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<p class=MsoNormal><font size=3 color=black face=Arial><span lang=EN-US
style='font-size:12.0pt;font-family:Arial'>Hello Zoltan, <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'>You wrote:<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'><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'>> My question is: <br>
> Did I specify the s_srs and t_srs parameters correctly<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'><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'>As far as I can see, yes (for what
it’s worth). <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'><br>
> Can I be certain that the SA.gsb grid was used?<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'><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'>I don’t know if there is some
tracing or debugging mode of ogr2ogr or gdalwarp that says<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'>whether an NTv2 grid was used, since
points outside the grid are silently non-datumshifted<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'>(at least in Proj 4.8.0, I think).<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'><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'>However, for your point, I can
verify that it was used:<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'><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'>With cs2cs, I get<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'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>> cs2cs
+proj=tmerc +lon_0=33 +a=6378249.145 +b=6356514.966398753 +nadgrids=SA.gsb +to
+init=epsg:32736<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>-49717.33
-2872272.46<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>450288.90
7128578.77 0.00<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'>(when I have SA.gsb in the right
directory), which is just a few centimeters from your results. <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'>If I remove the +nadgrids parameter,
or use the alaska.gsb instead, I get the result <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=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>450303.95
7128642.46 0.00<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span lang=EN-US
style='font-size:10.0pt;font-family:"Courier New";color:navy'><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'>It is hard </span></font><font
face=Arial><span lang=EN-US style='font-family:Arial'>to know what’s wrong, but
maybe the SA.gsb grid shift file is not very accurate outside<o:p></o:p></span></font></p>
<p class=MsoNormal><st1:place w:st="on"><st1:country-region w:st="on"><font
size=3 color=black face=Arial><span lang=EN-US style='font-size:12.0pt;
font-family:Arial'>South Africa</span></font></st1:country-region></st1:place><font
face=Arial><span lang=EN-US style='font-family:Arial'>, even though it extends
outside the borders. The corrections outside <st1:place w:st="on"><st1:country-region
w:st="on">South Africa</st1:country-region></st1:place><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'>may have been computed from
extrapolation rather than measurements. <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'><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'>(For example, I have noticed this
for the conus grid shift file for NAD27: it has been extrapolated <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'>to cover <st1:place w:st="on"><st1:country-region
w:st="on">Cuba</st1:country-region></st1:place> but is quite bad there.<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'><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'>So if I use </span></font><font
size=2 face="Courier New"><span lang=EN-US style='font-size:10.0pt;font-family:
"Courier New"'>+datum=NAD27</span></font><font face=Arial><span lang=EN-US
style='font-family:Arial'>, I get the default datum shift </span></font><font
size=2 face="Courier New"><span lang=EN-US style='font-size:10.0pt;font-family:
"Courier New"'>+nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat</span></font><font
face=Arial><span lang=EN-US style='font-family:Arial'>, and <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'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>> cs2cs
+proj=longlat +datum=NAD27 +to +proj=longlat +datum=WGS84<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>-75 20<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>74d59'57.145"W
20d0'1.783"N 0.000<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'><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'>But if I use a datum shift that is
more accurate on <st1:place w:st="on"><st1:country-region w:st="on">Cuba</st1:country-region></st1:place>
(“NAD27 to WGS 84 (88)”, EPSG:15978), I get <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'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>> cs2cs
+proj=longlat +ellps=clrk66 +towgs84=2.478,149.752,197.726,0.526,0.498,-0.501,0.685
+to +proj=longlat +datum=WGS84<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>-75 20<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>74d59'58.961"W
20d0'2.043"N -21.720<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'><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'>Horizontally, these differ by 53.4
meters.)<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'><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'>Anyway, back to <st1:place w:st="on">Africa</st1:place>.
If we don’t trust the SA.gsb, we can try with the datum shift “<st1:place
w:st="on">Cape</st1:place> to WGS 84 (2)”, EPSG:1129,<br>
from the Directorate of Surveys and Land Information, <st1:place w:st="on"><st1:City
w:st="on">Cape Town</st1:City></st1:place>. “Residuals should not exceed 15
metres”, says EPSG,<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'>but I think they do.<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'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>> cs2cs
+proj=tmerc +lon_0=33 +a=6378249.145 +b=6356514.966398753
+towgs84=-134.73,-110.92,-292.66 +to +init=epsg:32736<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>-49717.33
-2872272.46<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>450283.06
7128577.97 17.72<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'><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'>Or we can try with the datum shift “<st1:place
w:st="on">Cape</st1:place> to WGS 84 (1)”, EPGS:1128, from U.S. Defense Mapping
Agency TR8350.2,<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'>September 1987, with accuracy 9
metres (confidence 67 percent, I think).<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'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>> cs2cs
+proj=tmerc +lon_0=33 +a=6378249.145 +b=6356514.966398753
+towgs84=-136,-108,-292 +to +init=epsg:32736<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>-49717.33
-2872272.46<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=black 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 color=black face="Courier New"><span
lang=EN-US style='font-size:10.0pt;font-family:"Courier New"'>450286.20
7128578.80 17.88<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'><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'>Unfortunately, it seems that neither
of these would make you very much happier. <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'><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'>As a last resort, if you have more
examples of source and target points that are representative for your area of
interest,<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'>one could use the SEVENPAR program
from Killetsoft to compute a local 3-parameter or 7-parameter transform. <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'><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'>Best 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'><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'>Mikael Rittri<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'>Carmenta<o:p></o:p></span></font></p>
<p class=MsoNormal><st1:country-region w:st="on"><st1:place w:st="on"><font
size=3 color=black face=Arial><span lang=EN-US style='font-size:12.0pt;
font-family:Arial'>Sweden</span></font></st1:place></st1:country-region><font
face=Arial><span lang=EN-US style='font-family:Arial'><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'>http://www.carmenta.com<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 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>
</span></font></div>
<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>Zoltan Szecsei<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, August 28, 2012
10:46 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] Gauss
conformal Lo33 on Clarke 1880 <st1:place w:st="on"><st1:PlaceType w:st="on">Cape</st1:PlaceType>
<st1:PlaceName w:st="on">Datum</st1:PlaceName></st1:place> to WGS84 UTM36S -
NTv2 file needed.</span></font><font color=black><span lang=EN-US
style='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'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span lang=EN-US style='font-size:12.0pt'>Hi All,<br>
This issue goes on, slower than a snail.<o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span lang=EN-US style='font-size:12.0pt'>[ -- Text
deleted. See http://lists.maptools.org/pipermail/proj/2012-August/006407.html --
] <o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span lang=EN-US style='font-size:12.0pt'><o:p> </o:p></span></font></p>
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