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<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial'>Joaquim</span></font><font size=2 color=black
face=Arial><span lang=EN-US style='font-size:10.0pt;font-family:Arial;
color:windowtext'>,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-US
style='font-size:10.0pt;font-family:Arial;color:windowtext'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>I think Thomas’s
point wasn’t that your H/h convention was wrong, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>just that there are
two conflicting conventions used in the literature. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>(I have noted that
the “Guide to coordinate systems in <st1:country-region w:st="on"><st1:place
w:st="on">Great Britain</st1:place></st1:country-region>”,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'> <a
href="http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf">http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'> uses <i><span
style='font-style:italic'>H</span></i> for ellipsoid height and <i><span
style='font-style:italic'>h</span></i> for orthometric height.) <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span lang=EN-US
style='font-size:10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>You also wrote:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> It happens that I
just tested with our Portuguese geoid with following command<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> cs2cs +proj=latlong
+ellps=WGS84 +towgs84=0,0,0 +geoidgrids=GeodPT08.gtx <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> +to +proj=latlong +ellps=WGS84
+towgs84=0,0,0<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> -8 37 0<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> 8dW 37dN 51.910<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> which is fine and
means that the left side altitude was interpreted as ellipsoidal height <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'>> and the output is the
geoid undulation at that point.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt;color:windowtext'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>Well, that’s
one way to interpret the result (and a correct one). That is, the geoid <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>undulation is
+51.910 m, so the geoid surface is 51.910 m above the ellipsoid <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>surface here.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>However, I believe
the intended interpretation is different: The presence of <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>+geoidgrids before
+to means that the input height is an orthometric height, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>while the absence
of +geoidgrids after +to means that the output height is<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>height above
ellipsoid. This interpretation is more general, since the geoid<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>undulation is, in
general, not output explicitly by cs2cs, although it can be<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>calculated as ellipsoid
height minus orthometric height. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>So as I understand
it, your suggested +H/+h parameters are unnecessary,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>since the presence
of +geoidgrids means orthometric height, and its absence <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>means ellipsoid
height. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'>Regards,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:windowtext'>Mikael Rittri<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:windowtext'>Carmenta<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:windowtext'>Sweden<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial;color:windowtext'><a
href="http://www.carmenta.com/"><span lang=SV>http://www.carmenta.com</span></a></span></font><font
color=black face=Arial><span style='font-family:Arial;color:windowtext'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:windowtext'><o:p> </o:p></span></font></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
color=black face="Times New Roman"><span lang=EN-US style='font-size:12.0pt;
color:windowtext'>
<hr size=2 width="100%" align=center tabindex=-1>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span lang=EN-US
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span lang=EN-US style='font-size:10.0pt;
font-family:Tahoma;color:windowtext'> proj-bounces@lists.maptools.org
[mailto:proj-bounces@lists.maptools.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>J. Luis<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, January 15, 2012
9:12 PM<br>
<b><span style='font-weight:bold'>To:</span></b> PROJ.4 and general Projections
Discussions<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Proj] How grids work
in PROJ4</span></font><font color=black><span lang=EN-US style='color:windowtext'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>On 15-01-2012 13:58, Thomas Knudsen wrote: <o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>2012/1/14 Michal Seidl <<a
href="mailto:michal.seidl@gmail.com" moz-do-not-send=true>michal.seidl@gmail.com</a>><o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'>[-- TEXT DELETED --]<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>
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<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-US style='font-size:12.0pt'>So following Joaquim's suggestion of +H and
+h options is quite risky. </span>Out of context you can never be sure what is
meant by H and h.<o:p></o:p></font></p>
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<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>/Thomas<o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><br>
Ai, this is embarrassing for me. Off course I mistakenly swapped the H/h as it
never crossed my mind going against the notation followed by the "Physical
Geodesy" bibles.<br>
<br>
Joaquim<o:p></o:p></span></font></p>
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