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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Hello,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>The Malayan Monster is back! <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>I know that in Proj version 4.8, the implementation
of Hotine Oblique Mercator was replaced<br>
by the version from libproj4. And I know one of the compatibility issues: the
+rot_conv flag<br>
is gone and replaced by the more general +gamma parameter. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>But the behaviour of the “no_rot” flag
also seems to have changed. (We happened to use it<br>
internally.) <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Here is an example in Proj 4.7:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>proj +proj=omerc
+a=6377298.556 +f=0.00332444929666288 +lonc=115 +lat_0=4
+alpha=53.3158204722222 +no_rot +x_0=0 +y_0=0 +k_0=0.99984 +no_defs -v<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#Oblique Mercator<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
Cyl, Sph&Ell<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
no_rot rot_conv no_uoff and<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
alpha= lonc= or<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
lon_1= lat_1= lon_2= lat_2=<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +proj=omerc +a=6377298.556
+f=0.00332444929666288 +lonc=115 +lat_0=4<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +alpha=53.3158204722222
+no_rot +x_0=0 +y_0=0 +k_0=0.99984 +no_defs<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>115d48'19.8196"E 5d23'14.1129"N<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>163238.16
-69702.79<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Using the same definition in Proj 4.8 gives<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>proj +proj=omerc
+a=6377298.556 +f=0.00332444929666288 +lonc=115 +lat_0=4
+alpha=53.3158204722222 +no_rot +x_0=0 +y_0=0 +k_0=0.99984 +no_defs -v<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#Oblique Mercator<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
Cyl, Sph&Ell no_rot<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
alpha= [gamma=] [no_off] lonc= or<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
lon_1= lat_1= lon_2= lat_2=<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +proj=omerc +a=6377298.556
+f=0.00332444929666288 +lonc=115 +lat_0=4<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +alpha=53.3158204722222
+x_0=0 +y_0=0 +k_0=0.99984 +no_defs<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#--- following specified but
NOT used<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +no_rot<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>115d48'19.8196"E
5d23'14.1129"N<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>901334.26
-69702.79<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>The second coordinate is the same, but the first is
quite different.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>And the verbose output says that +no_rot is not used.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>But that’s a lie: if we remove +no_rot in 4.8,
we get <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>proj +proj=omerc
+a=6377298.556 +f=0.00332444929666288 +lonc=115 +lat_0=4
+alpha=53.3158204722222 +x_0=0 +y_0=0 +k_0=0.99984 +no_defs -v<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#Oblique Mercator<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
Cyl, Sph&Ell no_rot<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
alpha= [gamma=] [no_off] lonc= or<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
lon_1= lat_1= lon_2= lat_2=<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +proj=omerc +a=6377298.556
+f=0.00332444929666288 +lonc=115 +lat_0=4<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +alpha=53.3158204722222
+x_0=0 +y_0=0 +k_0=0.99984 +no_defs<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>115d48'19.8196"E
5d23'14.1129"N<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>89266.61
153416.59<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>So +no_rot does have an effect; the question is just
what it does<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>in 4.8. I figured out that I could nearly reproduce
the 4.7 behaviour<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>by omitting +no_rot and using +gamma=0.0; this gives:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>proj +proj=omerc
+a=6377298.556 +f=0.00332444929666288 +lonc=115 +lat_0=4
+alpha=53.3158204722222 +gamma=0.0 +x_0=0 +y_0=0 +k_0=0.99984 +no_defs -v<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#Oblique Mercator<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
Cyl, Sph&Ell no_rot<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># alpha=
[gamma=] [no_off] lonc= or<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>#
lon_1= lat_1= lon_2= lat_2=<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +proj=omerc +a=6377298.556
+f=0.00332444929666288 +lonc=115 +lat_0=4<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'># +alpha=53.3158204722222
+gamma=0.0 +x_0=0 +y_0=0 +k_0=0.99984 +no_defs<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>115d48'19.8196"E
5d23'14.1129"N<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'>-69702.79
163238.16<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>The result is the same coordinates as in the 4.7
example, but in the opposite order. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Maybe this makes some sense: +no_rot in 4.7 says no
rotation, and since we have a general<br>
rotation parameter +gamma in 4.8, it is natural to specify no rotation by
setting +gamma=0.0.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>And the coordinate order is probably weird in 4.7:
the unrotated coordinates are called u and v,<br>
and I believe Martin Hotine defined the u,v coordinate system to be left-handed,
so it seems<br>
that Gerald Evenden followed that design in the +no_rot of Proj 4.x (where x
<= 7). <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>My conclusion is that +no_rot is not needed in 4.8, but
it does have some effect (not sure what),<br>
despite the denial of the verbose output. <br>
<br>
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>If someone understands more about this, I’d
like to hear about it. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Otherwise, you are warned: don’t use +no_rot in
Proj 4.8.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Best regards,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Mikael Rittri<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Carmenta<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Sweden<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>http://www.carmenta.com<o:p></o:p></span></font></p>
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