coordinates back to the<br>
> original datum using exactly the same parameter string. If the resulting<br>
> coordinates equal to the original ones, no negation is needed. Right?<br>
><br>
> ilumas<o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Hi,nding the behavious of the cs2cs<br>
<br>
I think you are wrong. To check the parameters, you need to know the<br>
coordinates of at least one point in both datums, and compare them with<br>
the results of cs2cs.<br>
<font color="#888888"><span style='color:#888888'><br>
Jean-Claude</span></font><o:p></o:p></span></font></p>
<div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>_______________________________________________<br>
Proj mailing list<br>
<a href="mailto:Proj@lists.maptools.org">Proj@lists.maptools.org</a><br>
<a href="http://lists.maptools.org/mailman/listinfo/proj" target="_blank">http://lists.maptools.org/mailman/listinfo/proj</a><o:p></o:p></span></font></p>
</div>
</div>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
</div>
</body>
</html>